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[aprssig] sound card VOX

Wes Johnston wes at johnston.net
Thu Sep 16 00:59:48 UTC 2004

I'm wanting to make a PSK31 (ie AGWPE) interface cable which uses a VOX 
type transmitter keying.  I know that Stephen Smith has made an 
interface with extremely quick keyup time, but it requires power from 
the mic jack of the radio.  Since I will likely be using a HT with this, 
I got to thinking...

What if I took the right channel speaker output and tied it to the radio 
mic-input via a transformer.

The took the left channel and ran it thru a cap for DC isolation, thru a 
small signal diode and into the gate of a FET or (or maybe not) an 
ordinary NPN bipolar transistor?  From gate (or base) I'd place a .01 
cap from the gate to ground.  I think(hope) the audio level would be 
high enough to turn on the transistor.  what about using an impedance 
matching transformer as a voltage boost?  I know it won't take much 
current to turn the transistor on... but it will take more than .7v 

Anyone ever tried this way?


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