Thanks to the pandemic I hadn’t done any SOTA for almost two years but I have been busy homebrewing. One of my recent projects has been a two-band (20m/40m) CW rig specifically designed for SOTA. I built it into a “Gift in a tin” box which had had a children’s sewing kit in it. Instead of an LCD display it uses a few LEDs to show where you are in the band. It’s powered by 10 AA NiMH cells. When I got home the batteries were barely depleted so the spares I had with me weren’t needed.
I finally was able to try it in the field yesterday. I live in Ilkley so the top of Ilkley Moor (aka Rombalds Moor G/NP-028) is about an hour’s walk and there’s a nice comfy spot by the wall close to the trig point. I can bungee the 6m pole and not have to talk to any passers by so it’s the obvious place to go. The weather was pretty good too. [Later on while I was walking with my daughter home from school the heavens opened and we got absolutely soaked. I was very glad it wasn’t while I was on the hill.]
I’m pleased to say it worked well with 8 contacts on 40m followed by 5 on 20m. I then switched back to 40m - the rig defaults to the QRP calling frequency where I heard G3XJS calling CQ so I had a nice chat with him. I knew I recognised the callsign so was pleased to have the QSO - he’s the G-QRP Club Communications Manager.
So thanks to all the chasers who put up with my terrible sending and inability to receive anything slightly too fast.
The RX is an image cancelling direct conversion with 200Hz filter. It’s controlled by an ATtiny with built in keyer. The oscillator is an Si5351A. The TX is 5W Class E with a relay switching between the LC/LPF networks for the two bands. It’s surface mount built on 4 home made PCBs.
I’m very impressed. I’ve made a couple of QCX kits but designing one from scratch - and an advanced design by the sound of it - takes things to another level.
Well done Richard, as I put in my reflector post on Thursday, it doesn’t really get any better than contacting fellow enthusiasts on a device you’ve devised yourself.
The design has a lot in common with the QCX - Tayloe detector, all-pass op-amp phasing filter, 200Hz audio filter are very similar - so it’s not really designed from scratch. The software is near enough all mine though (although the Si5351A driver did come from Hans Summer’s example code). The class E amplifier design was created in Tonne Software’s ClassE but I did have to tinker a bit to get it right. I think most electronic designs start with building blocks from other people and then you make changes to suit your needs.
I shall probably send the design to Sprat eventually and put it on my website.
I spend far more time home brewing than actually going on the air. That’s why my morse is so rubbish! I’m impressed with your results with such simple gear.
I tried my rig with a PP3 battery and got about 1W out. I realised it was an old battery so with a fresh one it was just under 2W. 10 NiMH AA cells gave me 4.3W on 20m and 4.7W on 40m.
For comparison I then tried it with the shack PSU and got 4.8W on both bands. All the batteries give slightly less output on 20m than 40m - the PA is less efficient on the higher frequency so it draws more current. The PSU can supply 30A peak so it supplies 13.8V regardless of the current whereas the batteries all have an internal resistance.
