Hi Andy, Jerry and the forum,
Thanks for your suggestions to tame my G6LBQ transmitter instabilities.? I haven't had time until no to respond more than briefly. I found that the speaker-mic I was using was un-shielded and acting as an antenna, coupling RF back into the Q5 stage.? It probably didn't help that the thing was sitting on the bench opened up. An alum sheet case lid may have helped.?
Regardless, I have ditched the speaker-mic and have reverted to an inbuilt electret condenser mic element, built right in at the mic amp input.? What confused me is that the RF feedback did not decrease when I took +12v Tx off the mic amp stage. So the speaker-mic cable must have been coupling RF back into Q5, not the mic amp.??
I made up some brass plate shields to fit over the first mixer (ADE-1), MC1350 stage (probably not necessary as this stage is not powered in transmit, but good practice for oscillator shielding anyway), and mic amp including the electret mic.? If I turn up the PA bias sufficiently high, the RF feedback returns.? I will do more work on shielding the PA stage, and band pass filters.? For now, the little rig appears to be usable, so I'll try it for a while 'in the field' before further work.? ? ?
On Sunday I?strung?up?a 40/20m trap vertical in the back yard, and stood under it, holding the G6LBQ walkie talkie, on a LiFePO pack, listening to 20 and 40m. On 40m it is as sensitive as anything else I've built.? 20m is just dead all the time.? But band conditions were terrible, I ran out of time, and didn't attempt to try to make contacts.
Hopefully I'll get up to a SOTA summit soon for a real test of this G6LBQ build.
73 Paul VK3HN
Paul VK3HN