[Ham-Mac] Noise Canceling Microphones (somewhat off topic)

[K6LMP]

I have a mobile transceiver that I use, part of the time, in a very 
noisy environment -- a Swiss Army surplus troop carrier called a 
Pinzgauer.  It is essentially impossible to talk on the radio while the 
vehicle is in motion, due to the very high ambient noise level.  I have 
a pair of active noise suppression headphones that make listening 
feasible, but I don't have a good solution for noise cancellation into 
the microphone.

Two alternatives seem viable.  First, there's the Astatic 636L handheld 
microphone, which sells for about $40.  Does anyone have any experience 
with this unit?

Second, I found a circuit diagram online for a noise canceling mike 
setup using two RadioShack electret mikes, fed through two small and 
simple transistor amplifiers and with outputs merged 180° out of phase. 
One mike is apparently arranged pointed toward the mouth; the other 
away from the mouth, to pick up ambient noise.  In theory, the anbient 
noise component cancels, leaving only the voice.  This was apparently 
written up in the December 2000 issue of QST, which I don't have.  If 
anyone has experience with this setup, I will order a copy of the 
article from ARRL.

Thanks in advance for any comments.



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K6LMP
Lew Phelps
Pasadena, CA