Good question .. others will answer it but I just had to comment thus...
I have had serious rf pickup problems with all of my radios and several
different kinds of microphones. The root problem is that I have ladderline
coming right into the shack but I can't change that.
Microphone cable shields ought to protect the front end of the audio chain
in the radio but very often the microphone cable shield is *not* directly
grounded to the chassis of the radio. There is a suggestion on the Heil
website that one can often solve rf pickup problems in the microphone by
making sure that the microphone cable shield is *directly* connected to the
metal microphone connector. Heil makes the point that often the mic
manufacturer connects the cable shield to one of the pins on the mic
connector but leaves it to the radio manufacturer to connect that pin to the
chassis of the radio.
The radio manufacturer designer does connect this pin to the chassis but
that involves an extra inch or two (or more) of wire in the ground circuit
and, especially at higher frequencies, that can be enough to allow rf on the
outside of the mic cable shield to couple to the wiring inside the shield.
I had that problem in spades on 10M and 6M with my K3. I fixed it by
connecting the mic shield within the mic connector directly to the metal
connector shell which, of course, screws onto the mic connector on the radio
which is bonded to the chassis. This improvement was suggested by Heil on
their website.
What kind of mic am I using? An Elecraft MH2 .. which, I think, is made by
Heil. Go figure.
I'll bet I am not the only one with rf-in-the-mic-circuit problems. So, I
thought I should pass along my experience.
Don K7FJ
Does the Elecraft require a microphone ground as well as the usual ground
for its microphone connector? If so, should it go to to pin 7 or 8 on the
Elecraft mike connector? If not, are both ground connections necessary to
be made to pins 7 & 8 in the connector?
Thanks,
Lew W7EW
#1560/1561
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