25 Jan 2010

XBM80-2: a 2-way QSO and report

This morning I worked M0DRK using my tiny 60mW XBM80-2 transceiver I designed last week. It uses just 13 parts plus the crystal, earpiece and optional frequency offset switch. My report for Derek was 599 and he gave me 599+40dB. Derek is in the same village. Also monitoring was G4LHI in Huntingdon 32kms away and he reported my signal was as strong as Derek who was running 5W.  In fact 60mW is only going to be about 3 S points down on 5W. I also heard GM3JUD when listening on the XBM80-2 on 3.560, but was unable to raise him.


g4ilo said...

It might be fun to make an SMT version of that. It could be the world's smallest transceiver.

Roger G3XBM said...

Yes that would be fun Julian. The trimmer could be a fixed capacitor, "selected to give a suitable shift when the RX offset switch is closed, making the whole transceiver very small.

Anonymous said...


Looks fabulous! Congratulations on your first QSO with the XBM80-2.

I'm gonna give it a whirl ASAP, but the Eddie (Madman) Muntz in me wants to try it without the audio amplifier! :o)

Thanks again, Roger,

Mike, AA1TJ said...

Sorry...the anonymous reply above was from Mike, AA1TJ

Mike, AA1TJ said...

Wa-hoo! Had my first contact with an XBM80-1 (1 transistor) less than two (unhurried) hours after pulling the components. K1PUG came back to my third CQ with a 559 report from Connecticut (255km). The second QSO with W1GUE (181km)came directly after. Ed (running 5watts) gave me a solid 589. We ended up chatting about QRP for a half-hour! 80mW output/325uW backwave...works FB! Tnx Roger!

Anonymous said...


Last night I carried out some mesurements with my trusty Marconi
Ins TF995 signal generator and managed to hear the hetrodyn of the
sig gen signal down to a level of
approx 15uV rms.
The limiting factors are my hearing the sensitivity of my hombrew crystal hear phone and the impedance miss match of the test set up.
You might get more gain out of the detector stage with a higher beta transistor.
If anyone has got a cheapo DMM with
a transistor test function they could select on test TR2 for the highest beta.

73 Tony G4LLW