[CQ-Contest] Headset mics

Doug Smith desmith at Telalink.Net
Fri Nov 28 09:56:47 EST 1997

>From: Kenneth Earl Harker <kharker at cs.utexas.edu>
>      Anything in particular we should be aware of before we order one?

I'm using a computer multimedia headset.  (Labtec C-315,though if I were to
do it again I'd get a stereo one -- this one has only one earpiece)  Cheap,
easy to buy (and replace if necessary -- I usually run over the cord with
the chair wheels!), and I get excellent reports.

The Labtecs (and I would assume others) use condenser mike elements; this
means you have to provide DC bias to get them to work.  I put a 10K resistor
on the mike connector between a source of 8V DC (presumably for a DTMF
microphone -- on a TS-940?!) and the center conductor of the cable from the
headset; then, a 1uF 15V tantalum cap (+ side to the headset) from this same
point to the microphone audio pin on the mike connector.  Of course, the
shield of the cable goes to ground.  (and you plug the headphone side into
the jack with a regular 1/8=>1/4" adaptor)  If you use small components, you
can fit the parts in the mike plug and run a short cable to a 1/8" inline
jack; this lets you avoid modifying the headset.  

73 Doug

Douglas E. Smith  W9WI/4 		desmith at Telalink.net.xxx
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