Sunday 26 September 2010

Beacon developments

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

Sunday 19 September 2010

WSPR Stats with the "Runt Dipole"

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

Friday 17 September 2010

HELL Jumps the Ditch

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

Monday 13 September 2010

Joe spots my Beacon-in-a-Box

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

Sunday 12 September 2010

New Beacon Antenna

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

Monday 6 September 2010

A Grand Day Out

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


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

Saturday 4 September 2010

13 Days of WSPR Spot Stats

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