New Licences and the 60m Minefield

UK amateurs have been receiving new licences over the past few weeks from our dear licencing authority, OFCOM.

The licences arrived (here at m0xpd, at least) by email and are pdf files, named by the licence number - having exactly the same name as the licence they are to replace (making it impossible to keep them in the same folder for comparison purposes).

I didn't surrender my foundation and intermediate licence (which arrived a few days ago) and my full licence arrived last, at which point I finally bothered to take a look and see what all the fuss was about.

Truth is, there is very little difference of any interest to me - in fact, the only matter of any real interest is the change in handling the 60m band from a Notice of Variation ('NoV') to a standard clause in the new full license.

Here's the new detailed description of the UK full licencee's rights on 60m...

I must confess, it caught me rather by surprise - particularly as I'd never looked into 60m before much less actually operated on 60m (the obstacle represented by the whole tedious process of applying for the NoV saw to that).

My surprise was  associated with the complexity of the description of the band above - as compared to the simplicity of (for example) the adjacent 80 and 40m bands. This surprise was piqued when I noted the notes...

You need to tread very carefully in this minefield of band limits to "ensure radiation does not take place outside the specified frequencies". Further, with the frequency bands presented in the format used in the license, I could not easily see exactly where a 6kHz band was available - if at all - to those poor fools who might like to use DSB. So I figured it out...

After going to the trouble of figuring it out, I found almost exactly the same information on line, which is always rather deflating. So here's an alternative way of visualizing those parts of the 60m band on which we are safe to tread...

As you see, there are 5 (of 11)  places on 60m where a DSB enthusiast could hang their hat. Otherwise, it is all SSB and narrowband modes.

What I had completely failed to understand before my new license arrived (and, hence, what surprised me) is that 60m is effectively channelized - it grew out of an intention that the band would be operated with a set of discrete (USB) dial frequencies for voice and the rest of the spectrum in between these points is pretty much a minefield (little wonder the "military" gets so much mention in this context in our new license).

It was in this state of ignorant bliss that I had provided the Kanga VFO with a continuous sweep between 5.2585 and 5.4065 MHz...

What am I going to do about it?

Nothing!

Except from write this blog post. The VFO is just a demonstration of what's possible with the technology building blocks rather than anything more. It could be elaborated to switch through the channelized USB frequencies on 60m, but let's just say that task is nowhere near the top of my to do list.

Neither, in all honesty, is exercising my new-found rights to operate on the 5 MHz band.

...-.- de m0xpd

Suddenly Direct Conversion

As mentioned recently, there has been a resurgence of interest in the receiver section of the Occam's Microcontroller system - which itself was inspired by George, g3rjv's Sudden...

This has inspired Dennis g6ybc and I to dust off my prototype PCB and make some new ones, which I populated yesterday.

The PCB is in the format of an Arduino Shield - but it will run happily enough as a stand-alone receiver - which was the mode in which I first tested it yesterday.

The oscillator signal was furnished by the Kanga VFO system, and I listened on 20m.

Today I listened to the fun and games leading up to Guenter, dj2xb's valiant attempts to read the news on 7.127 MHz. To do that, I mounted the receiver, as intended, atop a stack formed of an Arduino, an Si5351 shield and the new receiver...

The eagle-eyed may notice that there are a few components missing from the PCB in the picture of the shield - these missing components are explained by the facts that i) they're not required to get the receiver running and ii) I'm planning to do some optimisation in these areas.

The key areas are highlighted below...

Receiver  muting is a little noisy in the prototype and uses a transistor which isn't so easy to source. The CW sidetone in the Occam's transceivers is a squarewave generated by the Arduino - I would like to check my first attempts to filter it. Finally, the Occam projects were conceived back in the AD9850 DDS era, when the RF oscillator was (nearly) a sinusoid. Whilst both the Tx and Rx shield run FB on the squarewave signals from the Si5351 shield, I'd like to look at optimising level and (potentially) some filtering of the oscillator signal to the 602 on the Rx shield.

The stack is also seen here...

The Si5351 shield is actually a pre-production prototype, the PCB for which also arrived this week "hot off the press". It has a jumper to select input logic level (3v3 or 5v) and a jumper to power up the amplifiers (or leave them powered down to save power or power them from an external voltage source)...

It also features (in this clumsy build, at least) toroids which are way TOO BIG! Yesterday morning I was listening to a nice BBC radio 4 documentary, in which some of the technology predictions of Douglas Adams were being put to the test as background entertainment whilst I was stuffing the Si5351 board and - being distracted by this interesting material - I didn't notice the "terrible miscalculation of scale".

The little DC receiver sounds fine - apparently g6ybc has his receiver running too.

This morning I was happily listening to able to hear dj2xb reading the RSGB news on 7.127 until dk5dr started chatting to g0jmz on 7.130 and I remembered just what "fun" wide-open direct conversion receivers are!

...-.- de m0xpd

Parallel IF for the Vero BITX

Last week's new home for the plug-in modules had a Parallel IF path - but needed some more work...

Specifically, I was actually only running the ordinary Si5351 code - which doesn't support the switching IF frequencies required for the Parallel IF method.

Also, whilst I had two filter modules (as you saw in last week's photos), the 12 MHz unit had only been thrown together without any serious testing.

