Saturday 15 May 2010

Homebrewed Whispers

I realized recently there's something of a gap in my experience - so I determined to fill it...

Most of my homebrew activities are in QRP rigs for CW. In consequence, I've little experience of generating DSB/SSB signals. Sure - I've played with mixers in receivers - but never in transmitters. That's the hole I decided to plug.

I made a simple balanced modulator, using "Ed" Skelton's circuit as a jumping-off point. Here's the result...



OK - all very interesting - so now I can generate DSB signals, what shall I do with them? I know - I could follow Bill n2cqr's lead and work some DSB WSPR. I have played with WSPR before (both with my Softrock SDR and with my nearly new FT817), but never with a homebrew rig. So - I looked out a little PA I built a while back as a bench amplifier...



I generated a stable local oscillator signal using my USB Synth from SDR-Kits and added a 80/40m low-pass filter (previously built for my HEXFET PA Brick for the SDR) to keep my emissions clean. The whole lash-up is seen below (I've added some labels so you can spot all the elements!)...


I measured the output on the 40m band as 20mW (13dBm) and set up the WSPR station details accordingly.

Delighted to be received almost immediately by Jaap, pa0o, in Zuidwolde, Netherlands...



This really is whispering - homebrewed rig, 20mW output (10mW really, given that my lower sideband is just somebody else's QRM) - great fun!

...-.- de m0xpd

1 comment:

  1. Well done. One of the things on my To Do list is to make a homebrew WSPR rig too. Probably after the Sporadic-E season is over I'll have a go.

    ReplyDelete