[aprssig] Problems with APRS Harness

Fred Atkinson fred at WB4AEJ.COM
Tue Mar 21 17:49:25 CST 2006

     We put the APRS harness together today.  I can see the DCD light flashing when I adjust the audio.  It's behaving like it should.  

     But when I put the microphone connector from the harness in the microphone jack (Kenwood TR-7850) and tighten down the ring, the transmitter keys up continuously.  

     As soon as I loosen the ring, the transmitter unkeys, even if I don't remove the connector.  

     The drawing for the harness can be seen at http://paws.wcu.edu/fatkinson/APRS/APRS_Harness.pdf.  

     Any suggestions as to what might be causing this?  I am using an MFJ-1270B Turbo TNC-2 with the Kenwood TR-7850.  

     I ohmed the harness.  Everything is wired as it should be.  

     I pulled the plug and put my ohmmeter across the PTT (3) and the Microphone Ground (2).  When I issue a connect command to the TNC-2, I think I'm seeing a very brief ground (it's too fast for the meter to track accurately) over and over until the TNC-2 times out.  

     Also (you can tell I've been out of packet for a long time), what is the command to make a TNC-2 display all the packets it hears on the Hyperterminal screen?  


                                                  Fred, WB4AEJ 

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