m0xpd's 'Shack Nasties'

In a Spin

2012-02-12T10:59:00.028Z

Aside from admiring, owning and using them, your humble servant is now active within the global economy of Leslie Speakers, having jointly developed an accessory which is commercially available. More of that sordid, mercenary semi-professionalism later. First, true to my Ham credentials, I'd like to share some details of my new Leslie interface, just for the love of it.

Readers have learned how I got my first Leslie, an 825, from Bob, just down the M56 in Chester. A couple of weeks before Christmas, I got another Leslie from another Robert, a little further west in Holywell. I'm pretty sure that the relative remoteness of Chester and (particularly) Flintshire kept the prices down to my beer-budget levels.

The new (old) Leslie is a 125 - similar to the 825 in that is has only a single speaker (but that's about to change - watch this space). The 125 is, however, critically different in at least three important respects. Firstly, it has a veneered wooden enclosure (rather than the ugly "Tolex" vinyl covering of the ProLine 825) - it LOOKS like a Leslie. Secondly, it has a valve(/tube) amplifier, with all the romance that entails. Thirdly, it uses a different interface to the outside world.

The 825 uses Leslie's "9 pin" interface, as described in this previous post. It achieves speed control by a simple, low voltage switching scheme, ready for plug 'n play connection to my homebrew half-moon switch.

The 125 uses an older interface standard, called "6W". The 6 indicates the fact that there are only 6 conductors in the cable to the speaker (and 6 pins on the special, expensive Amphenol connectors). The "W" actually stands for Wurlitzer, in order to differentiate from another contemporary six-pole Leslie interface, "6H", in which the "H" meant Hammond. The 6H interface was used for - you guessed it - Hammonds, as exemplified by the Leslie 122. The 6W interface, developed from a Wurlitzer wiring standard, is also called the "Universal" interface and is used for other applications, as in the Leslie 147. These two interface standards are dangerously INCOMPATIBLE, yet they share the same physical layer in the special "6 pin" connector cable, which is used in both standards.

Here, for my own records as well as your edification, are the pin assignments in the 6W standard...

Pin	Colour	Function
1	Black	Signal Ground
2	Yellow	Motor Relay
3	Gray	AC Power In
4	Blue	AC Power In
5	Brown	Motor Relay
6	Red	Signal Input

The colours refer to the cores in a real Leslie cable.

Note the apparently inoccuous pins 2 & 5, connected to the Motor Relay. In order to switch between the two available speeds ("chorale or tremolo"), one has to apply 240V AC between pins 2 and 5 (in the UK at least). Speed control certainly isn't a "simple, low voltage switching scheme" and it implies switching mains electricity. No voltage gives tremolo (the fast rotor speed) and 240V gives chorale (the slow speed).

Call me a wuss if you like, but I have a pretty well-developed fear of high voltage electricity. It all started when my childhood friend, Paul Sibley, tried to stop the smell caused by a budgerigar feather burning on the element of a small electric fan heater. Paul used a pair of scissors to remove the feather with predictable results. He flew across the kitchen at altitude of about six inches and slammed into the opposite wall. Mr Sibley was a successful builder who had built his family an impressively proportioned home, so Paul's trans-kitchen flight was a long one. He survived and I learned what has proven to be a useful life lesson.

With all the baggage of burning budgie feathers, I wasn't about to go switching mains voltages on my virtual organ console. I don't think the guitar pickup selector switch in my homebrew half-moon switch would have handled 240v AC - much less, into slightly inductive loads. So - a safer switching scheme was indicated...

Of course, I could have simply used a relay to switch the voltage to the motor relay (big fleas have little fleas upon their backs...) and used the Telecaster switch to energize the local relay coil at low voltage. That, however, wasn't entirely true to the spirit of the ideas brewing in the back of my mind for more flexible speed switching options, including 9-pin, 6-pin and maybe even 11-pin interface compatability, so I added a little electronics.

Here's the low-voltage aspects of my speed control circuit - it is based on a somewhat over-specified relay from Maplin (which required me to learn again for the umpteenth time how to create a new part for Eagle). The design includes a stabilized 12V supply (not strictly needed for the switching operation, but important for the rest of my design, as you'll see in a moment), which is at the top of the schematic below.

I've edited out all the high voltage parts of the circuit. I don't want to be held responsible for people who haven't learned the consequences of burning budgie feathers.

Here's the switching circuit in the flesh...

Still glowing with the success of my pre-amp for the 825, with its HF shelving filter, I made another identical circuit for use with the 6W interface...

All these printed circuit boards are all very well, but they only become a practically useful system when placed in an enclosure with the appropriate connectors. In sourcing a suitable box I learned that some of Maplin's enclosure range is to be discontinued - I hope this isn't yet another stage in the long, drawn-out demise of this once-useful source of components. (For overseas readers, Maplin is a high street retail chain filling the spot once occupied by Tandy - the UK version of Radio Shack. Until five or so years back, Maplin rivalled the big "trade" players in component supply with on-line and high street options. The demise of hobby electronics (indeed, of any practical pursuit) and the nonsense of trying to provide it on the high street has driven Maplin's metamorphosis into yet another consumer electronics / tech store. I doubt they will survive much longer.)

Anyway, here are some shots of my finished 6W interface, allowing the 125 to be connected to my virtual organ (i.e. a computer soundcard) or anything else which can produce close-to line level audio into high impedance.

The big red switch turns on the whole shooting match (including the Leslie) and the two controls on the front are for volume and HF boost.There are internal jumpers selecting 0, 10 or 20 dB overall gain. On the rear are mains inlet via an IEC socket, the 6-pin chassis socket (I splashed out and purchased a 32.5mm hole punch to add to the collection), audio input via 1/4 inch jack and speed control via a 3-pin DIN (as used on my other "pre-amp"). It works perfectly and makes hooking up the 125 (or any other Leslie using the 6W interface) a walk in the park.

Here is the finished 6W interface unit, sitting atop the 825 (the 125 is on the other side of the room).

Now to return to the commercial world...

I was chatting with Hammond and Leslie expert George Benton, after reading of his adventures using a Hammond Super B console as controller for a virtual organ. George had seen the games I was playing with PICs in an organ context and asked if I'd like to join in developing a speed controller for Leslie speakers. I accepted, thinking I'd learn from the experience and from friendship with George - both have turned out to be the case.

First, a little explanation.

Early Leslie speakers (the 21H, 22, 22H, 22R, 31H, 44W, 45, 46, 47and 51) were single speed (or, at least, single speed plus "stationary"). Later models evolved to the more familiar two-speed operation mentioned above. It will come as no surprise to hear that the old, single speed models are coveted and valued for their special, desirable properties, real and imagined. Prices soar accordingly. Despite this, owners of single speed units also like the two-speed feature, so opportunity exists for electronic speed controllers able to convert a single-speed unit to two-speed operation. A number of such controllers are available.

George had the bare bones of such a system but needed to develop software - enter yours truly.

Our Leslie speed controller is a fairly standard motor control application, using Pulse Width Modulation techniques. The motor is placed in an H-bridge, formed of IGBTs, under the supervision of a PIC microcontroller...

Although Motor Control is a standard PIC application, we chose (for legacy reasons) to use a very simple 8-pin PIC with no hardware Capture/Compare/PWM module. This made the entire project a matter of trying to squeeze a quart into a pint pot. Not in terms of memory capacity or computational load - rather in handling the time constraints imposed by the interrupt-based software PWM modulator I developed.

The single-speed motors are built to run at "tremolo" speed when driven by 110V, 60Hz, so the controller generates this output signal when "tremolo" is requested. The motors can also be persuaded to run at slower speed, appropriate to "chorale", by lowering the frequency. However, this drop in frequency is accompanied by a drop in the inductive impedance offered by the motor, such that the motor passes more current and runs hot. This can be countered by dropping the voltage magnitude and frequency in "chorale". However, the motor speed is actually a complicated, non-linear function of both voltage magnitude and frequency, all of the consequences of which are anticipated and handled in the control algorithm.

Transitions between each speed (the controller also has a "stop" mode, giving stop, chorale and tremolo as the three available operating speeds) are handled with various boost or brake options, some of which can be selected by the installer.

What with the adaptive interrupt service routine and several other "smarts", there's quite a lot of innmovation and intellectual property in the controller. George and I are real proud of it!

Here is my development platform for the code - I implemented the IGBT H-Bridge on the white PCB for development purposes, but never connected it to a motor...

Here's the final product, which replaces the relay in a single speed Leslie...

It was rather time consuming developing real-time motor control software on one side of the Atlantic and testing it on harware on the other - but we got there! Learning the obvious lesson from that geographical separation between development system and target, I now have assembled all the bits required to add a horn, under the control of our speed controller, to my 125. I also have the single speed motor for the LF unit, so it will go "all electronic".

This will make development of the next versions of the controller a whole lot easier - plus I get to have a great organ speaker!

Over the past few days there has been some disquiet as the Bank of England engages in the Carollesque delusion called "quantitative easing". I can't see any real economic benefit in that. Instead, why don't you make a real difference by heading off to the Benton Electronics on-line store and getting yourself an MTCLogic 2-speed Leslie controller.

Every home should have one. At least, every home with a single speed Leslie.

...-.- de m0xpd

Top Totty

2012-02-03T10:55:00.003Z

Isn’t it heart-warming to know that, despite the imminent threat of economic Armageddon, with all its collateral, our politicians still have time and energy to devote to matters of grave import.

I understand from her website that Kate Green MP twitted (sic) to the effect that Slaters’ branding for their blonde beer ‘demeans women’. Although her actions can hardly further demean the laughing stock that is the political class, Ms Green undoubtedly has demeaned the cause of equality.

I have the good fortune to live in Ms Green’s constituency . Evidently, I do not have the good fortune to have my views “represented” (in any sense) by the local MP.

Cheers Kate!
...-.- de m0xpd

More Matters Enigmatic

2012-01-22T15:32:00.014Z

It has been so long since my last post that part of me feels like making an apology - but the bigger, better part reminds me that this is for my pleasure and recognizes the potential danger of becoming ruled by a compulsion to blog, so I'll continue as if nothing has happened...

Amongst the many nice gifts I received at Christmas was a(nother) book about Bletchley Park, to add to those already devoured (some of which are reported elsewhere in these ramblings).

This time, it is Sinclair McKay's book "The Secret Life of Bletchley Park"...

This was a pleasant-enough read, different from all the other technically focussed books in that its subject is very much the people at BP and the context in which they served. The book looks at social, domestic and human aspects, without spending much time on the cryptanalytical methods and technologies at the core of the work. Also - unusually - the book doesn't become too distracted by the "celebrities", affording equal weight to some of the humbler folk on which the activities depended.

McKay describes the experiences of those who worked at BP, drawing heavily on other published materials and (apparently) a few interviews with veterans. We are given a glimpse of working conditions, billeting arrangements, recreational and cultural activities, romances between staff members and dealing with the imperatives of secrecy - both during and after the war. The book concludes with some descriptions of how BP veterans dealt with the changing conditions after the hostilities and attempts a brief sketch of the broader legacy of the work at Bletchley Park.

It is a rewarding read, but might have been better edited, not least to avoid an irritating sense of repetition. The book tries to assess the broader legacy of BP's work and occasionally is marred by repetition. [ed: scratch that - you've said it already]

Whilst we're adjacent to the subject of "Enigma", may I commend to the attention of British readers the weekly "Enigma Code" puzzle in our beloved "Radio Times"...

I'm no puzzle junkie, tending to sneer at Sudoku addicts, but this particular game interests and entertains me.

It takes the form of a "crossword without clues", in which all the squares are numbered with integers corresponding to the letters of the alphabet. Your task, should you decide to accept it, is to associate numbers and letters!

Give it a try - I saw a fellow passenger on a flight doing the same type of quiz from a different newspaper recently. I don't know which paper it came from, but I can confirm there are more of these puzzles out there if you become hooked.

Fortunately, I'm not the addictive type!

...-.- de m0xpd

Pedalling like Fury

2011-10-31T15:58:00.022Z

I was fortunate to pick up an old, worn, dirty set of Hamond C3 padals on eBay for a fiver back in August. Here they are at the start of the "resurrection" process...

After a lot of elbow grease (most of it from my wife, who generously contributed her domestic skills and cleaning products) the pedals looked much cleaner. They also worked rather better, as I had replaced any badly worn felts, some of which support each pedal laterally between vertical guide pins. Finally, I had stripped off the galvanized brackets which support the operating "tabs" which do the actual switching in the real Hammond Organ (which is why this is a "resurrection" rather than a "restoration").

From this angle, perhaps you can see why I believe the previous owner(s) preferred playing in the key of F!

I wanted to use these pedals in my virtual organ project (Blogs passim), which meant that they had to be able to operate as electrical switches rather than hinged pieces of wood. There are a few technology options here for the organ builder:

you could arrange for each pedal to touch and operate a miniature switch as in this example
you could make electrical contact pairs (or one contact per pedal and one or more busses) for each pedal and make a physical switch as in this example.
you could use an optical method, with a "shutter" tab on each pedal and a opto-detector making the translation from optical intensity to an electrical switch function
you could use a magnetic method, placing a magnet on each pedal and using a Hall Effect sensor adjacent to each pedal to convert the magnetic field to an electrical switch function
you could usea magnetic method, placing a magnet on each pedal and using a reed switch adjacent to each pedal to convert the magnetic field to an electrical switch function as in this example

There are examples of each of these methods on the internet.

I wanted to use the Hall Effect method, but I couldn't find the sensors cheaply enough (you should know me by now), so I stuck with the trusty, cheap reed switch technology...

I put 3mm Neodymium rod magnets into a hole drilled in the end of each pedal...

You can see the vertical guide rods and the felts, mentioned previously.

I also made up a series of perspex panels (chosen for its transparency, which made alignment with the magnets during "marking up" and subsequent assembly easy), each holding five or seven reed switches. I made brackets to support these panels, mounting under the nut and lock washer that secured the guide pins - the whole process involved no "butchery" of the pedals, except the magnet holes. One of the (five switch) panels is seen, in-situ, below...

I have described previously how my single-octave pedals were wired up and converted to MIDI. The same process was used again - with one significant exception...

The pedals are scanned as a matrix of (4) columns and (7) rows, the last having only one pedal (25 notes takes 6 rows of 4 and a single "extra"). In the previous encoder system, it was known that you could not play more than one pedal in a single column together whilst playing another pedal from another column without the possibility of additional notes sounding. This wasn't seen as a problem as playing two pedals in one "column" constitutes an interval of a minor third or less, which isn't done in the bass register (it is psycho-acoustically and musically meaningless).

However, the geometry of the new pedalboard made it easier for me to arrange that the reed switches should be normally on, switching to open circuit when a pedal is depressed. This meant that, from the point of view of my encoder scheme, all the notes in every column were being "played" most of the time - the system didn't work!

The solution is well-known and simple - you just add diodes in series with each reed switch et voila. Of course, I had to invert the logic of my encoder program (to send a "Note On" command when a reed went open circuit and vice-versa) but that was the work of moments.

Here's the expanded version of my pedal encoder system, capable of running 25 keys (plus seven spares for "toe pistons" or whatever) and the expression pedal...

The trouble with a two octave pedal board is that you need a real organ bench to sit "over" the pedals. Fortunately, eBay came to the rescue again, with a genuine Hammond A-100 bench...

I'm very surprised how easily this went together - I was frightened that the reed switches would be very difficult to set up, but they were easy. Careful location of the magnets (using a jig to drill the pedal ends) and equally careful marking up of the perspex carriers made it work first time.

All I need to do now is get out of the habit of stopping at that formerly top - now middle C!

...-.- de m0xpd

Shelving Audio Filter

2011-10-26T04:45:00.035+01:00

I was fortunate to pick up a Leslie 825 speaker for my virtual organ project (Blogs passim) for a song on eBay...

Part of the explanation for the attractive price was that - as the seller put it - this is "a Leslie 825 speaker with a difference".

I'll let the seller go on with his description:

"the difference is that the (previous) owner had a number of keyboards and he modified the cabinet by inserting two other speakers front and back - he drilled holes in the cabinet and placed a grill over the front - the grill is available but is not in the picture so that you can see what lurks beneath".

Well, now YOU can see the ugly array of holes in the picture above. I have fixed the grille on to make thinks look a little less unsightly and, like the seller, I haven't yet bothered to test the additional speakers. But the Leslie itself works well enough (with one trivial exception, to be described below).

For those of you who don't know, a Leslie speaker includes rotating mechanical elements (horns and/or baffles) to introduce a cyclical variation to the radiation from the loudspeaker which, in interaction with the acoustics of the performance / listening space, makes some interesting spatial audio effects involving amplitude and frequency modulation and comb filtering. It was developed by Don Leslie...

in an attempt to emulate the chorus effect produced when ranks of (inevitably somewhat de-tuned) organ pipes speak together, giving electronic organs a "pipe voice". The mechanical components are contrived to rotate at one of three different speeds (slow/stop/fast or, to respect the orthology, chorale/stop/tremolo) under the control of the iconic "half-moon" switch. Paul, g1dva, tells me he has seen rotating speakers with continuously variable speed control - but we'll dismiss these as pathological. Certainly, the classic Leslie only operates at a few discrete speeds, latterly the three described above.

