The metal shield cover on the 2m module was not flat but slightly raised at the edge. I have pressed this back on and the problem seems cleared. So I guess it was contacting or coming close to the circuit board on the control module, perhaps that giving the feedback loop for RF. Question is - could any damage have done if it had contacted the vias/pads on the board there?
- Richard On Wed, 5 Feb 2020 at 21:01, Richard Corfield <[email protected]> wrote: > I've done some further tests and proven the problem is with the MH3. So > I'll have to take that apart and look for the problem. > The radio is fine with little earbuds/mic plugged in via splitter cable. > Swap out the mic on the earbuds with the MH3 and leave all the rest the > same and it goes wrong. > > Thanks > - Richard > > On Wed, 5 Feb 2020 at 15:29, Nr4c <[email protected]> wrote: > >> Turn down TX Monitor volume. >> >> Sent from my iPhone >> ...nr4c. bill >> >> >> > On Feb 5, 2020, at 5:23 AM, Richard Corfield < >> [email protected]> wrote: >> > >> > I had issues with RF feedback on the MH3 during the UKAC SSB 2m contest >> > last night. It seemed intermittent. Result was terrible noise in Monitor >> > output (my headphones) and to the other station, so it affects the audio >> > input. With experiments at the time and this morning: >> > >> > >> > - Occurs when RF power is increased above 0 and when Mic Gain is >> > increased. I could operate with Mic Gain set low, obviously at reduced >> > power out. (Indicative of a feedback loop) >> > - Occurs with a dummy load. (Also when I moved the antenna away last >> > night). So is the loop internal or is it so sensitive the small leak >> from a >> > dummy load is enough? >> > - Does not occur if I feed a stage Mic In through a field mixer (kit I >> > have to hand). The field mixer claims an output impedance of 150R and >> is >> > running at mic level to match the MH3 allowing same gain setup in the >> KX3. >> > Mic Bias is turned off in this case. >> > - Does not occur on HF into the dummy load. >> > - Manifests as buzzing on 2m FM >> > - May result in phantom button presses on the KX3 Mic (I didn't think >> I >> > knocked the dial) >> > >> > As an aside - one station last night was loud enough to activate the >> "RX" >> > indicator which I take to be input overload. S meter was well over S9 >> but >> > not at the top. I didn't see anyone else at the site, unless they were >> > hiding the the woodland carpark but I saw no light there or on the >> summit >> > behind me. I hit ATT, should have swung the beam to try to null them. >> But I >> > guess the ATT and even maybe the input protection is after the 2m >> module's >> > input? >> > >> > My thought is I need to inspect the wiring in the mic. Or could there be >> > anything else I need to check? >> > >> > Thanks >> > - Richard >> > ______________________________________________________________ >> > Elecraft mailing list >> > Home: http://mailman.qth.net/mailman/listinfo/elecraft >> > Help: http://mailman.qth.net/mmfaq.htm >> > Post: mailto:[email protected] >> > >> > This list hosted by: http://www.qsl.net >> > Please help support this email list: http://www.qsl.net/donate.html >> > Message delivered to [email protected] >> >> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
