2 Nov 2011

Chirpy (XBM10-2) improvements

28MHz "Chirpy" Transceiver with tuned antenna match
In the last day I  have made some changes to my ultra-simple CW transceiver for 28MHz. Power output now is around 120mW (was 60mW) and the RX sensitivity about 3-4dB better. Both changes are a result of better matching the tank of the oscillator/mixer to 50 ohms using a tuned circuit with a suitable tap rather than a 100uH choke. At the moment the component count is 14 total (excluding crystal earpiece and key). although this could be reduced to 12 if a suitable single component inductor/capacitor with link winding was substituted for the only tuned circuit. The receiver is working and I copied an SV station and K1TG on 28MHz just now. The TX still chirps though. Now I am looking for some further 2-way QSOs (3 so far with best DX IT9QAU/QRP at 1414kms).

4 comments:

Julian Moss said...

Sounds promising, Roger. Hopefully I'll be able to make the changes to mine tomorrow. Haven't had any replies to my CQs yet.

FuzzyUK said...

Don't you need a bypass capacitor across the PSU rail?

Roger said...

Not if the PSU supply is a sufficiently low impedance as is the case with most rechargeable battery packs.

FuzzyUK said...

That not the point. The + rail could be picking up RF between the circuitry and the battery/PSU. Chirp is quite often due to some form of RF feedback. Worth trying say a 470pf capacitor.