[aprssig] TNC-x

Wes Johnston wes at johnston.net
Sat Sep 18 20:56:13 CDT 2004

Well, I found the solution... I moved my .1uF cap from the radio plug 
all the way back to soldering it onto the leads of Q1, the PTT 
transistor.  Working fine now.  Now to get deviation set.


Wes Johnston wrote:

> 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?
> Wes
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