[aprssig] Multiple TNC's connected to one radio

al wolfe alw.k9si at gmail.com
Fri Oct 27 13:52:01 EDT 2017

Most TNCs have a pretty high impedance input, like 10k ohms or so.
This being the case, you could probably attach any number of TNCs to
the speaker line from the radio.

If you are concerned about different levels to the TNCs then a couple
of paralleled pots across the speaker output could be used to adjust
the different levels needed. Just tie all the grounds together and
feed the TNCs from the wipers of the pots.

FWIW, most of the TNCs I've dealt with were pretty forgiving regarding
input level. YMMV.

Remember K.I.S.S. The fewer items in the audio line then the fewer
things to go wrong. An audio DA is overkill IMHO.

Al, k9si

>  I would like to connect 2 tnc's to one radio. One would be
> transmitt/recieve and the other recieve only. This would be to test the
> decoding of a couple different tnc's. Am I likely to run into any problems
> connecting the speaker jack audio into 2 tnc's? Would the additional load
> cause me to have to readjust the audio level when I connect/disconnect the
> second tnc? My thoughts are since the speaker jack audio is low impedance (8
> ohm) and the tnc input is much higher (hopefully) is that it will have
> little to no effect.
> Just thought I'd ask before wasting my time making a cable.
> Max KG4PID

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