[aprssig] TNC-x

[Wes Johnston]

It is open collector.  http://johnhansen.org/media/schematic.gif .   It 
is _now_ open collector with a .1uF cap from collector to ground. ;-)

Wes

Bob Bruninga wrote:

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