Frequency Hopping WSPR

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

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"

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

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

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

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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

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