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[aprssig] Mic-E and HTs

Wes Johnston aprs at kd4rdb.com
Mon Dec 12 13:03:55 UTC 2005


Ahhh.... but perhaps Scott is talking bout the tiny track _sensing_ the
mic line.  First it has to sense what the status of PTT is so that it
can know when you release PTT so it can inject the packet.

Wouldn't this be an integrating op amp?  Just bypass any frequency above
 100hz, right?

Wes

Stephen H. Smith wrote:
> 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.
>>
>>Scott
>>N1VG
>>
>>
>>
>>
>>_______________________________________________
>>aprssig mailing list
>>aprssig at lists.tapr.org
>>https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig
>>  
>>
> 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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