Older Leslies used a horrible electrical interface, in which mains power, control signals and the audio were all applied through a long, multi-way cable terminated with special (i.e. expensive) Amphenol connectors. In the case of the 825, it is a 9-pin system, with the following connections...

Pin	Colour	Function
1	Black	Ground
2	Red	Input
3	Yellow	No Connection
4	Orange	Stationary Input / Aux Control (not used in 825)
5	Green	dc Output (+28V)
6	White	Slow Motor Control
7	Violet	Fast Motor Control
8	Gray	240V In
9	Blue	240V In

(The colours are those of the cores of the "official" Leslie Cables).

The seller of my 825 kindly gave me a 9-pin cable to connect up the device - thanks Bob!

Well, I had the cable but no socket for the organ end, so I lashed things together with a very unsafe Heath Robinson connection, involving individual pieces of "Choc Bloc" connector...

on each of the pins of the plug - DO NOT TRY THIS AT HOME, CHILDREN!

All this gave me opportunity to confirm that the speaker was working, to bask in the glorious spatial effects of a real Leslie (emulations only work up to a point) and - after the honeymoon was over - to become disappointed with the sound!

The 825 has no horn (and associated HF unit) - only a large "full-range" speaker firing through a rotating drum. In consequence the top end is hardly what might be described as "sparkling". In fact it is so poor that I began to think there was something wrong with the "key click" function in the fantastic VB3 software and I actually contacted the programmer before realising that the problem lay right there in my new 825 - sorry Guido!

All this led to some creativity - I acquired a 9-pin socket to replace the temporary lash up (thanks George) and I decided to build a filter to boost the HF response and try to rescue some of the sound. The (sound card) output from my virtual Hammond wasn't enough to drive the speaker to satisfactory levels, so a Pre-Amp stage with some gain was indicated too.

Here's my HF shelf filter, seen as an extract from the LTSpice simulation of the entire circuit...

The series combination of R5 and R6 was actually realised with a potentiometer, configured to give me a variable HF lift. Here's the magnitude response simulated in LTSpice for an arbitrary setting...

The lift above 1kHz is the "shelf", made into more of a "bump" by the low-pass corner (deliberately) introduced by R1||C4.

I turned the idea into reality in a nice sloping front RS box, picked up at a rally somewhere, intentionally copying the format of the Leslie "Combo" Preamp. Here are the innards...

and here's a view of the back panel...

In addition to the variable high frequency shelf, there is an internal jumper to select 0, 10 or 20 dB overall gain and an external volume control. I haven't had chance to fit knobs to the controls yet!

There is (as is usual) a fly in the soup - the "d.c. output" from my new Leslie (pin 5) isn't working. I looked at the schematic and there is little to go wrong (I suspect a dead diode, D14, or an open connection), as the d.c. comes straight from the power supply to the amplifier driver stage, which most emphatically IS working! Still, at the moment, my new PreAmp is powered from a PP3 battery.

Result - FANTASTIC. The 825 is totally transformed and a pleasure to use.

I have some rather more exciting Leslie-related stories to tell - but they can wait for another day.

For now, I'm all in a spin!

...-.- de m0xpd

Update: Fly Rescued from Soup!

This evening I made up a shorter cable for the 825 - having 30 feet of cable coiled up is a recipe for trouble, not to mention hum. I so doing, I discovered that the 28Vdc issue isn't a speaker fault at all - just an intermittent connection in the long cable. The shorter one is fine (with new connectors) so now the PreAmp is powered from the Leslie as planned.

Most Secret War

2011-10-18T21:09:00.005+01:00

Just finished reading R.V Jones' autobiographical book "Most Secret War, British Scientific Intelligence 1939 - 1945"...

being an account of his work as leader of the Air Ministry's Scientific Intelligence Section in WW2. In short, the book is a masterpiece and a must-read for anybody remotely interested in some of the technological and scientific tussles between the allies and the Third Reich.

I purchased the book during my last visit to Bletchley Park and there is obligatory mention of the activities of the Code-Breakers in providing the most reliable of data streams for the Scientific Intelligence community in the UK - an "anchor of truth", as the author describes it (p 530).

There is much else to entertain those with radio-related interests - including the detection, understanding, prediction and ultimate jamming of the radio navigation beams by which the Luftwaffe we able to achieve accuracy in their bombing activities and the similar location, interpretation and jamming of the radar systems which allowed German night-fighters to engage Bomber Command missions over Germany. However, beyond these triumphs, it was the author's involvement in the development and deployment of the countermeasure we now call "Chaff" - then inexplicably known as "Window" - which impressed me most.

This is a giant of a book, fully deserving the hyperbolic notices which adorn its paperback cover ("Among the best of all war books", "Every bit as good as a Deighton or Le Carre Yarn").

Yes - this deserves to be read. Unfortunately, in reading it, I found myself admiring Dr Jones' achievements but becoming anything but warm toward him as a person. Perhaps that's a by-product of the determination and single-mindedness that made him so successful in his great work.

What would I give for determination and single-mindedness?

Not a lot!

...-.- de m0xpd

Requiescat in Pace

2011-08-31T09:41:00.006+01:00

Saddened to hear news of the death of Anthony Edgar "Tony" Sale, whose work on the rebuild of Colossus was central to the preservation of Bletchley Park and the establishment of The National Museum of Computing.

Tony was there tending his creation when I visited Colossus last year - he leaves a legacy not only in the physical rebuild of the machine, but also in the enthusiasm he fostered in a team of colleagues who helped with the rebuild and now ensure the preservation of some important pieces of history.

...-.- de m0xpd

A Splendid Jaunt

2011-08-28T14:45:00.033+01:00

Just back from a few days in the beautiful surroundings of Pickering, North Yorkshire, where we stayed in a delightful cottage conveniently positioned mid-way between a trout lake and a railway station - the very 'gate of heaven'!

Whatever Kirstie and Phil might bang on about, this establishment didn't just rest on its location laurels - it was beautifully presented as well. In addition to the little two-bedded cottage in which we stayed,"The Limes", the good folks at High Mill also have a larger property for rent, which sleeps up to 12.
The view from my armchair was fantastic - here's 7F 0-8-0 heavy duty freight locomotive 49395 working a passenger service tender-first back to Grosmont...

We took the same trip ourselves a few days later, travelling back from Grosmont in fine style in the first class observation saloon at the end of a nice rake of wooden LNER coaches (you can see the new Barbour Beaufort I got from the Orvis store on Pickering's Market Place hanging over the back of my armchair)...

The staff at the Orvis store deserve special mention as they honoured the "£20 off" voucher that came with our railway ticket, even though I'd purchased the coat two days before!

Things took a turn for the better when some thoughtful chap came and offered us drinks - here's my "Gin and Tender"...

(the tender being that of the 9F engine 92214 "Cock O' The North", which strained and sighed on the other side of the glass whilst pulling us back to Pickering).

Here's the observation saloon from the outside on reaching the shelter of Pickering Station's new roof...

Aside from many other notable delights (Gannets at Bempton, the Castle atop the hill behind High Mill and a sublime piece of rib-eye steak at The White Swan), the trout lake served up its usual entertainment...

I think it is actually bigger than the one caught in April - certainly your humble servant looks pretty pleased with himself...

If you want a break in a great location, give High Mill a try - seen here photographed from the observation saloon...

I certainly will be going back.

The only fly in the soup was the trouble I had getting any signal out (2W on 40m CW from the FT817 and Whip). Still, the Mill is on a road called the "Undercliffe" - the clue's in the name!

...-.- de m0xpd

Heavy Artillery

2011-08-20T12:20:00.014+01:00

The same sale of surplus gear that bumped up my BNC socket stocks also saw me bid a tenner to win a wideband RF power amplifier, which runs 12 Watts, 200 kHz - 32 MHz, made by RF Power Labs, Inc. of Kirkland, WA. It had Albert, G3ZHE's sticker on it, so I knew it had come from a good home. Albert told be that previously it had been in Jim G3NFB's shack - it is nice to be keeping it in the Warrington family!

Today, I had chance to power it up and see what it does...

I hooked it up between the output of my multi-mode beacon (Blogs passim), which happened to be set to the 30m band, and the G5RV. Here is the "brick" on the bench...

You can just see one of my switched attenuators atop the amplifier, throwing away some of the input (the amplifier needs 1 Volt in for full rated output).

I was immediately spotted on WSPR in the USA by Edmund, WB1FIG, in Plainville, Massachusetts...

having previously only been heard in Europe.

I do get into the US on occasion with the standard 50mW on 30m, as demonstrated last night, when Douglas, W3HH, heard me once again in Florida...

Having fired WSPR signals over the pond with my new "big gun", I had a look to see if my other modes were being heard further afield. Sure enough, I could just make out my FSK-CW and Hell signals on Bill, W4HBK's grabber in Florida (although you do need to know where to look)...

Of course, the QRSS modes into Europe were loud and clear, as seen on Joachim, PA1GSJ's grabber...

In fact, Joachim was also reporting spotting my WSPR signals both during and after the 5 Watt QRO test. Switching from 5W back to 50mW is a x100 change in power (-20dB) and, sure enough, Joachim's reports showed pretty much a -20dB degradation in SNR between two adjacent spots...

So - the bench RF amplifier works a treat.

Apologies to anybody offended by the fact that I couldn't be bothered to change reported power in my WSPR message during the short test - it is a chore re-programming the PIC - mea culpa!

...-.- de m0xpd

Italian Job in Toytown

2011-08-14T12:41:00.013+01:00

The XYL's father is something of a model railway enthusiast - the photo below reveals the ironic understatement...

During our last visit (in which I took the photo), he asked me to make a traffic light controller - no doubt in an attempt to bring order to the anarchic road-rage one otherwise meets at a 1:76 scale crossroads.

Of course, a traffic light controller is a pretty trivial problem in Finite State Machines 101, so I quickly whipped up a system based on a PIC16F676, with on-board LEDs to monitor progress and open collector outputs to switch on and off the "grain-of-wheat" bulbs which the Toytown traffic engineers have used.

Here's the system under prototyping, connected to my PICKit2...

and here's the translation to a PCB...

All pretty dull. So I decided to fool around a little...

Readers will remember the havoc that can be wrought by messing with traffic lights, as demonstrated in the movie classic "The Italian Job".

I decided it would be fun to introduce an occasional state of confusion in the traffic signals on my father-in-law's railroad - so I programmed in a display which would look good on the Golden Mile...

(Interesting how the video - captured by my iPhone in low light conditions - is incapable of resolving the colour of the bright monitor LEDs)

The traffic light chaos only kicks off every 200 complete cycles, so you have to be watching the lights (or driving past at just the wrong moment in a 1:76 scale car) to see it.

Let's see if he notices!

...-.- de m0xpd

Appreciation as Grabber Goes QRT

2011-08-08T17:26:00.003+01:00

A few days ago on the KnightsQRSS Mail List Johan, on5ex, announced that his excellent QRSS grabber is soon going QRT.

Johan and his grabber have been giving wonderful service to me and to many QRSS operators for many years. In fact, it was Bill Meara's talk of this mysterious station up in Belgium picking up signals from The Eternal City which started my interest in QRSS.

Johan became the second station to report seeing my own QRSS signals and has been picking me up ever since (including back in the day when my Hellschreiber was UPSIDE DOWN!!).

So - now its time to say a huge THANK YOU to Johan and to wish him every success in his new games with other radio modes.

73 dr OM Johan,

...-.- de m0xpd

Enigmatic déjà vu

2011-08-08T16:24:00.026+01:00

I was lucky enough to find myself once again in striking distance of Bletchley Park yesterday and enjoyed another interesting visit. Just like last time, the Battle of Britain Memorial Flight treated us to a fly-past - this time by a Spitfire...

Having last time focussed much attention on Colossus, I was determined to spend a little more time looking at the Bombe (which itself has been the subject of a re-build project) ...

I was fortunate to be able to chat with one of the guides, who explained in considerable detail the operation of this impressive machine. I don't know her name or her background, but she certainly understood operation of the Bombe in depth and I am grateful for her expertise.

Talking about expertise, I was pleased to chat once again with David Wright, g3zpa, who gave me some more information about the original (long-wire) antenna systems supplied for use with the Paraset.

In addition to the aircraft flypast, there was an impressive gathering of classic cars with the inevitable superabundance of MGs (I'm allowed to say that as an MGB owner)...

However, other marques were well represented too. The car of the show (for me at least) was a drop-dead-gorgeous Alfa Giulia Veloce - but I was pleased to see some nice 3-wheeler Morgans...

These 3-wheelers are of interest partly because the XYL's grandfather used to own one and partly due to their pivotal role in the plot of Dorothy Leigh Sayers' "Have His Carcase". Morgans more generally have a place in my heart as the XYL and I went on honeymoon in a 4-4. Happy days!

Cars and aeroplanes aside, there was lots more to interest me at BP - not least in my first visit to The National Museum of Computing which, appropriately, is in the same building as Colossus. After seeing the PDP8's of my youth I was pleased to see a healthy display of analog computers (which - for those of you who don't know - solve differential equations by electrical ANALOGY) amongst which was something I'd never seen before: a hybrid analog AND digital computer...

In truth, it was an analog computer with a few digital elements (flip-flops etc) along the bottom "row" in the photo above.

I was also delighted to find an example of the main board from a Tangerine "microTan 65"...

One of my first computers was built around this 6502-based system marketed as a kit by Tangerine. There was a basic interpreter, a disk operating system and all sorts of goodies. Nice to see it again!

However, the high spot of my visit to the National Museum of Computing was certainly the Domesday systems, based on BBC / Acorn hardware and in the news recently because of the "Domesday reloaded" initiative. Here's one of the two working systems at BP...

We were staying with the in-laws, near Pulloxhill, Beds., so we used the amazingly modern multi-media interface to search for Pulloxhill and pulled up a picture of the characteristic water tower...

Here's a link to the photo on the web-based Domesday Reloaded resource.

Partly (I am told) in consequence of the recent financial debacle at the RSGB, the new radio centre isn't yet open to visitors...

... but we did call into the MKARS club house (in an old generator building on the BP "campus") where I had a nice chat with Graham, a G7 licensee (I missed the rest of his call), before driving back to Pulloxhill.

On the drive back we stopped to take an up-to-date shot of the water tower...

Sitting outside drinking a cup of tea half an hour later, the day was crowned by an unexpected flypast of a Consolidated Catalina, the conspicuous lines of which were unmistakable even at altitude...

I assume she was G-PBYA, which is "berthed" at Duxford - she certainly was heading in the right direction!

Perfect end to a(nother) grand day out!

...-.- de m0xpd

Harvesting Parts and Knowledge

2011-08-06T16:09:00.013+01:00

My attendance at weekly meetings of my radio club has been rather patchy of late (pressures of work intruding on the finer things in life), but my last visit coincided with a Sale of Surplus Equipment, at which we managed to capture some of the excitement of the last few minutes of Bargain Hunt (albeit with more desirable items for sale, naturally). In addition to a nice Linear Amplifier (which allows me to make vulgar QRO emissions at 12 Watts, should I ever want to get involved in EME or similar games Hi HI) I was winning bidder on an old piece of kit which bristled with silver plated BNC sockets - 19 in number...

Perhaps you can make out the label - "Junk but spare sockets". A 50 pence bid secured the item.

A side panel carried identifying marks, revealing the object to be from the Hewlett Packard stable...

but some searching on the 'net hasn't provided any more information on pedigree, use, date or other aspects of provenance.

Taking off the sides revealed a set of 11 parallel "channels" (ten of which are connected to BNC sockets on the "front" and the last of which leads to a socket mysteriously located off on one side)...

Casual inspection suggests the unit is some kind of switching/multiplexing device (the clue was in the name on the side of the box!!) with a number of input signals multiplexed onto a number of output channels, using diode switching. The channel select and other control signals apparently were applied through the Centronics-style connectors seen at the right-hand end of the photo above. The whole thing was beautifully built - seemed a pity to pull it to pieces - but here's one channel stripped out of the enclosure...

At this point I had completed the harvest of BNC sockets - now I was about to harvest a different resource.

You can see a line of devices in glass envelopes protruding from the bottom of the board in the photo above. Unsoldering one confirmed my initial identification as a diode and a quick test with the multimeter showed a forward voltage drop which suggested the diode to be of the Germanium persuasion.

I couldn't see any identifying marks, but the glass envelope was clearly marked with colour rings - as on a resistor...

I figured the colours were brown - white (or, possibly, grey) - green (with a rather indistinct black blob at the other end). I had never seen colour coding on a diode before - so off I went to the internet to search for an explanation.

I learned two important nuggets of information, completely new to me...

Firstly, colour codes - exactly those familiar to us from resistors - were indeed used on diodes and semiconductors in general. That made these diodes "195"s - but that didn't make much sense. Until I recognized a second fact which had been staring me in the face for decades; semiconductors were often named using a system in which the device type (i.e. diode) was followed by a numerical name. The device type was signified by the Number of junctions ("N" for number).

According to this scheme a "1N" device is a diode (there being one P-N junction defining a diode), as in the entirely familiar 1N4148. Similarly, a "2N" device is a transistor (there being two P-N junctions in a [BIpolar Junction] Transistor), as in the entirely familiar 2N3904. It is so entirely obvious when you think about it that I'm surprised I'd never realized before!

