Monday, 17 February 2014

Ultimate3 QRSS Beacon kit built!

At the start of the year I did some experimentation with cheap DDS modules based on the Analog Devices AD9850 connected to the Arduino board, making a rudimentary WSPR transmitter prototype.

My current licence restrictions prevent me using anything home-brew for transmitting except for commercial kits. So I ordered an Ultimate3 QRSS beacon kit from Hans Summers (G0UPL) thinking that it would be okay. I subsequently learned that any commercially available kit must satisfy IR 2028 which is all a bit vague and unclear but sadly I don't believe this particular kit does.

All was not lost, building this kit should more than satisfy one of the practical assessments of the intermediate examination, which will get me around this problem.

The Ultimate3 kit is extremely popular and so I had to wait a little for delivery and it arrived on Friday. After the last few weekends of non-radio activities I had planned to get my antennas backup and do some proper operating. Like many people I had been forced to take everything down due to the barrage of storms and high winds the UK has been experiencing recently.

A tidy workbench

Saturday saw no let up in the wind, so I decided to spend a few hours building the kit instead.

The instructions were extremely clear and straight forward and soon had it built up, though it is high time I invested in new soldering station. I have a basic Antex 25W iron. I cannot remember exactly when I brought it but it is well over 10 years ago.  It was more than adequate to build this kit and for soldering connectors but I could do with something adjustable and more comfortable.

Taking shape
The only issue I had was winding the first toroid, 25 turns later I realised I had wound it the wrong way round so the leads didn't line up with the holes in the PCB. I could have made it fit but nope I will do it properly so I unwound it and did it again.

I also made the mistake of not scraping the enamel off the toroid wire and tried the heat it and bubble it off method, except I think my iron just isn't hot enough so ended up using a piece of wire wool to remove the enamel.

Lessons learned I soon had the other three toroids correctly wound and wire prepared for the low-pass filter board.
Close up of the LPF
   A final visual check and powered it up and it worked first time!

All built
It works!

Setting it up
Full of confidence I grabbed my trusty GPS module which has been pressed into service on a few Arduino projects including the HAB project. Quickly soldered some connecting wires and powered everything up.. all was well or so it seemed when the display suddenly went blank, backlight was on, just no characters.

Pressing the button I occasionally got some random characters and a flashing cursor! I de-soldered the GPS and still nothing. I suspected the display was faulty but trying it on the HAB prototype board confirmed it was okay. I checked the display connector continuity and everything appeared okay.

Out with the oscilloscope I started probing, everything checked out. Crystal was oscillating and data pulses on the display control lines. Then I checked the supply pin on the display and it was only reading 4.1V, this under-voltage would explain the odd display behaviour.

PSU output was 5V, micro-controller was 5V, DDS module had 5V. All very puzzling till I removed the DDS module and spotted a discoloured track on the PCB, touching it with a screwdriver and the lacquer fell away revealing a tell tale scorch mark, somehow I had made a nice resistor!

Burnt track to right of micro-controller
A quick wire link soldered in place and everything was back to normal.

What caused it? Checking the de-soldered GPS connecting wire I spotted a stray single strand of wire on the ground wire. I suspect this must have shorted to the adjacent 5V line and since I was using a nice beefy ex-PC PSU as a bench supply it had popped the track without the hint of a flicker. The GPS has been rewired properly and is working nicely, now to connect a dummy load and experiment some more.

Sunday was a lovely day, wind dropped so antennas have been put back up and I took the opportunity to tidy up the installation a bit. I also dug out an old fibreglass pole to put the M0CVO HW-20HP back up. I didn't get to do any operating in the end as by the time I had done this and made up a couple of decent patch leads it was time for roast beef and all the trimmings and an evening in front of the TV.

The HW-20HP back up
Putting PL259 and N-Type connectors on coax is also part of the intermediate assessment, so perhaps I should have videoed making up the patch-leads as proof ;-)

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