30 Jun 2009

SixBox QRP 6m AM rig closer to completion

Today I did a full rebuild of the 6m QRP AM transceiver on a much smaller (dead bug style) board so that it will fit in a small diecast (or aluminium) box. In the course of the rebuild I tried out the RX varicap tuning idea which works, but I was unable to move the frequency more than 1-2MHz before the superregen stopped oscillating. I tried a 1N4007 and the collector-base junction of a 2N3904 as varicaps. In the end I decided to use a low cost polyvaricon tuning cap in series with 22pF and this covered 6m plus a few MHz either side. I also ran the PA stage in class C and this seems to improve the modulation. Here is a picture of the SixBox after rebuilding, but before I started the testing. Because of family commitments I shall not be able to finish this now for a few weeks but I am looking forward to some local "DXing" with this around the Cambridge area. It is funny but working local stations with this is (almost) as much fun as working real DX with a proper radio!

1 comment:

Anonymous said...


Great work on the 'sixbox'. I am following it with interest and would like to try and build one in the future.

For low cost varicaps have you considered LED's in reverse bias? Hans Summers has great information on this alternative to normal varicaps, see http://www.hanssummers.com/radio/varicap/led/index.htm

Red LEDs seem to give a good range.

I know many homebrew QRSS transmitters use these for the keying frequency shift.