I am used to learning something about the nature of a valve/tube from its (alpha-numeric) name - as in an ECC83 being a double triode and a PCL86 being a triode-pentode, the E and the P signifying different heater requirements. However, despite a lifetime of using diodes called 1Nxxxx and transistors called 2Nxxxx, it simply never occurred to me to notice the significance of "1N" and "2N".

So - as well as a rich harvest of BNC sockets, I also had harvested some knowledge. Unfortunately, I'm still not yet out of the woods, because I don't yet know how to put all the pieces of the jigsaw together...

Does the "195" on my diodes mean they are 1N95s? Sure enough, there is a Ge diode called the 1N95. However, my internet researches suggest that the "1N" identification of a diode wasn't included in the colour coding scheme, suggesting that the diodes are 1N195s. The 1N195 seems to be a Si device, which isn't consistent with the 0.23V forward Voltage drop I measured.

If anybody can explain this, I'd be interested to hear from you.

...-.- de m0xpd

Gyrator Analysis 2

2011-08-06T15:07:00.029+01:00

Recently I posted an analysis of a circuit called a "Gyrator" - only to realize that it was wrong! I'm interested in the gyrator having used it in a design for an active CW Filter, recently published in SPRAT.

Fortunately, I spotted my mistake before suffering the indignity of having somebody point it out and I updated the original post with a warning that the so-called "analysis" was nonsense. I also promised to correct it - so here we go...

The circuit under consideration is shown in the image below...

We start the analysis by noting that the voltage at the non-inverting input to the op-amp can be related to the input voltage using the potential divider equation (it was at this stage I made one of the dumb mistakes in my previous botched analysis)...

Ideal operation of the op-amp (which here is set up as a voltage follower) will force the voltage difference between the inputs to zero, such that...

We're now ready to solve for the two currents i₁ and i₂ – we start with i₁

Substituting for the voltage at the non-inverting input gives...

(Microsoft's Equation Editor has done a pretty poor job of laying out this equation - but life is rather too short to do anything about it!!)

Next we turn our attention to i₂...

Now we have both currents, we're able to solve for the input impedance of the circuit ...

which is solved by substituting our solutions for the two currents...

A little boring algebraic manipulation gives...

and a little more yields a more useful form for the "final" result...

This impedance is that of a series combination of resistor and inductor, with another resistor "shunting" the inductor, as shown in this equivalent circuit...

The Gyrator is seen to emulate a "virtual inductor" having value L = (R₂-R₁)R₁C, in series with a resistor R_s = R₁, shunted by a resistor R_shunt=R₂-R₁. This virtual inductor can easily have large value - a value so high as to be impractical to achieve using a physical inductor.

Simplistic descriptions of the Gyrator have an approximate solution for the "virtual inductor" (which is the same as that presented in my erroneous "analysis") but miss the shunt resistance. In practical cases, R₂ >> R₁, such that the simple solution is a very good approximation of the correct analysis presented here. But that's no excuse - an analysis (even one published in such informal surroundings as this blog) must be right.

QED Hi Hi

...-.- de m0xpd

Slightly more organized

2011-07-25T06:36:00.009+01:00

My work has been making unusually high intrusions into the more important aspects of life recently, with the pressures of moving to new premises and trips to The Netherlands and Italy in the last two weeks. Although little has been achieved in matters which might interest you, dear reader, I have at least been able to move slightly forward on the Virtual Organ (Blogs passim)...

Specifically, the organ has acquired another set of Hammond drawbars (giving me a full complement of 9 drawbars for each of the swell and great manuals), a dedicated PC and an old monitor.

This past weekend, I finally got round to transferring the main controller (in which a PIC16f873 reads all the drawbars and switches and sends their settings to the PC over MIDI) from a solderless breadboard to a couple of PCBs...

The main controller board still has a 16*2 display, which one day will move from the board to a visible position on the outer case of the organ. There is also a separate "decode" board, made to correct my own stupidity in not incorporating sufficient decoding on the drawbar interface boards (the action of which is described here), one of which is seen in the photo above.

Also visible in the photo are a couple of small boards which provide interface to assorted analog controls (at the moment, potentiometers for percussion and key-click level). These boards also interface to switches but this is a waste for simple "Boolean" controls - one day I'll use the matrix interface I've built into the new controller board to read the switch settings.

The photo below shows the organ in a corner of the shack, with the software running in the new small form factor PC I "won" on eBay just for this project.

The pedal-board "woodwork" needs completing - in fact the entire organ needs a new enclosure. Still - at least it is now working, playable and self-contained. Next task is to sort out the bug in the new PC which is making it very difficult to turn on (without apparently random resets, visits to "Safe Mode" etc). Perhaps I should have relied on traditional tone-wheel technology rather than a computer!

...-.- de m0xpd

Bit Set - or not

2011-07-17T15:50:00.008+01:00

I've been playing with a simple PWM application on PICs...

The final application will use an 8-pin PIC (the 12F675) but I chose to start code development on the 16F676, partly because I had some in the junk bin and mainly because I also had the special 20-pin PIC16F676-ICD device which allowed me to do debugging (I'm too cheap to buy the PIC12F675-ICD).

All was working FB until I tried to translate the code to the 12F675 - I had one of my two PWM signals running, but couldn't get the second to appear on the appropriate I/O line, no matter what I tried.

Here's what turned out to be the offending lines of code...

It is part of the interrupt service routine, which establishes the two (phase-opposed) PWM signals on GPIO pins 1 and 2. The signal on GPIO2 was fine, but there was nothing but a glitch on GPIO1.

Can you see anything wrong with the code? I couldn't - despite staring at it for an hour!

I assumed that I'd made a mess of setting up the GPIO port and spent ages staring at different pieces of the program and making changes just out of desperation. Everything appeared logically consistent and I just couldn't see where I'd gone wrong.

Eventually, I searched for anybody else who'd suffered the indignity of PICs behaving badly.

Fortunately some Kiwis have trodden this path before me and written it up .

It seems you can't just perform bit-wise operations (like bit-set or bit-clear) on the port of the 12F675 without errors (perhaps I should say without "unexpected results"), despite the fact that you can on other PICs - like the 16F676 on which I did my code development!

The fix is simple - don't use bit-wise manipulations...

I feel a little better that I couldn't see a logical error in the code (there wasn't one) but the fact that the 12F675 "doesn't obey its own instructions" still galls!

...-.- de m0xpd

Gyrator analysis

2011-07-05T18:09:00.017+01:00

Your humble servant's article in this spring's number of SPRAT (pp 20 - 23), "A(nother) CW Filter", uses a circuit called a Gyrator to implement an inductive impedance. I was thinking ahead to a scheduled talk on the CW Filter at the Warrington club and realized it would be nice (that is to say "it would please me") to include an analysis of the gyrator.

This is a pretty standard circuit configuration, but a quick Google ((v) search the internet (for information) using the Google search engine) revealed that such analyses aren't exactly falling over one another - so here's the m0xpd story...

The circuit in question is shown below...

The voltage at the non-inverting input to the op-amp is related to the input voltage by the potential divider equation:

Ideal action of the op-amp (which is configured as a voltage follower) is summarised by:

We're now in a position to identify the currents i₁ and i₂ - we start with i₁...

Substituting for the voltage at the non-inverting input gives (with apologies for the contribution of the "Microsoft Equation 3.0" equation editor):

i₂ is simpler:

The input impedance to the circuit is:

which is solved by substituting for the two currents above...

There (in the box) it is!

The input impedance is the series combination of a resistor and a "virtual" inductor (in the sense that an inductor presents a positive reactance, proportional to frequency), with the inductor taking the value of the product of the two resistances and the capacitance...

Next time you need a big coil, try one of these instead!

...-.- de m0xpd

That's just swell

2011-06-17T18:41:00.012+01:00

A few otherwise idle moments were used fitting the swell / expression pedal from the old Hammond Organ Donor into my virtual organ project (Blogs passim).

Here's the swell pedal, complete with a nice patina of rust...

I put out a cri-de-coeur a few weeks back in this blog and on the Organ Forum, asking for any information on Hammond Swell pedals, but attracted a null response. Fortunately a new Texan friend gave me some advice and put me on the right track.

The pedal has a light source (an ordinary incandescent bulb) and a light-dependant resistor. There is a tapered shutter (implemented on a piece of fibreglass PCB) which moves with the pedal and stops down the light reaching the LDR. The key components are visible here...

I tried to measure the resistance of the unit as a function of pedal angle - with mixed results. Here's a graph, which reveals an approximately logarithmic taper (as you might expect, given that the pedal originally implemented an audio volume control function). Unfortunately, the resistance went out of range of the meter I used as I got close to the 0 degrees (i.e. fully depressed) position. Still, the graph has taught us its lesson...

I originally had planned to connect the pedal to one of the analog inputs implemented on the main controller - but it occurred to me that I could interface to the separate pedal controller instead.

This had the advantage of physical proximity to the swell pedal, making a completely stand-alone pedal unit. The disadvantage was the fact that the pedal controller had, to date, no existing analog interface. What's more, the only available I/O line on the PIC 16F676 was not one of those that could be set up as an analog input. Accordingly, I had to make a complete re-work of the pedal controller. This gave me chance to add a stabilized power supply for the swell pedal's bulb (which draws about 180 mA at the 5V operating point I've chosen).

Here's a schematic of the revised pedal controller...

and here's the finished system (with the bulb regulator sporting an old TO3 heatsink from the junkbox)...

You can see the additional connectors to provide power to the bulb and to sense the pedal resistance.

It works very well - but the logarithmic taper makes the expression control (too) non-linear. I need to implement a look-up table in the software to undo the log taper - but that will have to wait until the next otherwise idle moment!

...-.- de m0xpd

SSDRA, another Dipper, and Red Roses

2011-06-05T14:37:00.007+01:00

EUREKA - I have found a copy of Solid State Design for the Radio Amateur - for just a pound!

I spent an hour at West Manchester's Annual "Red Rose" QRP Rally today - which is where I made my purchase of the classic by Hayward and DeMaw. It is a paperback edition and it is a little tatty - but complete. A genuine bargain!

On the same stall, I spotted another Dipper, which I snapped up (this time for four pounds), thinking I might use the coils with the Heathkit unit I won in a WARC raffle a few weeks back.

However, on testing the device, I found it very sensitive, beating both my g3wpo and my GD-1u raffle win, so I shalln't be stealing away the coils.

Here's the new dipper...

It is powered by a PP3, has one active device (a four-pin metal can carrying the (partial) number 2089 - or is it 7089) which I don't recognise and is either an excellent piece of homebrew or a nicely executed kit. There are no identifying marks of any kind - so if you can tell me anything about it, I'd love to know!

I replenished stocks of some boring items from Will at Bowood, stopped by at the Kanga, RSGB and (of course) G-QRP stalls and took my leave of this excellent rally. I will certainly return next year and encourage all within striking distance to do the same.

...-.- de m0xpd

m0xpd/mm

2011-06-04T09:55:00.017+01:00

Just back from a(nother) sailing trip on the Westerly Discus CC sloop "Beatrice Rose", with owner Neil and fellow crew member Paul...

This voyage took us from Beatrice Rose's home port of Southsea Marina to Lymington, Poole, Portland, Yarmouth, Newtown Creek, Folly Reach (R. Medina) and back to Southsea. We logged 195 miles, 95% of which was sailing close-hauled to windward.

The opening weekend saw foul weather (in which an 11m yacht was lost), some of which we sat out for a day in Lymington after becoming bored beating into a Force 7 through the Solent. During that enforced rest, I took out the FT817 in the hope of making some CW QSOs as m0xpd/mm, but discovered that Berthon, Lymington (in common with most other marinas) is QRM hell (there are lots of noisy inverters etc on boats) and 40m was s9 +10dB of solid, ugly noise.

VERY unusually, I had also packed the FT817's microphone, so I switched to 2 metres and answered a shout from Rob, g6bdv. Rob was on a cliff-top above the Needles (the conspicuous rocks at the western tip of the Isle of Wight) and reported 50 miles-an-hour wind gusts at that exposed location. Here's a photo of Rob's location which I took a few days later as we passed on our (engine assisted) run east from Portland - in rather calmer conditions!

We shared Poole Quay with a pretty brace of tall ships: the Sea Cadets' Training Ship "Royalist"...

and another brig, "Øilleleje"...

Later, after a night in the new marina associated with next year's Olympic sailing events at Portland and a visit to Yarmouth, which was appropriately dressed for the visit of the Old Gaffers this weekend...

we spent a night on a buoy in the idyllic Newtown Creek (here seen with shoal draft boats moored close to the "Conspicuous Black Boathouse")...

At last, I had escaped the buzz and drone of the boaties' QRM and could enjoy some real (i.e. CW) QSOs - most notably with Fred, dl4zby, nr Frankfurt.

A terrific trip - which landed me back ashore in time for tomorrow's Red Rose QRP Festival. Thanks, Neil!

...-.- de m0xpd(/mm)

Additive Fourier Synthesis

2011-05-22T11:44:00.019+01:00

Regular readers (poor things!) might recall that I won a genuine set of Hammond Drawbars on eBay (originally salvaged from a Hammond L100 donor organ)...

I've already explained that "drawbars are gain controls for individual harmonic components" - allow me to be a little more precise...

The nine drawbars in a "set" give partial control over the elements of two harmonic series; one series built on the fundamental (which is associated with the "8 foot" drawbar - the "foot" dimension being a legacy of pipe organs) and the other built on the sub-harmonic an octave below that fundamental. Of course, the fundamental changes with each key that is depressed - but if you imagine we're depressing only "middle C", the following picture is worth several lines of my boring words...

Notice from my graphic that the sub-harmonic series' drawbars are coloured brown, those which sound the same note (in terms of tonic sol-fah) as the fundamental are white, and other elements of the series are black. You will also notice that the seventh harmonic is absent (as it is a de-tuned minor seventh which doesn't sound so good!). Anyway - enough music for the moment - let's get back to some electronics.

The drawbars are a series of multi-way switches, in which each drawbar has a contact able to touch some of seventeen commoned bus bars. The size of the contact is such that two busbars are contacted at any time, avoiding open-circuits during movement. In original use, the busbars were connected using a resistance network, making a series of stepped resistors.

The resistor network was implemented using resistance wire, and the lengths of these wires (proportional to the resistances) reveals that it is a non-linear ladder. The resistance wires were still in place in my unit from eBay...

My interface had been developed for use with a series of potentiometers...

... but this wouldn't work with the drawbars. I had to re-interpret to work with the "multi-way" switches. Fortunately, the change was minor - you can see one drawbar's worth of circuit here, with the common block inherited from the "potentiometer" scheme above...

Notice that, as in the original Hammond organ from which these drawbars were harvested, I needed a resistor ladder. I designed the taper of this ladder to generate a voltage output proportional to the drawbar setting - this one was much higher impedance than the original ladder (by a factor of ~10000).

Here's the genuine Hammond drawbars in place...

and here's a screen-shot of the resulting settings in OrganizedTrio - EUREKA!

Bubbling over with success I went on to try to connect up a pedal drawbar (the L100 had only one (16') pedal drawbar) but hit a problem. The Organized Trio VST plugin doesn't allow external control of the pedal drawbars despite the claims of its documentation -

Oh well - it does sound good and the price certainly was right - cheapskates can't be choosers!

The absence of pedal drawbars left me with lots of "free" analog interface lines, which could be used to connect either analog (i.e. proportional) or "Boolean" (i.e. On/Off) controls. I had planned to do the latter with a separate "switch matrix" scheme, but opted for as simpler approach, using the analog interface, in which the potentiometer used for proportional controls was replaced by a spdt switch, to give "full-on" or "full-off" control...

Here's a temporary control solution, in which switches in the percussion and vibrato / chorus control sections have been implemented using toggle switches...

This gives me pretty much all the controllability of a B3 (bar the pedal drawbars and the restricted lower manual drawbars of the L100). Anybody know where I can buy nice soft action rocker keys???

In the course of adding these "Boolean" controls, I noticed another "funny" about Organized Trio. The percussion "On/Off" isn't a two-state control at all - in fact it is another "level" control, with proportional action. I wonder if the others are like this too.

That's all for now

...-.- de m0xpd

Dippers

2011-05-19T18:37:00.013+01:00

A couple of weeks back I won a Heathkit GD-1u Grid Dip Oscillator in the weekly raffle at Warrington A.R.C.

Yes - of course there are the usual raffle prizes - bottles of booze, packs of Kit-Kat - everything you'd expect from the best club (I am wearing my flame-proof suit). But, despite the temptations of beer and biscuits, I prefer to pick up the nice pieces of hardware occasionally on offer - and this dipper certainly is nice!

OK - there was a down-side...

The dipper came without any coils and the meter glass had collapsed onto the movement. A quick disassembly and some suitable glue soon sorted the meter and my friend Albert, g3zhe (who would be called my 'Elmer' if we lived on the other side of the pond) has loaned me his set of coils to copy. Here's one of them...

The coil set came in the nice original fitted box...

First thing I needed to do, having borrowed the cols, was test the dipper. I made up a resonant L-C network using a coil from my g3wpo FET dipper and a 1nF capacitor...