The technique for direct measurement of receiving response actually makes a nice framework for developing IF filters - because it places them in their intended operating environment (unlike my earlier simplified attempts).

Here's the measured response of the 12 MHz unit as it was first thrown together...

As you see, it is rather wide - in fact it sounded fine (if rather muffled) on voice.

Taking the plug-in rig as an experimental platform, I started messing with an alternative 12 MHz filter on a solderless breadboard (what else!)...

and I soon found a better (i.e. narrower) overall measured receiving response for the entire rig in "CW" mode...

Remember - this isn't just what the IF filter does - it is the response of the whole rig, warts 'n all.

I changed the capacitors on the plug-in module (but kept the crystals the same) and got a better response than the original - but not as good as the one above...

Good enough for who it's for.

A quick change to the software, to incorporate all the Parallel IF bells 'n whistles (especially the on-line alignment facility, so I could optimise the BFO settings for the new filter) and I was done.

Here's the current measured response in SSB mode..

and in CW mode...

Switching between the two is pretty dramatic - especially on a crowded band.

Also, this (today) is the first time I've heard the Parallel IF method running from the Si5351 (Pete, n6qw, has been running it on the left coast).

My original Parallel Rig is still using a pair of AD9850 DDS Modules and they are never PERFECTLY in tune with each other. So, switching from SSB to CW mode whilst listening to CW can cause a tiny pitch change in the incoming CW, which I can sometimes hear.

It is inaudible on voice, but sometimes audible - particularly to those with any musical sensibility - on CW. Some days it is imperceptible. Other days (at different temperatures), it is there.

On the Si5351, where both the clocks are derived ultimately from a single oscillator, there is no "tuning" issue. Joy!

The strip of stripboard really is a nice demo of the Parallel IF method.

It is also a nice demonstration of why you shouldn't mount a computer right next to the front-end of a receiver. It works well and is entirely usable - but you get a little audible tone whenever a control is operated.

Perhaps I will try to persuade audiences that it is an intended feature (which took me ages to code)!!

...-.- de m0xpd

Pluggin' Away

More development of the Plug-In BITX Module concept...

Having taken delivery of a bumper bundle of 40 pin 0.1 inch female header connectors from Banggood for the price of a pint of beer (including shipping a third of the way around the world)...

I was in a position to move my plugin BITX from its premium plot on a solderless breadboard to a permanent and inexpensive brownfield location...

My three K and H AD-13 breadboards are great for the development of pretty sophisticated projects. But recently, they have become the homes of almost permanent installations, blocking them for their intended function of development canvasses.

Until yesterday, there's been the aforementioned BITX, the Arduino SDR system and the Digital Tube Screamer squandering premium space on my large breadboards...

Some correspondents have asked about these breadboards - including questions about suppliers. I took a look a few days ago and it seems that my original supplier (Maplin here in the UK) no longer stocks this model - so even I can't replace these  precious resources. Freeing up the land for more development is important - but it wasn't my only motive.

I've a couple of talks coming up this month at radio clubs in the North West of England, where I'll be mentioning the Parallel IF method, and having a convenient, robust demo system will be an advantage. Plus, I wanted a system I could put into my luggage for the big trip to Ohio for FDIM.

Here's an aerial view of the (nearly) finished, but fully working unit...

Power comes in at the top, RF from the antenna in at the left hand side of the picture and AF output to speaker or 'phones from the right. I built a tuning control, push-buttons and space for the display onto the board - to form a complete user interface. The system is self-contained apart from power supply, speaker and antenna.

The elements of the system are emphasised in the annotated image below...

Most important is the pair of parallel IF plug-in crystal filters seen close to the middle of the system. Otherwise, there's a straight-through signal path from left to right (for receive).

As I write, I've been listening to the build-up to the RSGB news on 40m, with the unequal struggle between people exciting the ether at 7150 kHz with UK legal limit and "QSY Old Man" and others from across the seas with a more cavalier approach. Highly entertaining!

To close, a little story for St David's Day...

I was inspired by Mike Richards, g4wnc's writing in the current number of RadCom - so I splashed out on a new Raspberry Pi 2 Model B...

As you see, I got my Pi (and a little 8GB SD card with an OS already on it) from the nice folks at The Pi Hut (usual disclaimer).

I'm no stranger to Raspberries - here's the newcomer sat next to the slower original model B, which it is now upstaging...

Following g4wnc's suggestion, I thought I'd try the Pi with FLDIGI - so, at risk of poisoning the feckless, I set about ordering a Daffodil USB Sound card. Those of you who have been near Google today will know that the Daffodil is the national flower of Wales, of which David is patron Saint...

I could have ordered a "Daff" from a certain global on-line retailer (of which I am a frequent and satisfied customer) associated with powerful women and rain forests.

Instead, I ordered from an outfit called Digital Daffodil through that equally ubiquitous on-line auction site you will have heard about. I handed over less than half the money I was asked for by the on-line retailer (postage and package included) and my Soundcard was in my grubby hands in LESS THAN 24 HOURS. That's what I call good service! No affiliation - except as satisfied customer.

The new Pi - and FLDIGI - work FB.

Let's hope Digital Daffodil's premises are nowhere near food outlets!

...-.- de m0xpd