[aprssig] TNC-x

Wes Johnston wes at johnston.net
Sat Sep 18 17:28:47 CDT 2004

I have a first run TNC-x hooked to a yaesu vx150 HT.  I added a 1uF cap 
in line with the audio since it didn't have one on that revision level 
and that was what a kpc3 uses.  Since it was an HT, I bridged the PTT 
over to the audio with a 2.2k resistor.  All is fine so far.... when the 
tnc keys up the radio, it locks in transmit mode.  Having seen this 
problem before with tiny traks, I put a .1uF ceramic disc cap across the 
PTT to ground inside the TNC-x housing.  The housing is a cast aluminum 
hammond box.  Still, it locks in transmit.  I hooked it to another 
radio, a radio shack htx252 which also uses the same 2.2k ptt setup 
(just like an HT).  It too locks on TX. 

The DB9 I'm using for a radio data plug is wired the same as a kpc3 (so 
I can use the same cables), it is mounted to the metal box.  The tnc is 
grounded to the box by the three mounting screws in the corners of the 
PCB.  There are no wires exposed except for the radio cable and the USB 
cable.  It's actually a very neat (ie clean) setup.

Any other suggestions?


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