A quick estimate of the coil dimensions and a visit to an on-line coil impedance calculator suggested an inductance of 12.03 micro Henrys, giving an associated resonant frequency of 3.53 MHz.

Here's a video (YES - Shack Nasties is entering the video age!!) showing me tuning the dipper after placing the test resonant network next to the "Band A" coil chosen to place the Heathkit GDO in the correct band...

Here's the frequency dial setting associated with the dip...

The reading of 3.75MHz isn't a bad result given the tolerance of the capacitance and the crude estimate of inductance. To "double check", I tuned the g1wpo dipper, which gave the following result...

AMAZING! 3.75MHz (Scale "B" at the bottom of the photo) - these things actually work!

In fact, the old Heathkit dipper seems rather more sensitive than the g1wpo - here's a(nother) video clip, showing the Heathkit meter as I move the test resonator up to the coil...

The same effect on the g1wpo produces a rather less distinct "dip"...

All I have to do now is copy the coils for the Heathkit - no mean task - I'll tell you how I get on.

What a fantastic raffle prize - sure beats a packet of KitKats!

...-.- de m0xpd

Progress on the Virtual Organ

2011-05-07T14:58:00.014+01:00

Quite a volume of water has flowed under the bridge on the virtual organ project...

Firstly, the MIDI bass pedal electronics have been cast in stone (or, at least, cast on a small PCB)...

Next, I purchased a bunch of linear potentiometers from a trader on eBay, and made up a PCB to take nine of them (enough for a single manual). Here's the set...

Readers may recall that I've explained how my drawbars are scanned - but I needed to make up an interface (having previously only breadboarded the solution for 5 drawbars and a single additional analog control). I designed an interface to service a set of 9 drawbars and another set of 5. Two of these units will be needed - one for the swell manual & pedals and another for the great manual and miscellaneous analog controls.

Here's my schematic...

I elected to use the A733 PNP transistors I salvaged from the "Donor Organ" - not only as a signature "cheapskate" joke, but also to ensure that authentic Hammond sound!!!

Here's the finished unit, made up on some nice white PCB board I picked up at the NARSA rally...

So - here's a shot of the "organ" development to date (sans pedals, which are hiding out of view)...

You can even see the lunatic Leslie Switch!

I have the new drawbars AND the original 5 "test" drawbars running (the latter now configured for the lower manual).

Just as I finished the new set of "potentiometer" drawbars, a genuine set of Hammond drawbars came up on eBay. I snapped them up and will be fitting them to this project. Real drawbars are nine-position switches (rather than potentiometers), so an entirely new interface methodology will be required - but it have been fun developing this one (and I can still use it to implement general analog controls).

Watch this space to see the real Drawbars.

...-.- de m0xpd

The COMMONER Beacon

2011-05-07T08:35:00.014+01:00

After a week of fairy-tale operation with the Royal secondary locator, my multi-mode beacon (Blogs passim) has reverted to type and abdicated the Royal moniker.

The mr0xpd beacon's FSKCW and S/MT Hellschreiber modes usually were visible on Johnan, on5ex's grabber in Zevergem, Belgium...

but the best reported QRSS performance was the 2706.6 miles to Nova Scotia, where loyal Knight Vernon, ve1vdm, reported seeing "MR0XPD - still at the wedding LOL!!!"

(In fact, you can just see the closing "pd" of the royal FSKCW call and the opening "mr" - look just above the QRM at 7000808Hz - the S/MT Hell is faintly visible, but only if you know where to look!).

The WSPR emissions were spotted in the US several times, including in Illinois by Steven, k9an...

in Michigan by David, w8fgu...

and in New York by Daniel, kc2sta and Craig, kc2lfi...

Having abandoned the royal status, the commoner beacon was immediately spotted this morning on WSPR...

and is now back on Johan's Belgian QRSS grabber.

The Notice-of-Variation is valid until Monday, but this marks the end of all my "Royal" beacon working,

...-.- de m0xpd

The Balcony Kiss(es)

2011-04-29T13:19:00.010+01:00

The final staged events of this unusual day played out at Buck House, climaxing with a fly-past from the Royal Air Force ...

including the Battle of Britain Memorial Flight, as previously reported on these pages, and the traditional public kiss, updated this time to TWO kisses (the first having been too brief to satisfy)...

Perhaps life can return to normal now!

...-.- de mr0xpd

The Bells Ring Out!

2011-04-29T12:08:00.008+01:00

As the Happy Couple emerge...

... propagation to on5ex's QRSS grabber in Zevergem, Belgium JO10ux, droops somewhat (though fellow Warrington royalist, gr4vss, is still ringing out his peals of celebration as far as Belgium).

...-.- de mr0xpd

Let no man put asunder...

2011-04-29T11:19:00.004+01:00

The solemnization of matrimony is under way, with Rowan at the helm...

Simultaneously, the multi-mode beacon is being received, including by Luc, on7kb, who reports reception of the WSPR emissions at the moment of solemnization.

...-.- de mr0xpd

Beacon by Royal Appointment

2011-04-29T10:18:00.004+01:00

Today, the multi-mode beacon (Blogs passim) is proudly waving the "mr0xpd" flag on 40m - all reception reports gratefully received.

Latest News from Westminster:- Her Madge and Phil the Greek have bolted down their Shredded Wheat(s) and are ready for the ceremony...

...-.- de mr0xpd

mr0xpd and THAT Dress

2011-04-29T07:20:00.006+01:00

British Hams have been given the opportunity (WHY ?!?!) to apply for a "Notice of Variation" to their license, allowing the secondary locator "R" (for Royal) to be used, in "celebration" of The Royal Wedding. So, today and for the next few days I am become mr0xpd - deep joy!

Just for the record, I am mildly pro-monarchy (although by nature I am more comfortable in Roundhead garb than the lacy, foppish excess of the Cavaliers and The Oxford Movement).

In addition to the exciting news of the call sign, I am able to bring you a special scoop from the paparazzi - pictures of THAT Dress, fully two hours before the rest of the world's media.

Here's Kate...

Doesn't she look radiant!

More news to follow throughout the day,

...-.- de mR0xpd HI HI

H/B WSPR Rx

2011-04-23T17:47:00.008+01:00

I found an ABS box in "stores" and put the pa0klt VFO kit into it...

Stores didn't have a dc socket in stock, so power currently passes through a hole in the case. I opted to leave out the LCD backlight as my contribution to measures to slow down climate change!

I decided to try out the new VFO by using it to drive my WSPR receiver module, seen here on the bench with a bandpass filter (which previously featured in the multi-mode beacon until it was rendered obsolete by the arrival of the multi-band bandpass) in the antenna path. This allowed me to run the receiver on 30m whilst the multi-mode beacon was transmitting on 40m (without it, the "open" front end of the direct conversion receiver was swamped by the transmitter output).

It was nice to do some WSPR receiving again - something of a payback for all those times I've been just transmitting! Here's the decode screen doing its stuff...

But the real beauty was running a h/b WSPR receiver whilst simultaneously working mu h/b multi-mode beacon. Here's a map showing a snapshot of both Rx on 30m and Tx on 40...

Great fun - I think I'll make some kind of box for the receiver system next.

...-.- de m0xpd

pa0klt VFO Synth

2011-04-22T11:59:00.010+01:00

Last year at the G-QRP Mini-Convention I purchased a VFO synth kit from fellow sailing enthusiast Jan, g0bbl at SDR-Kits. The system was designed by Ton, pa0klt and uses the same Si570 used in my beacon's DDS to make a very nice, flexible, fully-featured synthesizer. Today I decided it was about time to make up the kit...

Like all Jan's kits, the quality, presentation and instructions are exemplary and it didn't take more than a couple of hours to assemble.

Here's the completed board, showing the Si570 (lower right), the controlling ATMEGA88 and the conspicuous connectors which interface to the display, the switch array and the all-important rotary encoder...

There are a number of surface-mount capacitors in the kit which, together with the Si570, will be a challenge for anybody used only to leaded, through-hole components. However - as I've said before, if I can do it (with my imperfect vision, intention tremor and general cack-handedness) anybody can. Don't be put off - give it a go.

Here's the underside of the board, on which some of the SM capacitors are visible...

I knocked up a temporary set of switches, connected the rotary encoder and plugged it all together on the desk for a test flight - worked perfectly...

This is a great kit and an elegantly designed and executed system - thanks to both Jan and Ton.

Now all I need is to put it in an enclosure - a perfect Bank Holiday Weekend project!

...-.- de m0xpd

g1dva Beacon Reports

2011-04-21T18:34:00.014+01:00

Well - I got a replacement crystal for my g1dva QRSS beacon (thanks Dennis!) and put it on the air last night via my 1/2 g5rv with inductors and extensions for 80m...

I'm afraid I announced the event with an error on KnightsQRSS. I had my rig in CW mode when setting up, rather than USB - so I had accidentally included the CW offset. Don't tell anybody, but I think I may have squirted out some RF below the 80m band before realising my dumb mistake and tuning to 3.50002 MHz! Anyway, despite the bum steer on QRG, the Knights soon tracked me down and the reports came in...

First to arrive was a report from fellow FISTS member, Paul, m0bmn in Wolverhampton. I had met Paul at the NARSA rally a couple of weeks back where, like me, he purchased a g1dva beacon kit from Kanga (m0bmn's beacon is on 40m).

Maik, dl4dtl, kindly put his 'part-time' QRSS grabber onto 80m for the night in an attempt to copy me in JN49IH, South Germany. I captured a screen shot of my signal (both FSKCW and CW) on Maik's grabber...

and Maik kindly sent what he thought was the best grab of the night...

The 80m QRSS band segment certainly seems less densely populated than 30 and 40!

Les, g3vyz, sent images of my CW...

and FSKCW...

received at his QTH in Whitley Bay.

Keith, g6nhu, who also runs an occasional QRSS Grabber spotted me in Essex...

and Steen Erik, LA5GOA, confirmed that my signal was "clear and readable in jo29oi".

Many thanks to all who sent in reception reports - the g1dva beacon is now off-air and I'm back to my multi-mode beacon (Blogs passim), which currently is struttin' its stuff on 40m.

...-.- de m0xpd

g1dva Beacon Kit

2011-04-17T14:27:00.012+01:00

Having splashed out on a g1dva beacon kit from Kanga-UK last weekend at the NARSA rally, I thought it would be politic to make it before seeing the man himself at our WARC meeting on Tuesday...

The build instructions are available from the Kanga website. I followed them and ended up with a working beacon - but not until I realized that the crystal was dead. I've never killed a crystal before by soldering it in place, but I guess there's a first time for everything.

Here's the made-up kit (now sporting a socket for the xtal and a temporary 3.579... colour-burst crystal for testing)

The beacon worked first time (second time, if you count the dead crystal), announcing its presence with a QRQ version of my call (note to self: that's a good idea - must work it into the multi-mode beacon). Here's the FSKCW signal from the beacon, locally captured...

Here's the QRSS CW output too...

I guess (given similar experience with my own beacons) that a small enclosure will help the frequency stability.

Once I have a replacement 3.5 MHz crystal, I'll put the beacon on the air and tell you of any reception reports.

...-.- de m0xpd

Another Birthday in Blackpool

2011-04-13T18:26:00.012+01:00

Rushed back from holiday to participate in the annual NARSA Rally in Blackpool.

Regular readers may recall that this event marks the anniversary of my involvement in amateur radio.

This year, my multi-mode beacon (Blogs passim) was featured on the WARC stand. I made a transparent lid so the great unwashed could see in and I could keep their fingers out!

Here's the beacon in her tantalising see-through clothes...

Mike, g4vss, Paul, g1vda and I had worked up a QRSS theme for the Warrington display this year. Here's my beacon on the stand...

where she shared the limelight with the excellent new g1vda QRSS beacon kit, developed as a WARC project and now available from Kanga UK.

I dusted off the m0xpd wallet and got one of the beacon kits for 80m (chosen as my beacon won't operate on 80m). I also got a year's supply of single-sided, copper-clad fibreglass board at a great price and one of the Czech keys frequently advertised in SPRAT...

Of course, I chose to buy one of the cosmetically imperfect "B grade" keys at 25% discount. Despite the blemishes the key feels great - first QSO was with John, g4oyc.

My "Birthday Celebration" was crowned by finally meeting some people in the flesh who previously had been contacts at the end of various electronic links - very nice to meet you (you know who you are!)

...-.- de m0xpd

Pisces in Pickering

2011-04-13T18:10:00.005+01:00

Just back from the annual vernal "pilgrimage" to Whitby.

Apart from the usual delights, I enjoyed another day's fishing at Pickering Trout Lake, just at the end of the NYMR line. I landed thirty fish, on buzzers and goldheads, the best of which (in fact, the last of which) is seen here...

The top of the net frame is 24 inches wide...

so you see this was no minnow!

I took the FT817 and Walkabout whip and tried /p working from the east side of the harbour, emulating Juan, ea5blp's seaside exploits. Unfortunately, I didn't enjoy much success (perhaps due to being in the "shadow" of the nearby cliff, on top of which sits the Abbey) but I did enjoy a FB QRP chat with Tony, g3yho.

Happy Days,

...-.- de m0xpd

MIDI Bass Pedals

2011-03-29T17:01:00.014+01:00

The virtual organ project continues...

As I mentioned before, the key elements of the player interface for a virtual “Hammond-style” organ are...

• Keyboards
• Pedals
• Controls

The keyboards are cheap (and rather nasty) "off the shelf" items. I’ve demonstrated how to implement the controls (both simple Boolean controls and – most importantly – analog controls such as drawbars). Now it is time to confront the bass pedals.

Whilst a full-size RCO pedalboard would be nice (and remains on the wish-list for the future) a more practical 13-note pedal department will have to do for the moment. Whilst making one from scratch would be fun, there are only so many hours in the day and old organs (with perfectly serviceable pedals) are cheap.

I found such a cheap organ on eBay – won for the princely sum of a pound (pity about the diesel I burned in transporting it home).

Here is the “organ donor” – a Hammond 9422k, enjoying its last few moments in the “old keyboards’ home” next to my Fender Rhodes...

Unlike the other kind of organ donor scheme (in which – as I heard on the radio recently - the donor is left for five minutes after their heart stops – just in case), this donor was still viable. It worked. That is to say, whilst 95% of all the voices sounded dreadfully “70’s home organ” and were an insult to the name “Hammond”, I could use it to perform (at best) a parody of a Rive Gauche Cafe Accordionist. Accordingly, I admit to feeling a twinge of guilt when I broke it up for “transplant”.

I’ve saved the Leslie, the main speaker, the amplifier and the control electronics to select between them. I’ve saved the manuals (which feel so much better than my MIDI controller keyboards). I’ve salvaged several miles of hook-up wire and several dozen A733 PNP transistors. Most importantly, I salvaged a nice set of pedals (see here atop the old Workmate)...

Now – how to interface this array of switches...

I have some experience of arranging an intimate relationship between a PIC and a switch array (not least in the keypad for my multi-mode beacon). Here, I decided to use the same strategy – a group of four input lines with pull-down resistors, any of which can be pulled high by closing one of the pedal switches (you can see the 13 nice microswitches in the photo above). The switches would be addressed in groups of 4, requiring 4 “groups” to cover the 13 switches.

I created these addressable groups using a 3 – 8 line demultiplexer chip (to lower the burden on PIC I/O lines). This approach “future-proofs” the design, to allow expansion to a 2-octave (25 key) pedal board in the future.

I could have added to the program already running in the PIC16F873 which controls my drawbars – but I decided against this for several reasons...
• Wiring complexity between pedals and the console
• Saving code space, time and I/O pins on the PIC16F873
• Availability of lots of 14 pin PICF676’s in the junk box
• Production of a stand-alone solution for others to copy

Accordingly, here’s my design for a solution based on the PIC 16F676...

The pedals connect to the jumpers at bottom right of the schematic above like this...

OK – hardware is easy enough – now for the software...

The current “state” of the switches is read into two 8-bit registers “Pedals1” and “Pedals2”. This code segment shows scanning 8 keys into "Pedals1"...

These states are compared with the previous states, held in the registers imaginatively named “OldPedals1” and “OldPedals2”. Here’s the comparison for the first state register...

If there is a change between “Pedals1” and “OldPedals1” (signalled by one or more bits asserted in “DeltaP1”) the code above calls the subroutine “P1Change”...

Any asserted bit in “DeltaP1” results in a call to the relevant note subroutine – as, for example, the subroutine for the bottom C (which calls Ross Bencina's "sendmidi" subroutine via the macros "Noteon" and "Noteoff")...

Note that the settings of OldPedals are only changed after the relevant MIDI command has been sent – when OldPedals indicates that a note is “on”, it really is on – and vice-versa!

The code gives full 13-note polyphony (I’m not sure if that is a help or a hindrance!) and works perfectly. In a next version, I’ll use the extra three available switches to allow me to transpose up or down an octave – maybe.

All that remained was to cobble together an enclosure for the pedals. Here’s my “Work-in-Progress”, made out of the veneered plywood which formed the top of the old donor organ...

The system includes the (optical) swell pedal from the donor. I need to find some information on this device before I can build its interface (a question on The Organ Forum has yielded nothing but deafening silence so far). If you know anything about Hammond optical swell pedals, please contact me.

