Entirely correct. I learned the hard way, spending an inordinate amount of
time on multiple grounding and isolation on my two radio switch board
before realizing that the microphone shields have to be switched together
with the mic high leads.
Once the mic shields were isolated from each other and switched with the mic
high lead, all hum componenets went away. I now have two different vintage
radios playing superbly, no matter which one is selected by the switch
board.
Good luck with the project. 73 de Milt, N5IA
> > Late last night, while setting up for the ARRL SSB contest, I noticed a
fair
> > amount of hum in my monitored microphone audio, while hooked up through
a
> > DVP.
> It is important to isolate the audio return so no other currents
> flow through it. If you have a relay somewhere to switch between
> radios - or your microphone and the output of the DVK - you need
> to use DPDT relays to switch the grounds as well.
>
> Tree N6TR
> n6tr@contesting.com
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