[aprssig] Mic-E and HTs

Stephen H. Smith wa8lmf2 at aol.com
Mon Dec 12 02:21:48 CST 2005

scott at opentrac.org wrote:

>Does any existing Mic-E type hardware work with HTs that don't have a
>separate PTT line?  I came up with a circuit that works OK, I'm just curious
>if there's something else out there already.
>aprssig mailing list
>aprssig at lists.tapr.org
Yes.  The TinyTrak has an arrangement to simulate the 
"ground-the-mic-element-to-draw-current-and-transmit " arrangement used  
for 2-wire mics on hand helds. 

All it is is a 2K resistor between the PTT line (open collector)  and 
the audio output line of the TT.  (This is (the "R8" that is endlessly 
discussed and misunderstood  on the TinyTrak mailing list and elsewhere). 

 You connect the audio-out line only of the TT to the HT.  When the TT 
keys (saturates the open collector to ground), DC current flows out of 
the radio's mic jack through the resistor to ground and keys the radio,  
without shorting out the audio to ground.  

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