A third MIDI-USB interface arrived in the post this morning – so I’m up-and-running with two manuals, pedals, drawbars, percussion level, Leslie switch... We’re getting there!

...-.- de m0xpd

Multi-Band LowPass

2011-03-24T17:53:00.012Z

The multi-mode beacon (Blogs passim) is scheduled to make her public debut in a few weeks time at the NARSA Blackpool rally. Like any débutante, she needs to look her best...

Amongst the many areas for development within the beacon, there is one gaping “incomplete” – the output lowpass filter. To date, I’ve been using the original ugly 30m lowpass seen in the photo below...

I had always planned to make a switchable output filter, after the style of the multi-band BandPass filter - indeed, I’d already provided a controlling output on the controller board and already written the code to switch bands. Now the time for the hardware finally had arrived...

Here’s the schematic – it borrows extensively from my BandPass system...

The board layout also exploits the work already done for the BandPass filter – all I had to do was change the central filter area. Here’s the resulting board, without any filter components fitted...

The filters used the design guide published by George Dobbs, g3rjv, which is derived from the work of Ed Wetherhold, w3nqn.

I made up the seventh-order filters specified for both 30 and 40m bands on the first two “channels” of the board...

The final channel is unpopulated (until such time as I decide which band to play with next), as with the BandPass unit. I may even go for a plug-in final filter, to keep my options open.

Here’s the new output filter in situ...

It works perfectly (now I’ve tracked down the accidental short on the output HI HI).

Any readers visiting the Blackpool Rally are encouraged to come and meet the beacon on the Warrington ARC stand (just inside the door, near the Bar – where else!)

...-.- de m0xpd

Semi Lunacy

2011-03-20T10:07:00.021Z

Visitors hoping to see the CW Filter project should click here

Well – the “virtual organ” project continues...

You might remember that I’m building some aspects of a physical interface for a “Hammond-style” tonewheel organ emulation (currently using the “Organzied Trio” VST plug-in). The first and most important part of the interface is undoubtedly the drawbars, but I’ve cracked that. Next on my list of “must-have” features is another iconic aspect of old Hammonds: the Leslie switch. Let me explain...

Hammond organs traditionally have been paired with “Leslie” loudspeakers within which sound is passed through rotating horns (or “baffles” for the lower frequency components). This system exploits Doppler shifts to generate interesting comb-filtering effects, the rate-of-change of which (corresponding to the speed of the rotating elements of the Leslie speaker) is controlled by a two (or three) position switch. In later organs, this switch was integrated within the console. However, perhaps as result of alleged antipathy between the Hammond and Leslie companies, early organs had an external switch fixed to the lower left side of the console, where the player conveniently could control it with her/his left hand.

That switch was mounted in a “half-moon” shaped case; the “semi lunacy” of our title is part of Hammond iconography (so much so there’s a crowd in the US trading as Halfmoon Electronics) and not another cheesy astronomical link to mark yesterday's lunar perigee.

Here’s one, mounted on a B3. Fortunately (for visibility) this one is white – more usually they were a sombre brown (the originals were made of Bakelite) or black.

I decided – in my lunacy – to make a half-moon enclosure for the switch I got from the good people at Warman Guitars (good prices, great service and a sense of humour).

I hacked a piece off some PVC 200mm soil pipe, glued on a “back” made of Perspex and roughed out a “top” from fibreglass PCB material (in which I cut the slot using a dental burr in my old horizontal milling machine).

Some more epoxy and fettling had the case finished...

The white “brackets” on the back are the "nylon" corner blocks that have replaced joinery skills in cheap modern furniture.

Here’s the whole shooting match installed on the temporary stand on which I'm assembling the "organ"...

All we need now is a lick of paint.

The switch grounds one of two PIC I/O lines which have pull-up resistors. The code reads these two I/O lines and sends MIDI commands to set the speed of the "Leslie" simulation accordingly. The switch currently selects between "Chorale" (slow; switch left) or "Tremolo" (fast; switch right). I've left the central position inactive (it should stop the Leslie rotors completely, but the Organized Trio software makes an irritating glitch when you de-select the Leslie simulation, so I've left it out).

Next step is the pedals – I’ve just won an old wrecker Hammond on eBay, from which I’ll rob out the pedal assembly and, perhaps, a few other bits. These will be converted to MIDI operation after even more coding for the PIC16F873.

Watch this space!

...-.- de m0xpd

A(nother) CW Filter

2011-03-18T18:15:00.012Z

I have held this subject under a self-imposed “D-Notice” for the past few months as George, g3rjv, kindly agreed to publish it in our beloved SPRAT. Today, the Spring 2011 number hit my doormat, with my article on page 20, so I feel free to comment...

There have been any number of attempts to limit the output bandwidth of a CW receiver “correctly” (i.e. early in the signal chain) or as an “afterthought” (i.e. in the audio path). This idea belongs to the latter category. It is a tunable bandpass filter, which I designed with the intention of providing independent control of tuning and bandwidth. The “novelty” of the design – if it has any – is associated with the application of a “gryrator”, which is used to emulate an inductor, and with the manner by which the bandwidth control is achieved.

The “virtual” inductor is resonated with a capacitor to produce a resonant system, tuned to the desired frequency. The bandwidth is established by driving the parallel “LC” network with controllable source impedance; high impedance drive gives a very narrow bandwidth and vice-versa. The SPRAT article gives more detail.

The original development version was the usual pig’s breakfast of tangled, blue spaghetti, as seen in the photo...

Despite the mess, I was sufficiently encouraged by the performance of the filter to write it up for the journal. Here’s the measured frequency response – bold lines show the response with R4 at extreme settings and dashed/dotted lines at manually selected intermediate settings of the R4 potentiometer.

It worked – but it was hardly suitable for everyday use, so I cooked up a more practical version...

Here’s the schematic (identical to that in SPRAT, except for the addition of a “bypass” switch, S1)

here’s a PCB layout ...

and here's the copper side (shown in negative to make it visible against the black background of this blog)...

(any reader foolish enough to reproduce this PCB can scale and invert using image handling software)

The twin-gang potentiometer was chosen from Maplin’s catalog (usual disclaimer) to ensure availability (part number JM84F ) – no doubt an equivalent part is available from “other fine retailers”!

Here’s the finished article...

The tuning control, R6, is reduced to a trimmer. Once set (to 600 Hz, in my case) it is left alone.

The unit sits on the shelf next to my Funster Plus 40m rig, the usability of which it greatly enhances.

One day, I’ll get round to building it into the Funster’s case (assuming it will fit)!

Now for the bad news...

I explained in the SPRAT article how the prototype system makes an ugly noise if you turn it on with the control in “narrowest bandwidth” setting (momentarily backing off R4 stops the oscillation, after which the unit can be used without further problem). When I made the PCB version (above) I noticed some more “issues”...

Don’t drop the power supply voltage to 9V – keep it at 12, or higher

Don’t overdrive the unit with incoming audio – too much signal will cause the unit to clip and distort (as the gyrator saturates)

One particular setting of R4 on the current PCB version (close to – but not at – the “widest bandwidth” setting) can also evoke a brief “buzz”/”fart” sound

Despite these practical challenges, the unit works very well in a QSO. So well that I’m not inclined to sort out the remaining bugs and issues – life is short and there are so many interesting things to do!

...-.- de m0xpd

MIDI Organ Drawbars

2011-03-12T17:19:00.054Z

Here's a pretty story about PIC interfacing. OK - so the context is music technology - but I think Hams and "Knack Victims" will find something of interest. Read on...

Regular readers will remember I was given a Digital Effects Processor as a Christmas present. I was amused to hear that one of my fellow members of WARC uses these processors in his shack! I think he uses something called a "microphone" as an input to his radios - 'nuff sed. Of course, I'm pretty fussy about audio quality, too - having gone to elaborate lengths to generate a nice sound!

The Processor has some old-school 5-pin DIN sockets on the back (reminiscent of those on my beloved old Quad 33 pre-amp), supporting something called MIDI; the "Musical Instrument Digital Interface".

Well, I've managed to get through half a century without MIDI (despite a lifelong interest and activity in music and electronics). However, prompted by those sockets on the back of my Christmas present, I decided it was high time I learned something about it.

A sniff around the web showed me it is easy to generate MIDI signals using a PIC. I cut my teeth with a program for the PIC 16F873, generating control signals for the Behringer processor - all pretty easy stuff.

MIDI's physical layer involves the 5-pin DIN connectors mentioned previously - so I added to my stable of PlugIn modules with a MIDI connector...

The socket was part of the bargain haul from g4vap's stand at the Red Rose Rally a few months back.

Having seen how easy MIDI is to generate, I started to think about a project that has been fermenting in the back of my mind for several years - an organ. Not the "Hauptwerk" PC-based emulations of pipe organs (though, no doubt, I'll end up running that too). Rather, a virtual "tonewheel" organ, emulating a Hammond - such as that played by several of my "heros"...

PC software emulating a Hammond was led by Native Instruments' "B4" software, a demo of which I downloaded a few years back. The "B4" software was impressive, but limited by the price tag for the code itself (far too rich for a cheapskate like me) and by the requirement for an expensive hardware interface for the player, including...

Keyboard(s)
Pedals
Controls

MIDI keyboards are cheap, but both pedals and controllers (especially organ-specific controllers) are VERY expensive. However, now I had cracked MIDI, I could consider homebrew controls and pedals...

The key to the control interface for a Hammond organ is the array of "Drawbars" (some of which are seen in the image above, sandwiched between Joey and Thijs).

For the non-musos, drawbars are gain controls for individual harmonic components of the sound produced by the organ. The Hammond Organ (at least, any one of the bigger models) provides 9 drawbars for each of the two manuals and a further 5 drawbars for the pedal department. That's 23 potentiometers - easy enough to handle in the original analog "mixing" context but a non-trivial interfacing problem in a digital emulation.

The PIC16F873, as used in the controller for my multi-mode beacon, has 5 channels of 10-bit Analog to Digital Conversion on-chip - but interface to 23 pots was going to need some kind of multiplexing scheme...

Obviously, trying to switch 23 individual analog voltages to one (or more) analog inputs would be a chore - so I decided that it would be simpler to switch the voltage applied to the "top" of each of the potentiometers sequentially, such that only one pot is "energized" at any instant. Diodes would block the inactive potentiometers, allowing a SINGLE ADC channel to read the selected drawbar. I could scan along all the controls and send a MIDI signal whenever a control setting is changed.

Here's a schematic of the idea, for the 9 drawbars of the upper manual ...

A four-bit "address bus" gives access to 15 individual controls (the last of the 16 states is used to generate an "off" condition) - enough for the upper manual drawbars plus some extra analog controls (swell pedal, etc) OR for the drawbars for the lower manual and the pedals. The "address bus" will be shared by these two units - selection between them is arranged by individual (active low) "latch enables".

Here's the code for reading the setting of a single Drawbar...

MIDI control values are 7-bit numbers (0:127) and I ignore changes in the bottom two bits when checking if a drawbar setting has changed.

The subroutine calls in the code segment above are all pretty trivial; "Latch_Upper" simply puts an (active low) pulse to the 74HC137s in the Upper Manual Drawbar unit, "Delay" "does what it says on the tin", "sendmidi" is Ross Bencina's routine and "ad_conv" drives the A->D conversion on the PIC's RA0 pin...

I've breadboarded the system with the only two slider potentiometers I had in the "junk box"...

It operates though a dirt-cheap MIDI - USB adapter, available for peanuts from many sellers on eBay...

(OK: the MIDI -> USB interface is difficult to get running until you find the right links on the 'net and pluck up the courage to make the necessary Registry Changes - but the price is right!).

The prototype works perfectly with the excellent Organized Trio VST plug-in (which is a free-ware version of VB3)...

All that remains is to buy 23 sliders - another "trip" to eBay is indicated!

...-.- de m0xpd

Update

I happened to swing by Maplins yesterday and couldn't resist buying up all their stock of sliders - which now adds up to the spectacular total of five! Here they are in a test lash-up with a couple of keyboards [they are mapped to the lowest five Upper (swell) manual drawbars]...

Even this level of controllability makes the organ emulator infinitely more usable and musical - great fun!

New Controller Board

2011-02-19T16:39:00.011Z

Having confirmed operation of the divider scheme on the output of the multi-mode beacon's Si570 local oscillator, I set about making a new controller board.

The new board shared most of the features (and PCB layout) of the old version, adding only the divide chain (using the old TTL chip) and control for the BandPass filter. To date, I had set the BandPass board up by manually setting the band select lines and pulling down the "chip enable" to latch the address (corresponding to the desired band) into the (74LS137) de-multiplexer. Now, I could arrange for the PIC16F873 to do all the hard work for me!

Here's the new board...

You can see the Si570 "piggy-back" surface mount board and the new divider network (with a jumper to select divide by 2 or 4). I also up-rated the power supply arrangements by substituting a 7805 for the 78L05 that was on the original controller. The two four-way headers at the bottom of the image provide ground, two select lines and an enable for the BandPass and a switchable output LowPass (when I finally get round to building it).

Here's the new board in situ...

A few more lines of code were written and now there's a satisfying "clunk" from the relays every time I change band.

Operation confirmed by my first spot after the mods - this time from Erich, dk6ug...

Now I shall be able to flip back and forth between bands with laughable ease (as the great H E L Falkus used to say).

...-.- de m0xpd

Multi-Band Reception Reports

2011-02-17T18:13:00.024Z

The multi-mode, multi-band beacon (Blogs passim) has been running continually since I added the frequency divider on the local oscillator. I started up on 40 metres and got pleasing reports...

Jan, pa9qv, who previously had spotted me "upside down" on 40 metres, now saw my QRSS and S/MT Hell the right way up...

Johan, on5ex, who also was used to seeing me upside down, was consistently showing my righted signals on his fine grabber site...

I was also pleased to be received by Joachim, pa1gsj, who originally suggested the idea of adding a frequency divider to my Si570 DDS...

I was fortunate that Pavel, ok2bma, was just beginning experiments with QRSS reception when he came across my signals - Pavel was kind enough to email from the Czech Republic with a reception report...

All the time these QRSS reports were coming in, the WSPR mode also was being received on 40m, with best DX to arctic Norway...

After all this successful performance on 40m I switched back to 30m - so nice to do that with the push of a button!

Maik, dl4dtl reported my signal on 40m before the switch (here you just see the closing ' d ' of my call in Hellschreiber followed by my call in FSKCW)...

and after the switch on 30m...

I now have made the PCB for an up-dated version of the controller board, with integral frequency divider (now selectable between divide by 2 and divide by 4 just in case I decide to give 80m a try) and with additional outputs to control the bandpass filter board and a switchable low pass filter (if I ever get round to making one). More details on that to follow.

In the meantime, many thanks to all those who have reported reception of my various signals on various bands!

...-.- de m0xpd

Inadequate User Manuals

2011-02-15T19:19:00.010Z

Well - my purchase of a new telescope has been the kiss of death for clear skies over the North West of England. However, last evening I managed to get outdoors for a few minutes...

I've been very pleased with the optical performance of the new Skyliner-200P FlexTube AUTO, but very disappointed with the tracking function - I couldn't get it to track at all.

I thought about the geometry involved and what must be going on inside the telescope's control system and realized that it was necessary for the telescope to know where it is pointing in azimuth to have any chance of tracking. I searched around on the internet, eventually finding an owner's manual for a scope from the same manufacturer (SkyWatcher) with a tracking AZ mount (which shares the same controller). That manual said you have to power up the 'scope with the tube facing North, thereby creating a known azimuth reference (my manual mentions NOTHING about that).

I tried that last night - and it still didn't work.

At the same time as realizing that the scope needs to know which way it is facing in AZ to be able to track, I recognized that it also needs to know where it is pointing in EL - but I had assumed that it has absolute angular sensing in EL (the elevation axis is limited in range and has an angle scale marked on the mount)...

After the "pointing North doesn't work" failure last evening, I wondered if the angular sensing in EL also needs a start reference (i.e. if the EL angular encoder is relative) and remembered reading (in the manuals for the other scopes) descriptions of powering up facing North AND with the tube at 0 degrees EL - the "home" position.

I tried that and - hey presto - tracking!

This is awful - there is absolutely no mention of this in the manual. OK - so I can figure it out, but what about all the other poor sods who buy one? Of course, we can pretend that anybody who wants a tracking 200mm telescope enough to buy one would be smart enough to figure out how to operate it despite the handicaps that "User Manuals" represent. The cynic (not to mention the realist) in me doubts that is true.

The fact is the manual is a disastrous "cut-and-paste" of segments from manuals for other products which, together, does not add up to a complete statement of how this device ought to work. Caveat emptor.

Having gotten that off my chest, I must say how very pleased I've been with the limited observations we've made so far. Obviously, looking at the moon is child's play - here's the result of my first experiment with the webcam adapter I got from my cousin at Sky's the Limit and a throw-away webcam...

The image was taken before I figured the tracking issue (above) and before I learned how to drive RegiStax, so I hope to do better in future!

Also, views of Jupiter have been stunning (until it sinks under my neighbour's garage) and the Great Nebula in Orion, m42, has been amazing too (once I got my bearings by figuring out I was splitting wide open the trapezium, theta-1 Orionis, even at lowest magnification). Now I'm waiting for Saturn to get its act together and appear higher in the sky at a decent hour (later this month / early next).

