On Feb 20, 7:21 pm, Mozzy <d...@account.com> wrote:

> On the other hand, you can get a cheap electret microphone designed to
> be worn in the ear (as a phone-recording microphone) which is remarkably
> resistent to cellphone RF.

Generally the way intereference gets in is by speaker or power or
signal wires acting as antennas. If a wire doesn't need to carry a
high speed signal, you can bypass it with an RF choke in series and/or
capacitors to ground. And put the circuit in a shielded enclosure.
Chokes, and perhaps coaxial microphone cable, should help quite a bit.

With GSM phones, the worst interference seems to be when the network
is getting ready to ring them. In fact, I can often tell when my
phone is about to ring because of what happens to my computer
speakers, or car radio. Chances are the phone won't be heard in its
own headphone because it probably has it's audio jack bypassed with
chokes and its amplifier not only well shielded, but also muted at
this point. And nobody is yet on the other end to hear if the
microphone is being interfered with. Presumably a phone that does
voice recognition could even know exactly when it is transmitting its
stronger pulsed signals, and thus if necesssary not listen right then,
to avoid confusing itself.