On Feb 22, 3:31Â*pm, sorry-spammers ""w9wi\"@(sorry-spammers)" wrote:

Ah. Â*I've not tried that circuit on VHF, let alone UHF, let alone a phone, but I'm quite familiar with the mess a mobile phone can make of a
microphone signal!

Yep, strangely the arrangement sans C2 was fine for 70cm doing 4W
FM... but not okay on 900MHz doing ~100mW GSM signalling. The joys of
GMSK at 9600 baud.

(I work for a TV station. Â*Our newsreaders used to think if they turned off the ringer, they could leave their phones in their pockets while on the
air. Â*Two or three interrupted stories later, they learned to leave their phones in their office....)

Hmmm, buzz buzz... "Ohh, sorry about that interruption, that was my
phone." Ooops!

On amateur radio, it can't hurt, and can only make your signal better
IMO... I think Heil and other companies do a similar thing for
electret microphones.

What value are you using? Â*(I would suppose something on the order of 500pF would be adequate. Â*I've seen people use rather large values in an attempt
to reduce HF audio response..)

Usually some nominal value... the doc I linked to recommend a 10nF. I
have no idea what some of them are using, but anywhere between 10nF to
100nF would be sufficient.

If you want to be truly scientific about it, you can pick a frequency
and dimension the capacitor so that Z=1/(jωC) is sufficiently high to
not matter 10kHz and approaching 0Ω at the frequency of interest. I
like the suck-it-and-see approach for this application however. :-)