Why - I might even be able to track it!

...-.- de m0xpd

Upright Multi-Mode on 40

2011-02-05T18:01:00.015Z

After the recent inverted fun-and-games, today I have my beacon running on 40 meters - in all three modes...

I followed Joachim, pa1gsj's sensible suggestion simply to divide down my DDS oscillator output (derived from the Si570) in order to place it within the right ball-park for 40m operation. I had a 7474 double D-type flip-flop in the junk box, so I pressed that into service to make a divide-by-two stage. I figured the old TTL device's output would be able to drive the mixer well enough. Here's the additional sub-system, which I knocked up on Veroboard...

After some messing around with tuning, made complicated by the spacing between the WSPR and QRSS sub-bands on 40m (they're almost adjacent on 30m - so close that I can QSY using the VXO - on 40m I have to actually change the DDS frequency between modes), I had the CW and S/MT Hell outputs running "right side up" (unlike last time). Here's a locally captured grab...

At once, the WSPR emissions evidently were on target - here's the first spot, reported by Jorgen, oz7it...

I would be very grateful for further reports / spots.

Tomorrow I'll add a frequency doubling to all my 30m DDS settings to undo the action of the new frequency divider!

...-.- de m0xpd

m0xpd Observatory

2011-01-29T16:00:00.019Z

After many years avoiding the issue, today I finally dipped my toes into the world of amateur astronomy...

I guess it really started a few weeks ago when I got a Planisphere (after seeing it on the one of the BBC Stargazing Live programmes). I was blown away by the beautiful simplicity of the Planisphere, to the extent that it re-awakened my interested in the movement of celestial objects and started an (expensive) avalanche.

What I hope will be the most expensive part of that avalanche hit this morning at Stockport Binocular and Telescope Centre (usual disclaimer).

I went with certain purchases in mind - but ended up buying a rather more "up-market" instrument - an 8 inch Newtonian on a motorized Dobsonian mount. Here she is after the simple assembly process for the "flat-pack" mount that was a credit to the manufacturing quality and the instructions supplied...

I had been advised throughout the "getting ready to buy" phase by my cousin, Alan, who himself is a dealer in telescopes.

This time there's no disclaimer - this is blatant advertising for a family member!

Actually, Alan has quite a lot to answer for...

As well as being part of the temptation into the world of astronomy, Alan was the guy who got me into radio all those years ago (ultimately leading to this Blog). He showed me how to make my first crystal set, he gave me the components I needed and he showed me where to buy more - either at full price from the dark and intimidating shop "Hobbs" on King Street, Luton or from the surplus bins at Surplectronics on Leagrave Road...

Lest anybody think that Alan is associated with only the finer points of my development, he was also at hand for some of the darker moments - he was Best Man at my wedding HI HI.

Thanks Alan!

"First Light" reports and impressions of the Sky-Watcher Skyliner-200P FlexTubeTM AUTO will follow - clouds permitting.

...-.- de m0xpd

Update

Well, we caught 15 minutes-worth of photons...

As the sun set this afternoon, Jupiter was the first object visible through the twilight. We could see Jupiter's weather bands and three of her moons quite distinctly, before any stars were visible to the naked eye. We just learned to drive the motor controls - to the point of turning the tracking "on" - when the clouds came and drew the curtains.

Hopefully that won't be the end for this evening.

40m Reception

2011-01-17T19:03:00.010Z

This weekend's mods to the multi-mode beacon (Blogs passim) which allowed operation on 40m have borne fruit...

I was able to see my signal on the grabber aggregators - including the excellent site maintained by Claudio, i2ndt.

Here's a reasonably clear picture of my signals at Johan, on5ex's grabber (I added a partial reflection to make my upside-down signal slightly easier to see)...

Jan, pa9qv's "Double Dutch" Grabber displays a much longer time history - so the temporal resolution isn't as fine. I've highlighted my signals (DFCW and Hell) with a red box...

Colin, g6avk, reported seeing my signals on the KnightsQRSS list - Colin said "I managed to read the inverted FSKCW here ..... It had me guessing for a while though Hi!"

Finally, Joachim, pa1gsj was kind enough to comment on the blog that he had seen my signals "the better part of the day over here in JO22da".

Joachim also made the eminently sensible suggestion that I might run the Si570 DDS oscillator at a harmonic of the desired frequency and divide down to get the three-and-a-bit Meg signal I need. That might well be the answer - I need to make a new version of the controller board (to get control lines for the band-pass filter and the yet to be constructed low-pass), so adding a divider stage after the DDS plug-in will be easy.

Thanks to Joachim for the good idea and to all reporters,

...-.- de m0xpd

Update:

Bill w4hbk has stitched together a night's worth of screens from Johan, on5ex's grabber - you can see how my signals start breaking into Belgium after breakfast at a civilised hour. Fellow WARC member Mike, g4vss, ten miles down the road, obviously has his three Weetabix a little earlier!

RIMBY

2011-01-16T15:22:00.010Z

Being accustomed to making a journey to Radio Rallies (be it a day at the seaside, risking exposure and hypothermia on the moors or just a gentle drive around the M60) it is something of a surprise when the Rally comes to me!

Today, the West Manchester club held their annual "Red Rose" Rally at a new location - the George H Carnall Sports Centre, only 3.2 miles from my back yard - how could I stay away?

The event was full of the usual suspects (including rather too many offering computers and software) and I was just beginning to regret parting with my £3 for the entry fee when I chanced upon what must be the best value "Grab Bag" of mixed components of my career - a fiver from g4vap's stand.

I had been tempted by some new DIN plugs and sockets visible on the outside of the bundle but, on getting the bag back home and sorting through the contents, I found all sorts of treasures, several of which would have been worth £5 of my money alone!

There were all sorts of goodies from passives (including dozens of electrolytics and ceramics) through multi-turn presets, switches, logic devices, RF cascode amps, relays, LEDs, sounders and earpieces, ferrites, RF chokes, 20 DIN plugs and 10 PCB DIN sockets - all of them brand spanking - an amazing haul!

The crowning glory must be the shiny new microphone holder, just visible in the centre of the picture above - whatever would I want one of those for?

Sorry - I just suffered a sudden and totally uncharacteristic bout of cynicism. I meant to say "perfect for hanging up the lollipop after a session chatting with all my good buddies, 10-4".

...-.- de m0xpd

MultiBand Beacon Progress

2011-01-15T18:05:00.008Z

After leaving undone those things which I ought to have done (beacon-wise) for too long, I finally sat down and did some PIC programming today...

I am now the proud father of another option on my menu system, which allows me to change band!

Not only does the new code allow me to display things like the image above - it actually changes the DDS oscillator too - but that's where things started to go bad...

My beacon signal generator uses a VXO system in which a 3.579MHz color burst crystal is pulled to generate the required frequency shifts. To run on 30m, my local oscillator signal from the DDS system is six-and-a-bit MegaHertz - no problem. However, to run down on 40m I would need a signal at 3.4...MHz - WHICH IS OUTSIDE THE RANGE which can be generated by the Si570.

I needed to take an alternative approach...

Fortunately the 7MHz signals can be generated by mixing my 3.5MHz signal with either another three-and-a-bit Meg signal OR a ten-and-a-bit Meg signal - so that's what I did!

Obviously, this results in an unfortunate "inversion" of the signal, such that my DFCW and Hellschreiber signals are seen "upside down" in ordinary QRSS grabbers. Here's a local Argo capture with a reflection to make matters (hopefully) clearer...

In essence, I'm now generating a lower sideband signal, rather than the original USB - I guess the answer is to flip my frequency modulations in the VXO upside down to right the wrong - that will have to wait for a while longer!

Also, I've not had a chance to get the WSPR emissions sorted on 40m as yet (they also are "upside down" and out of band). For the moment, signal reports for DFCW and S/MT Hell on 40m gratefully received!

...-.- de m0xpd

In with the new...

2011-01-01T15:32:00.017Z

Well, despite the fun of playing with new pieces of kit, I'm afraid last year's (i.e. 2010's) Winter Sports was something of a damp squib for me...

I decided to work only with my Funster Plus rig - which constrained me to 40 metres. The nearly-new FT 817 and the HW-7 offer opportunities to work different bands, but I stuck obstinately with my homebrew-only rule. If I'm honest, I see the whole QRP philosophy as only being truly fulfilled in an h/b context. I realize that is a luxury which is only open to those who brew their own - and I don't demean those whose enjoyment is served up by commercial rigs - but that's the way I like it!

I ought to confess that other distractions, including the entirely welcome distractions of celebration with friends and family and playing with the nice effects processor which Santa (aka the XYL) gave me to run with my Fender Rhodes Piano (shown here to break the visual monotony of an otherwise text-only blog),

kept me out of the shack over much of the last week, so I didn't put in the hours required to deserve a better outcome.

I had very few genuine two-way QRP QSOs, spending most of my time in very pleasant conversations with German operators with 50+ Watts. My best true "Winter Sports" hook-up was with Guenter, dl2ny, but even that was plagued by the qsb and qrm that marred most of the rest of last year's (sounds so long ago, but it was only yesterday's) experience of our qrp mini-festival on 7 MHz for me.

Perhaps this year I'll be bold enough to venture out onto some other bands for Winter Sports - that might mean modifying the Funster Plus, accepting the rock-bound constraints of the Paraset or, perhaps, building a new rig.

Hmmmm... building a new rig... could that be the basis of a New Year's Resolution?

Health and Happiness to all readers for 2011,

...-.- de m0xpd

Winter Sports Kit

2010-12-30T14:04:00.010Z

Well, the festivities have gone into remission for a day or two and my mind has switched back to the shack - not to address the boring software task which is the next step on the path to multi-band operation for the multi-mode beacon, but to get stuck into a good honest piece of mechanical work...

I had already completed the electronic side of the touch paddle - but it needed an enclosure to make it suitably robust to use in anger. I found an old Hammond enclosure, which once contained a small switch-mode audio amplifier which recently went belly up (I'm still not sure why). The donor enclosure even had a nice PP3 battery enclosure - but I needed to make a new "front panel".

The front panel has the job of supporting the paddle "blade", which is made of a sandwich of three pieces of PCB material. It occurred to me that soldering would be a good means of mechanical as well as electrical connection - so I decided to use similar fibreglass PCB material to make the new front panel.

Here's the system, without its lid on...

and this shot from the reverse angle shows how the "blades" are mounted...

Here's the finished article (with the rather more expensive "Bencher" paddle lurking ironically in the background)...

The new touch paddle partners nicely with my Funster Plus rig, to make the "Winter Sports" package seen below...

Also visible at the left of the lashed-together rig is a new, experimental CW filter I've been working on - more details to follow.

I enjoyed my first QSO with the new, boxed touch sensitive paddle with John, g4oyc and now have the opportunity to make a few more QRP contacts - with no moving parts!

...-.- de m0xpd

One Step Closer to MultiBand

2010-12-24T15:11:00.018Z

Today, making the best of a day off from the usual pattern of Fridays, I took another small step on the path to multi-band operation for the multi-mode beacon (Blogs passim). I had completed and tested the new bandpass filter (populated for 30 and 40m operation, with one as yet undedicated channel). Now it was time to install the new element in the box...

As the cold spell continues, work in my unheated workshop remains a non-starter. Accordingly, I had to drill all the new holes in the aluminium enclosure using a hand-held drill in the shack. That was going to be easy enough - but the bigger problem was with the marking out that preceded the actual drilling (all the measuring / marking kit is in the workshop and measuring, marking and centre-punching whilst balancing an object on your knee is hardly ideal). Fortunately, I had an idea...

Now - I'm sure this is "old hat" - but it had never occurred to me before. I could make full-size templates for all the boards (the new bandpass and the controller, which needed to be moved to accommodate the new board) in paper, using the Eagle PCB package with which the boards were designed. I printed them out and pasted them into the desired positions...

Voilà - marking out done "automatically" - drilling the holes was a breeze!

Here's the bandpass board in situ, beyond the re-located controller...

Notice that I didn't bother to remove the paper templates - they're not doing any harm (in fact, they add a layer of insulation, potentially useful should anything - like a rogue nut - roll under the board and short to the case).

I also decided to take the opportunity to tidy up the power distribution arrangements - previously I'd just soldered more and more pairs of wires onto the tags of the 2.1mm DC Socket and things were getting awkward. Nothing that a scrap of Veroboard and a few Molex connectors couldn't handle. I even had the foresight to include two spare connectors (which will power the receiver and the switching output LowPass filter when I get time)...

It is working FB on 30m (I've arranged things such that the BandPass board "defaults" to 30m on power up). Now, I've got a pretty big/boring programming job to do to get the system running on 30 and 40m - adding to the menu system, switching the new bandpass filter and controlling the DDS. Just the sort of job to fill up a few quiet hours when I need time away from the fun, food and drink of the Christmas festivities - or from "Winter Sports"!

Talking of which, I am listening to "the message of the angels" from King's as I write. The last verse of the Processional (with Cleobury's descant) sounded a bit shambolic, I must say! Things can only get better...

...-.- de m0xpd

Update:-

Well, the service has ended and it certainly did not get better!

It would be interesting to know if the BBC OB crew were the usual (and usually excellent) "Choral Evensong" team - poor microphone placement could have explained some of the apparent timing issues. Otherwise, more questions will be asked of Dr Cleobury, who himself asked an awful lot of the trebles to follow him on his uncomfortable harmonic contortions in the "Adeste Fidelis" descant.

Finally, perhaps it would be kindest quietly to draw a veil over the dubitable liturgical design (not to mention the ordinary, secular nonsense) demonstrated by singing "Born this Happy Morning" at a quarter past four in the afternoon!

WebSDR

2010-12-15T18:16:00.005Z

Finding myself away on a business trip once again, with time to twiddle my thumbs, I decided to take another look at what can be accessed via the Hotel’s internet connection.

Regular readers of these notes may recall that previously I’ve played with “simulated” radio connections through HamSphere whilst in ZL and QSONet whilst in HB.

Well, today I’m back in HB-land but, rather than playing with web-based simulations of the ether, I’m listening to the action on the CW segment of 40m – the real thing.

All this is thanks to WebSDR, which is a network of public-spirited Hams, who make available a software defined radio, a server and some special code developed by Dr Pieter-Tjerk de Boer of the University of Twente.

There are several people offering WebSDR receivers as I write, as listed on the WebSDR.org homepage and shown in this map…

The receivers cover various bands – I’ve particularly enjoyed listening to Dan, yo3ggx’s system in Bucharest, KN34bk. Here’s a partial screenshot of the waterfall display on Dan’s page, running Pieter-Tjerk’s application …

This is useful, interesting and fun. Not just a great boon to travellers away from their own shacks but worth looking at from home too!

Thanks Pieter-Tjerk & Dan.

…-.- de m0xpd

Touch Paddle

2010-12-06T06:15:00.016Z

The "warm spell" yesterday allowed me to make not only the PCB for my band-pass filter for the multi-mode beacon (Blogs passim) but also a PCB for the experimental capacitive touch paddle.

An unaccustomed bout of insomnia had me up very early this morning and I took the opportunity to get the PCB stuffed and working - here's the new PCB sat next to the original breadboarded prototype (and using the same capacitive paddle "blades")...

I couldn't resist trying the paddle on the air - so hooked it up to my Funster Plus (which has an internal keyer) and called CQ.

I didn't get any replies for a while but heard Andre, f5ukl, calling CQ and I answered him. He gave me a 559 and has offered to send an MP3 of the QSO - so I'll be able to hear the Funster Plus AND the new touch paddle from the "far side".

Many thanks, Andre.

I have to say, I'm very impressed with the touch paddle - I'll put it into an enclosure and use it in anger - it might not have the charm and feel of mechanical paddles, but it sure was cheaper than the Bencher!

...-.- de m0xpd

Band Switching Arrangements

2010-12-05T16:25:00.007Z

Having enjoyed little success with diode switching for the multi-mode beacon's band-pass filter, I've crossed over to a simple relay-based switching arrangement.

Each of the three bands in the unit under development has its input and output switched by a single-pole change over relay, as shown below...

The relays are switched by the circuit below (only one channel shown)...

I might not have used this design - but for the fact that it inherits much of its circuitry from the failed diode-switching circuit - indeed, I've actually stolen the components from the "diode" board!

The cold weather has been in remission today, such that I felt able to get out to the
PCB etch tank (which lives in what used to be the children's play house - now its just another "shed"). I made the re-designed PCB, drilled the myriad holes, populated and tested.

Here's the partially completed board...

I've populated two bands - for 40 and 30 m (these being the most popular QRSS bands at the moment). I've just got to wind and fit the toroids.

I'm going to leave the third channel unpopulated for the moment until I decide which other band to use.

The weather forecasters are suggesting it is going to get cold again - good job I got the PCB made today!

...-.- de m0xpd

Touching, Brass Monkeys and a Versatile Singer/Songwriter

2010-11-30T19:42:00.012Z

One of the things that caught my eye at this year's G-QRP Rishworth Mini-convention was a range of touch-sensitive paddles and associated keyers in the exhibition of homebrew. I'm afraid I don't know the brewer's name (but would be pleased to add my thanks here if anybody can help identify her/him).

