[Elecraft] RF feedback into MH3 mic with KX3 on 2m

[Nr4c]

Yes. Headphone to mic distance gets short and feedback can happen from leakage. 

Sent from my iPhone
...nr4c. bill


> On Feb 5, 2020, at 10:44 AM, Richard Corfield <richard.corfield at gmail.com> wrote:
> 
> 
> Even with monitor running into headphones?
> 
> I was running the contest with monitor off at first, but I turned monitor on only in response to my contact telling me my audio was garbled. That said, I initially wondered if the garble was due to frequency drift not feedback. Though if it was a monitor problem it would also manifest on HF and through the vocal mic?
> 
> I can try though. I know the headphones leak, closed as they are, as I've picked up notification beeps when using the field recorder and monitoring on headphones while recording my voice.
> 
>  - Richard
> 
> 
>> On Wed, 5 Feb 2020 at 15:29, Nr4c <nr4c at widomaker.com> wrote:
>> Turn down TX Monitor volume. 
>> 
>> Sent from my iPhone
>> ...nr4c. bill
>> 
>> 
>> > On Feb 5, 2020, at 5:23 AM, Richard Corfield <richard.corfield at gmail.com> 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
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