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[aprssig] TNC Harness Again

Chris Howard w0ep at frii.com
Wed Mar 22 19:49:33 UTC 2006

Is the other end of the cable connected to the TNC?
I mean, does it key when the other end is _not_
connected to the TNC?

The mistake I end up making with these things is
not knowing if the picture is looking at the
end of the cable, or looking at the jack on the device.
For example, you may be shorting between "4" and "R"
instead of "2" and "R" on the radio end of the cable.

If it keys with just the mic plugged in, I don't know.
If it keys with the mike and the phone jack plugged in
then I suspect some cross-up in the mic plug.  If it
keys only when the TNC is also attached then I suspect
a wiring cross-up on the TNC end.

Connector symmetry isn't always a good thing!


On Wed, 2006-03-22 at 12:33, Fred Atkinson wrote:
> Folks, 
>      We checked that harness for shorts and we can't find any problems.  We ohmed it out and checked for shorts to the shield.  Nothing could we find.  
>      The interesting thing is that prior to this, the radio only keyed when we tightened down the screw thread connector.  Now I don't even have to tighten down that connector before it holds the radio keyed.  It does it as I plug it in.  
>      The drawing seems to be correct based upon everything I've read.  You can still view it at http://paws.wcu.edu/fatkinson/APRS/APRS_Harness.pdf.  
>      I don't have the manual on the TR-7850, but I do have it for the MFJ-1270B.  
>      73, 
>                                                Fred, WB4AEJ 
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