I've got something of an affection for keys in general and have dabbled with making both straight keys and paddles (the latter just for fun) - but I've never tried electronic touch-sensitive paddles before. Having been touched by them (and vice versa) for the first time at Rishworth, I decided to make one...

I found a truly elegant design by Matthias Volkert, df4sq, in Sprat 48...

and - whilst I'm not interested in the keyer part of Matthias' beautiful, simple, efficient design (having the m0xpd PIC keyer and its Funky derivative), I decided to try the paddle section.

My version follows Matthias' words and music pretty closely, but with the addition of open collector outputs to connect to a keyer or a rig...

I knocked up a quick version on a solderless breadboard...

(eagle-eyed readers will see the power supply plug-in of a few weeks ago pressed into service)

The paddle was rough-hewn from PCB offcuts...

The whole thing worked very well indeed. I was keen to try it on air, but the bands were out of action last weekend due to a cacophany of QRM caused by something called CQ WW DX ("- . ... - / - . ... - / - . ... -" ad nauseam). [There is, of course, the possibility of shelter in the quiet haven of 30m during a storm of contesting - but that is occupied by my beacon!]

What's worse, I couldn't even go outside into the workshop to make a nicer paddle or a PCB for Matthias' circuit due to a spell of very cold weather! It would be nice to have been able to say "unseasonably cold weather" at that point - but extreme winters are becoming a habit.

Despite the frustrations of contesters, cold spells and failed attempts to build a switching bandpass filter, last weekend did have one high spot - and very high it was too...

A daughter had kindly given me tickets to see Sheffield's Versatile Singer/Songwriter in his "A Man with No More Rolls" tour at the DanceHouse...

Brilliant.

Anybody not familiar with Graham (a.k.a. John)'s work should take a look at his very acutely observed, skilfully delivered and immensely entertaining take on northern life.

...-.- de m0xpd

Multi-Band Beacon: WiP

2010-11-30T18:37:00.013Z

I spent some time at the weekend looking at "upgrading" the Multi-Mode Beacon (Blogs passim) to MultiBand operation. The internal DDS makes all the frequency control easy - but I need additional BandPass filters to suppress unwanted sidebands...

I designed a set of filters, similar to the 30m version already in the beacon, based upon the series resonator design in EMRFD (page 6.76). Here's my Spice Model of the (three) filters, configured for 40, 30 and 20m operation...

The predicted frequency responses of the filters are shown in the graph below...

OK - so we've got a set of bandpass filters - how should we select between them?

Obviously mechanical switches are out of the question (the rest of the Beacon being electronically controlled) so I looked for a more subtle approach. I thought I'd found it in Doug DeMaw, w1fb's article in QST, January 1991, page 24...

... in which Doug describes switching between parallel filters using diodes.

I designed a circuit, in which the chosen band is loaded into a (74137) latching demultiplexer, which switches the biasing voltage to the appropriate diode switch - here's the important part of my design...

I even got as far as a PCB...

The system works, but only up to signal levels of ~ 100mV. Above this, the diodes introduce significant non-linearity (which negates the whole purpose of the bandpass filters!!). Unfortunately, there's around 0.3V of output from my present 30m bandpass filter in the beacon, so this circuit isn't suitable - back to the drawing board!

OK - I guess Doug only intended the design as a Rx front end band-changing scheme but I was expecting the switches to work up to a larger fraction of the diode forward voltage drop.

Today, in a recourse to good old brute force "steam hammer to crack a nut" engineering, I've ordered up a bunch of PCB relays. I'll replace those dumb, non-linear diode switches with something a little more clunky!

...-.- de m0xpd

Best East-ward dx

2010-11-19T16:59:00.013Z

The last 24 hours have seen some pleasing dx spots of the WSPR emissions from my 30m multi-mode beacon (Blogs passim)...

As well as the familiar transatlantic hops, there is a nice spot from Steve, a45swl in Oman - 6049 km from my qth.

This is the furthest east my 6 Joule WSPR "flashes" have been spotted to date - and from the badly "out of tune" antenna system too.

Despite (what I imagine to be) the low density of receiving stations, it is nice to know that my signals are getting out to the Arabian Peninsula - thanks Steve.

...-.- de m0xpd

Breadboard PlugIn Modules

2010-11-18T18:15:00.008Z

I am - as regular visitors will have noticed - a fan of "Solderless Breadboards", which I find very useful for prototyping. Their usefulness is much extended by the addition of simple "PlugIn Modules" - hardly a novel idea, but immensely practical.

Today I made a power supply module, to save me adding the same set of components almost every time I knock up a new circuit...

It implements a simple 5V supply, taking power either from a 2.1mm DC jack (e.g. from a WallWart) or from a 2-pin "Molex" header (e.g. from a Battery) and regulating with a 78L05...

In truth, I power stuff under development from bench PSUs (current limiting is such a good idea for the accident-prone) but I still find it simpler to have local voltage regulation on the board - saves messing around with knobs and voltage adjustments!

Notice the little LED to remind me when power is present.

Here's the finished board...

The power supply joins an increasing collection of such "PlugIn" modules I've made over the years - usually to interface a connector or switch to the breadboard without the use of flying leads (which always live up to their name and fly off in my experience).

Here's some of the family...

There's an FCC68 break-out (used to connect the Microchip ICD2 to a PIC project under development on the Breadboard - although I tend to use the PICKit 2 nowadays - not least because of simplicity in connection!) and two flavours of switch - one "upright" and one in a more laid back posture.

I'm going to add some more modules - perhaps my favourite QRP linear amp (as previously seen in the Radio Times amplifier) and some other RF building blocks.

...-.- de m0xpd

OT: National Treasure to Perform at The Wedding?

2010-11-17T08:57:00.005Z

I would just like to add my own two pennies' worth to the groundswell of popular opinion expressing the hope that "England's Rose" will be invited to perform at The Wedding.

In light of the Chanteuse' last intrusion into Royal Soap Opera, this might present a (mercifully rare) opportunity to give another airing to that classic anthem "The Circle of Life".

...-.- de m0xpd

The Keys are Breeding

2010-11-13T16:25:00.016Z

Spent an hour at Rochdale and District ARS' "Traditional Radio Rally" this morning. I'm not quite sure what is "traditional" about it - save the rather loose affiliation between some of the visitors and modern standards of personal hygiene.

Couldn't resist another "Key WT 8 Amp" to accompany the one I'd restored from Rishworth a few weeks back. This one is a No 3 Mk I, dated 1940 and carrying the further identifying mark "ZA4605" (on further inspection, I notice this is also stamped on the base of the Rishworth model)...

This MkI is differentiated from the key I got at the G-QRP Convention by the use of a compression spring under the arm (the Rishworth Key has a tension spring above) and by the solid, machined "saddles", rather than the diecast excuses which had failed on my earlier purchase. The flat faces and sharp corners of the machined components are visible on the new key...

If anything, the new key feels better than the one I restored the other week (in which there is a little play in the un-restored central pivot).

Also, I got an old instrument case (which will live again in a new application). I didn't buy it for the case but rather for the goodies I harvested from it...

It is worth the money I paid for EITHER the BNC sockets OR the switches - for both and the case itself, a bargain!

...-.- de m0xpd

To Tune or Not To Tune?

2010-11-09T14:22:00.010Z

Now here's a pretty problem...

Last night inadvertently I left my multi-mode beacon (blogs passim) running into the g5rv - but with my MFJ 969 tuner in BYPASS Mode. The results were surprising - in fact, I think I have achieved significantly better dx than with the antenna "tuned".

Here's a map of spots over the past 24 hours...

The beacon is regularly spotted in North America, but this performance exceeds anything seen before - and the spot by Jay, w5olf in Colorado (not so far from my old home in WY) is the best dx (4537.4 miles) the beacon has achieved to date. This transatlantic spot and others into Florida and Maine were achieved this morning, continuing the recent trend for improved day-time dx. All this with the antenna de-tuned...

Here's the indicated SWR (as measured by sending a CW tone from the FT817 into the system - the beacon barely moves the needles of the meter) with the tuner active...

Here's the SWR with the tuner in BYPASS...

What's going on?

It appears that either i) there are losses in the tuner in "TUNED" mode that exceed the benefits of tuning or ii) the source impedance of the beacon is very different from 50 Ohms (the final stage is a low-pass filter, designed from standard methods assuming 50 Ohm operating impedance).

Perhaps you can suggest another explanation?

In the meantime, I guess I'll keep running the beacon into the UNTUNED g5rv !

...-.- de m0xpd

Frequency Hopping WSPR

2010-10-31T13:19:00.024Z

Since all WSPR transmissions are within tightly defined time windows and within a narrow frequency band, it is possible for two stations accidentally to interfere with each other by an unfortunate choice of transmit frequency. I decided that my multi-mode beacon presented an opportunity to experiment with "Frequency Hopping"; deliberately changing the transmit frequency in order that my "signal sees a different channel and a different set of interfering signals during each hop. This avoids the problem of failing communication at a particular frequency, because of a fade or a particular interferer."

I had fitted my control keypad into the beacon box...

... and successfully adapted my menu software to allow me to select manually from one of eleven different frequencies within the band, roughly 10 Hz apart, by adjusting the internal DDS. Then all I needed to do was implement "Slow Frequency Hopping" by allowing the controller automatically to increment the frequency through these steps after each 6 Joule burst of WSPR transmission.

For the early experiments I also shifted the DFCW and S/MT Hell emissions, as you will see...

Here's the (locally monitored) signals towards the end of the QSY cycle...

You can see the rising WSPR frequencies (at 11:48 and 11:58) and the "reset" back to the lowest frequency at 12:08.

In between, you can see my DFCW and Hell signal encroaching into the WSPR band (also there are local images which appear at spacings of [multiples of] 50Hz - so I guess they're mains "hum" related).

This was faithfully received by a number of stations, including Helmut, df5ff...

In the course of developing the code I made some accidental QSYs, including this in the DFCW signal received by Joachim, pa1gsj...

The refined controller software now allows me to "frequency hop" the WSPR signal, whilst maintaining a constant QRG for the QRSS emissions. I can switch the frequency hopping on and off and nudge the frequencies of the WSPR and QRSS signals up and down their respective bands independently.

I'll let you know if all this delivers any measurable benefit - benefit or not, it has certainly been fun!

...-.- de m0xpd

Daylight DX

2010-10-29T18:09:00.009+01:00

The multi-mode beacon has been across the pond several times (in all modes) - but previous dx has been achieved discretely, under cover of darkness.

However, today I've gone transatlantic to new WSPR participant Frank, vo1hp, in St John's, Newfoundland...

Frank has reported three spots of my 50mW signal during my "afternoon"; 12:00 - 18:00 local. At once, my signals are also getting down into Portugal and the "toe" of Italy. Clearly conditions are significantly better today than of late.

Perhaps that's good news for all those who will participate in this weekend's CQWW event on 'SSB' (whatever that is).

...-.- de m0xpd

Refurbishing a "Key WT 8 Amp No II"

2010-10-24T16:12:00.022+01:00

Had a great day yesterday at the G-QRP club's Rishworth Convention.

I was lucky to be able to chat with Roy, w7el, and thank him for his excellent "Otpimized Transceiver" design, which has inspired - more or less directly - several of my homebrew efforts, including the VFO and Rx for the Funster Plus and the beacon receiver. Introducing Roy (who turns out to be a first-rate presenter), George g3rjv mentioned the Optimized Transceiver, rightly describing it as a "Classic".

I was also pleased to meet up again with another Roy, gm4vki, who was displaying his Russian Cold war era R354 "spy" transceiver. I was first to answer Roy's CQ after he'd got the R354 running earlier this month and I was using my replica Paraset - much joking about "spy to spy contacts" and ending the cold war!

Amidst all the other junk I collected to feed my kleptomania, I was pleased to find a 1941 "8 Amp" straight key going for a song (five quid actually). Fellow WARC member Jim, g3nfb, told me how he had "liberated" a similar key as a youngster - directly from a Lancaster!

I noticed that the key had a little damage - but it wasn't until I got it home that I realized the diecast yokes at either end of the key were cracked (I guess they used all the good metal on the Lancasters) ...

The bits had been put back together with superglue (which had made an insulating open circuit in the rear yoke with the result that even though the key felt nice, it didn't work as an electrical switch).

It has been a long time since I did much in the workshop (what with all the recent fun and games with the beacon) so I decided to spend some of today making some replacement parts to bring the key back to working order. I found some 1/2 inch thick alloy plate and hacked out a blank, which I squared up in my horizontal mill (itself a piece of history)...

I marked up for a couple of replacement "yokes" back-to back...

... and soon had them roughed out ...

After drilling and tapping the various holes, I filed the yokes to shape, trying to recreate something of the look of the cast originals. The result is seen below - I deliberately left the orange £5 price tag on for the camera so I can feel good about it!

Here's another view - it is mounted on a brass baseplate (which itself bears the marking "Key and Plug Assembly No 6" - no idea of the provenance of that component but it sounds "military").

I think it looks pretty authentic and - most importantly - it works again. Now perhaps I'll turn my attention to the pa0klt synth kit I got from Jan, g0bbl.

...-.- de m0xpd

Back to the G5RV

2010-10-18T18:39:00.001+01:00

Last weekend I knew I wasn't going to be using the g5rv, so I decided to try my multi-mode beacon into that antenna once again.

Regular readers will recall that I have installed a dedicated antenna for 30m beacon work (with the intention of leaving the main station antenna free for other uses). The dedicated beacon antenna is known to be something of a "compromise" - it is just a pair of Moonraker 30m whips mounted on one of their "dipole centres", to make what I have named the "runt dipole".

When I first set up the system, I had results slightly poorer to those achieved with the g5rv, but I was ready to accept the poorer performance in return for the ability to run other modes at the same time as the beacon (which runs 24/7).

I switched over to the g5rv on Friday 15th and was immediately rewarded by an email from David, ea1faq, telling me that he'd got a nice grab of my S/MT Hell signal...

As you see, David had captured my DFCW signal as well - in fact David has done great service to me, having also spotted the beacon's WSPR signals many times in the past. That's 3/3 modes - thanks David!

I left the beacon running to allow me to average over a full 72 hours of performance on WSPR and very soon it became clear that the performance with the g5rv was much better than before. Here's a comparison of the original averaged report rates on the g5rv (blue), the averages on the new "runt dipole" (red) and those on the recent return to the g5rv (green)...

For those of you who have not seen these averages before, I am counting the number of reports of each five-and-a-bit Joule "flash" of WSPR signal, which occur every ten minutes and averaging over several days of data. For the original g5rv data, the average runs over 13 (consecutive) days. For the new "runt dipole", the averaging extends over nearly five weeks (hence the smoother curve), whilst for the re-visit to the g5rv, there's just last weekend's three days of data averaged together.

In all cases, the beacon is running 50mW of power.

In spite of the risk of comparing Apples with Pears, I think it is fair to say that the performance with the g5rv is significantly better than it was before - and significantly better than with the "runt dipole".

As if the performance figures with WSPR weren't enough to be happy with, my email inbox this morning contained another pleasant surprise...

Colin, g6avk had posted on the KnightsQRSS list a description of an unusually strong signal...

Well this surprised me this evening, whilst working in shack #2 this huge S3-5 signal appeared on 30m, on checking my grabber in shack #1 it turns out to be Paul M0XPD.

The subject of Colin's post says it all: "Freak condx or QRO :)". I assured him that it is still the same old QRPp 50 mWatts and that the only change is the antenna. However, the great WSPR performance (compared to that achieved six weeks ago) certainly suggests that propagation has improved markedly too.

Thanks to all those who operate receiving stations for WSPR and QRSS - I'll get round to doing some Rx myself some day.

...-.- de m0xpd

Bad Case of the DTs

2010-10-10T06:15:00.004+01:00

Fear not, dear reader - I haven't given up the sauce. I am not in withdrawal, suffering severe autonomic instability. I refer not to Delirium Tremens, but to time differences, dt. Specifically to the "DT" data column in the WSPR GUI...

Everything was going FB with the multi-mode beacon and its new internal DDS until Thursday, when I started to notice large (and apparently random) timing errors. You can see the fall-off in performance on Thursday in this plot of the number of spots in each 24 hour period over the past two weeks...

The time errors "DT" were accumulating at an alarming rate, suggesting an impossible variation in my beacon controller's fundamental clock frequency.

Eventually I discovered it was caused by some kind of interaction between the new Controller board and DDS and the main VXO system. The interaction was either conducted through ground, power lines or interface lines or through radiation from clocks, RF sources etc... Whatever the cause, simply un-plugging the controller (and reverting to the SDR Kits USB synth) has cleared up the jitters for the moment.

All of which gives me time to address the issue of providing an interface between me and the Beacon Controller system. Remember - I needed some switches...

I had so much fun with building the DDS board in surface mount technology that I decided to stick in the nano scale and got some tiny tactile momentary action switches from Farnell (seen here against a PIC 16F873 for scale)...

Here's the schematic of my keypad...

...a conventional layout in which columns of switches are sequentially pulled low by pull-down transistors (in this case MMBT3904s - the surface-mount version of my beloved 2n3904) and read in "rows". I arranged two columns of three switches - four "arrow" keys to navigate up/down, left/right and two (as yet) un-designated switches.

The "arrow" keys are seen at the right-hand-side of the finished "Keypad" board...

