[aprssig] TNC-x

Bob Bruninga bruninga at usna.edu
Sun Sep 19 08:08:33 CDT 2004

I havent seen a TNC-x, but is the PTT an open collector NPN or
just an I/O pin on the chip?

On Sat, 18 Sep 2004, 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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de WB4APR at amsat.org, Bob

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