That was the easy bit - now to code the PIC!

The actual software interface to the keypad is simple enough - the only real issue being the optimisation of the delays and rules for switch de-bouncing. I tested for two consecutive valid "reads" of the same key, separated by a small delay and then imposed another delay before looking for another key push. However, reading the state of a key and getting that state to do something useful are two very different things - especially in assembly language!

I have implemented a menu structure, in which the left/right keys are used to navigate from the "standard" operating configuration ("Menu 0") to a umber of other menu "pages". Each page has a (programmable) number of options, which are selected using the up/down keys (including a Boolean "On/Off" option if required)...

Here's a (bad) photo of the display telling me where I am...

The banner "Menu 1" is just a text string, such that I easily can replace it with something more descriptive...

Whilst I haven't yet finally decided what to do with the controller, the outline plans are for...

Menu	Name	# Options	Function
1	dF	~10	nudge freq up/down to avoid QRM
2	Band	4	Change Band (30m, 40m, ??)
3	Frequency Hop	On/Off	cycle through a defined band

That's all development effort (i.e. tedious coding) for the future - for now I must return to the job of fixing the timing errors inside the beacon. Some screening and some (more) power supply de-coupling will be the first ports of call.

...-.- de m0xpd

Post Script

Once again Google kindly has arranged for the image upload feature of Blogger not to work early on a Sunday morning when I want to post. He might not be watching me, but Big Brother is certainly deciding when I'm allowed to make my diary entries.

I did "try again in 30 seconds" - several times but to no avail. However, as you see, it worked fine when I came back at 09:15 local, by which time the servers had woken from their slumbers (but I still can't change the colour of the "Post Script" heading - What You See Is NOT What You Get).

Beacon DDS

2010-10-03T11:58:00.000+01:00

I'm pleased to be able to report that the multi-mode beacon (Blogs passim) now has its own h/b Direct Digital Synthesizer...

As regular readers will recall, the m0xpd beacon has been using the excellent SDR Kits USB synthesizer. Whilst being a perfect solution in a PC-based system, the USB Synth is not so handy in the context of microcontrollers (which don't have USB as a matter of course) or stand-alone beacons. An internal DDS would give me freedom from the PC on start-up (previously, I'd had to set up the synth via USB) and flexibility to make the beacon multi-band and frequency-agile.

I decided to use the same Silicon Labs Si570 device featured in the SDR Kits synth (not least because Jan, g0bbl, sells them). However, in making that decision, I was forced to accept a couple of challenges...

the Si570 is 3.3V powered and so would need level conversion to interface to my 5V PIC environment
the Si570 is a surface mount device - so I would have to enter the scary world of MICRO electronics - no mean feat for somebody who has worn spectacles since age five and has an intention tremor (at least I had an intention tremor - but that has been much improved since my physician prescribed Beta Blockers for migraine prophylaxis)!

The first challenge was easily solved using a simple circuit I found on the 'net (as used in a nice little level converter module available from Sparkfun)...

I could only get hold of the MOSFETs in surface mount packages, so that really sealed the deal - I HAD to adopt surface mount technology! Anyway - here's the proof that the level converter circuit works as intended...

and here's my completed schematic (with level conversion on the data and clock lines)...

Although I'd never played with surface mount before (in an h/b context) my trusty Eagle PCB package could handle it effortlessly and a PCB design was soon produced...

(In truth this was the second design - I had not bothered to read the data sheet for the LP2950 LDO regulator I chose to generate the 3V3 line and so missed out the loading capacitor which stabilises it!)

Here's the finished board in the development context plugged into a breadboard...

Once I'd confirmed operation of the hardware I could look at the software required to make the Si570 do its stuff...

The synth module was designed to interface to my controller board over the Si570's two-wire I²C interface. I was delighted to find that Andrew, g40ep had trodden this path before me and has generously posted a mine of useful information and software on the 'net. It is (as Sir Isaac understood) good to be able to hitch a ride on the shoulders of giants - thanks Andrew! Follow this link to see Andrew's Si570 resources.

I borrowed heavily from some of Andrew's I²C routines (simplified somewhat by my bi-directional level converter on the serial data line). I decided, however, to take a simple brute-force approach to setting the Si570's frequency to get things running quickly...

I had noticed that one of the PC utilities provided with the original SDR Kits USB synth produced register contents associated with any frequency setting...

Accordingly, I simply programmed my new PIC 16F873 in the controller board (the original 16F872 has been replaced, as I wanted to duplicate the system on the external breadboard and the junk box only had one 16F872!)...

to send the "brute force" register contents to the waiting Si570 and - Hey presto - the beacon is up and running with its own internal DDS...

Michael, dl5ocd, was first to spot the beacon in its new configuration.

Now I'm ready to extend the operating flexibility of the system - but first I have to arrange some switches to tell the beacon what I want it to do!

This has been great fun (so much so that I've ordered a complete set of 1206 resistors and a set of caps) and I've learned a lot along the way.

...-.- de m0xpd

Beacon developments

2010-09-26T17:49:00.000+01:00

The next step with the multi-mode beacon is a bespoke synth to replace the SDR Kits USB synth currently used.

I've decided to use the same Si570 chip used in the SDR Kits synth - which introduces the exciting prospect of homebrewing with surface mount devices!

Rather than make a whole board for the synth (thereby committing an expensive Si570 chip to single use), I've decided to make a small surface mount "carrier" for the Si570 and associated circuitry (3.3 V supply and level converters for the control signals) and arrange for this to plug into a larger "control board" using good old through-hole technology. This control board will drive the Si570, provide a "user interface" through an LCD display and some push-buttons and generally supervise operation of the entire beacon - hence the name "control".

Here's the board, mounted in the big box...

The main device is a PIC 16F872A - chosen because it has plenty of I/O pins and it was in the "junk box". The three holes near the crystal aren't a mistake - they're for a trimmer cap if I ever decide that this PIC needs to keep accurate track of the time. The Si570 carrier board will plug into the two four-pin sockets North-East of the PIC. You can also see the usual colourful parallel interface to the LCD, a multi-pin header to link to pushbuttons (etc), an in-circuit programming interface (I know I'm going to be re-programming this PIC!!) and a three-wire interface to the hi-rise controller board, through which the operating mode of the beacon can now be tracked.

Here's the display, proudly announcing the operating mode at the time of taking the photo...

I have actually made the carrier PCB - but not started populating it yet. Today is the morning after a particularly heavy "night before" and I didn't feel messing with microscopic surface mount devices would work as "hair of the dog" !

...-.- de m0xpd

WSPR Stats with the "Runt Dipole"

2010-09-19T11:48:00.000+01:00

I have now collected a week's worth of WSPR reception reports from the multi-mode beacon running with the new dedicated antenna, which I've named the "runt dipole".

The first night's operation suggested that the new antenna compares reasonably with the g5rv - but the week-long averages reveal a more complicated story...

Here's the average of the reception rates for the g5rv (in blue, as previously reported) and the new antenna (in red):

The performance of both antennae throughout the "Quiet Nights" average out similarly and the new antenna is pretty close to matching the rate at which emissions from the g5rv are spotted during the morning. However, the average performance with the new antenna is poorer in the evening - the spot rate is less than half that achieved with the g5rv.

The new "runt dipole" is - as its name suggests - nowhere near as effective a radiator as the g5rv, yet the overall reception rates are really quite reasonable. So what's going on?

I believe the answer lies in the directionality of the new antenna.

I explained previously that the g5rv lies approximately N-S, whereas the new antenna is close to NW-SE. I predicted that this would direct my beacon signals to a different set of potential receiving stations and this prediction is borne out by the reception reports.

If I look at the azimuth angle in all the reception reports and count them in angular
bins "around the compass" - effectively making a probability density estimate of reception rate against angle - the following results...

The very great majority of the reception reports associated with the g5rv were at an angle of 110 - 120 degrees from my QTH, taking the signal to Germany, Switzerland, Italy, etc. This is seen by the clear "lobe" in the g5rv data, above left.

In contrast, the reception reports associated with the new "runt dipole" are seen in the figure above right to be more uniformly distributed around the compass - the NW-SE orientation of the antenna gives better performance North and South, taking me to Spain (lots of spots from Javier, ea1jl), Iceland (the little spike pointing broadly NW shows how I reached Halldor, tf3hz) and into Scandinavia (solid, reliable propagation to Jon Ove, la3jj) as well as continuing propagation into Germany etc..

The ESE lobe in the g5rv data broadly pointing towards Germany is preserved in the "runt dipole" data - but I believe this is a reflection of the higher receiving station density (and, hence the increased probability of reception) in this direction, rather than anything to do with the radiation patterns of either antenna. This irregular location of the receiving stations is, of course, one of the charms(/frustrations) of WSPR!

All-in-all, I consider the "runt dipole" to be a success. It isn't up to the absolute performance of the g5rv (naturally), but its different orientation makes possible a satisfying range of beacon spots and succeeds in the original aim of freeing up the main station antenna. Not bad for a pair of inexpensive mono-band whips!

I'll be leaving the beacon running 24/7 and posting more stats/observations when there is something interesting to say.

...-.- de m0xpd

HELL Jumps the Ditch

2010-09-17T19:00:00.000+01:00

Although the WSPR emissions of my multi-mode beacon have been steadily reported (more statistics to follow at the end of a full week's observation), the other modes have disappointed me since switching to the new dedicated "runt dipole" antenna.

I had been used to being spotted on the European QRSS grabbers back in the days when I used the g5rv - but not a sign since installing the new beacon antenna. However, all that changed today...

In a message on the KnightsQRSS mailing list, Vernon, VE1VDM asked if he was seeing things amidst the noise... sure enough, it was my S/MT Hell signal, weakly copied in Nova Scotia...

I've put the red box around the signal to make it clearer - you can see the "xpd" clearly enough (especially if you know what you're looking for ).

Vernon's "BIG EARS grabber" is 2706 miles from my QTH...

making this the best dx (2706 miles for 50mW) I've enjoyed with the HELL mode.

Many thanks to Vernon for running the grabber and for providing the report.

...-.- de m0xpd

Joe spots my Beacon-in-a-Box

2010-09-13T18:27:00.000+01:00

Having enjoyed building the new "runt dipole" antenna for the multi-mode beacon, I decided it was finally time to put the whole shooting match into a box...

The box is a cheap aluminium offering from Maplin (code KR55) which is reasonably new to Maplin's range. I marked out the front panel to take a reset push-button and an LCD display (which I picked up from Hua Qiang Bei Lu Technology Market) as I intend to add a self-contained DDS to replace the USB Synth - eventually. You'll see that the box has plenty of space for the DDS, my receiver and some other goodies (don't tell anyone, but I'm thinking of going multi-band).

The existing boards were just positioned in (what seemed to be) a rational layout (with the output LPF currently a temporary fixture)...

On the back you can see (left to right) RF out, RS232, USB (for the Synth), and DC in...

Note that I haven't yet peeled off the protective white film - I've still got some more metalwork to do (fitting controls for the DDS etc - once I decide what controls to fit HI HI).

I fired up the beacon again and left it running overnight - I was delighted that the first transatlantic hop with the new antenna (not to mention from the new box) should be spotted by none other than the great Joe Taylor, K1JT, himself...

WSPR returning to its creator!

Although the WSPR reports have been pleasing, I've been disappointed so far by the performance of the other modes.

I'm leaving the beacon running pretty much continuously for a while to gather some more WSPR stats.

...-.- de m0xpd

New Beacon Antenna

2010-09-12T11:10:00.000+01:00

Being close to Bletchley Park last week also placed me close to Moonraker's shop - I couldn't resist popping in for a poke about.

Despite warnings to the contrary, I was tempted to buy a couple of monoband whips and a centre piece to make up a (very) short "dipole". I had already been persuaded of the usefulness of short base-loaded whips in using my Walkabout antenna and so - given that they aren't exactly expensive - I got a brace of 30m antennas.

I've been wanting a permanent antenna solution for the multi-mode 30m beacon (being frustrated by giving over the station g5rv to beacon duties). Although I haven't yet finished my experiments with loops, I decided to give the whips a try...

I used to have a 2m colinear mounted on the end of my garage, but I wasn't getting much value out of it (I only occasionally fire out an APRS signal on VHF and I can't match the erudition of those using the CB proxy which 2m NBFM seems to amount to). So - I pulled down the colinear and put up my new "runt" dipole in its place.

I left the beacon running overnight with the usual 50mW output and here's the performance, plotted as spot count in each contiguous 10-minute interval, (shown in red) against the "average" performance experienced over recent weeks (in blue)...

Bottom line is - whatever the shortcomings of the new antenna and its radiating environment (low down, close to my garage and extension roofs), the performance isn't really significantly short of the average achieved with the g5rv! I did miss my occasional overnight dx - but this first night's data isn't exactly statistically significant.

The g5rv runs pretty much N-S, whereas the new "runt" dipole runs NW-SE. This seems to have given me slightly better projection into Scandinavia than I was achieving with the g5rv (actually, I was getting signals up into arctic Norway when the g5rv's centre connections were faulty - obviously this was result of the inevitable disruption to the radiation pattern, accompanying the observed disruption to the load presented to the transmitter)...

Clearly, I need to collect more data before jumping to any conclusions but - for now at least - I am enjoying the luxury of a dedicated 30m antenna for the beacon, leaving my main antenna free for whatever else takes my fancy !

...-.- de m0xpd

A Grand Day Out

2010-09-06T11:14:00.000+01:00

Having recently finished reading B Jack Copeland et al's book "Colossus: The secrets of Bletchley Park's code-breaking computers" (which get's a very enthusiastic "thumbs up" from me) you will imagine my delight to have found myself within striking distance of Bletchley Park today.

The XYL and I set off on the forty minute drive not knowing we would arrive to find a special "Churchill Weekend" event at BP, in which many veterans were gathered for the unveiling of a new monument (a stone in front of the mansion, "representing" the stone on which Sir Winston stood as he addressed those serving at Station X). Here are some of the dignitaries and "top brass" gathering outside the mansion...

The Rolls Royce is the particular car which Winston used to commute from London to Chartwell.

We started our visit by paying homage to the "Bombe", Alan Turing's development of the mechanical device first built by Polish Codebreakers to break Enigma keys...

Then we visited Tony Sale's rebuild of the Colossus computer. Looking back at the experience, I realize that I'd strolled casually past some nice radio gear (including an array of AR88's like mine), parts of "Heath Robinson" (Colossus' electro-mechanical predecessor) and the duplicate "Tunny" machine, (on which the actual de-cyphering of Tunny/Lorenz traffic could be performed once Colossus had worked its magic) almost without pause. Before I knew it I was there, inside an un-assuming building, staring at the Holy of Holies.

Make no mistake - this is IT. This is the Garden of Eden. This is the singular point at the origin of the modern world. Yet I'd drifted up to it without all the preparation that should be made before gazing on the face of Glory...

Slowly, it all began to sink in. I attuned to the heartbeat of the beast as it reset counters between each scan of the message on the "near" drive of the "bedstead". I started to see the elements that I'd only read of in "Scripture" - the optical reader (which read the bits from each of the five channels or "impulses" as they were then named), the span indicators (which allowed cryptanalysts to start and stop computation at fixed points within a message), the switches for encoding "ordinary" Boolean operations (this is a rebuild of a Colossus II) and the teletype machine which recorded results.

Here it was - here I was. Standing in front of the work of man (principally the work of one man - Thomas H Flowers) which encapsulated and transcended the work of all humankind. Sacrament in reverse.

After conversation with one of the high priests (/technicians) who serve at this altar, I was given a gift I will treasure - a piece of tape that had been through the machine...

I read the first few characters (from the"torn" X at the left hand extreme) as

'X/(lf)/OUWGNZQLI(lf)/N(cr)NSZCTK/++L(sp)(lf)L...'

in which I've stayed in letter shift of the Teleprinter Alphabet and used (lf) to denote "line feed" etc. Gobbledegook!

It would have been enough to leave Bletchley at this point - but there was more to see...

In another unassuming building - "Hut 1" - is housed a collection of Diplomatic Wireless equipment of international importance. It is curated (and part-owned) by David Wright, g3zpa, who showed me around. I was particularly keen to see the original Parasets - there is both a metal boxed version and the wooden model, seen here...

David made some gracious comments about the photographs of my replica Paraset. He also allowed me to take some key dimensions of the Whaddon MkIII transmitter - perhaps that will be a future project!

David reminded me that the book "Secret Wireless War", by Geoffrey Pidgeon was available at the shop and I was pleased to get a copy.

To end a great visit, we were treated to a fly-past from Lancaster PA474 from the Battle of Britain Memorial Flight, which made three passes over BP...

All the ingredients of "A Grand Day Out".

...-.- de m0xpd

13 Days of WSPR Spot Stats

2010-09-04T09:07:00.000+01:00

The multi-mode beacon has now been running for nearly two weeks (during much of which I've been away on business - I write from HB-land).

Here's the overnight spots for the period...

You can see that my earlier thesis of "quiet nights" holds pretty well for weekdays - but there was some activity through the nights last weekend.

The pattern is perhaps clearer by averaging across the daily records, the result of which is seen here...

I'm still travelling throughout next week - but there's nobody at home to pull the power on my remote command, so the beacon is now QRT for a while.

...-.- de m0xpd