[aprssig] KPC3+ and U800 not talking

Bill Herrmann bherrman at spro.net
Thu Mar 10 01:06:02 CST 2005

At 08:38 PM 3/8/2005 -0500, n1iic Jason Greene wrote:
>Greetings, All. I am trying to get my Ultimeter 800 talking with a KPC3+ 
>8.3 (and 8.2) and no matter how I configure or connect, I can't get the 
>TNC to hear anything. The  U800 is sending correct data.

On 8.3 you should be able to use either port. On 8.2 you can only use the 
DB25 port. (The hardware is there, but the firmware doesn't support it till 


I'm assuming you checked that the U800 is sending $ULTW at 2400bps.

>I have the GPS string in there for testing, and the GPS didn't work 
>either. It has worrked before, though.

The GPS is probably sending at 4800bps.

>Everything is at 2400 baud, and when I connect the Ultimeter to the 
>computer, APRS (or any com program) can see it fine.
>So, Data is coming out the end of the wire, The computer can see it, now

The important thing here is where is it coming out. If you can plug the 
cable directly into the computer that means that the cable plus U800 is 
wired as a DCE device. (since the computer is a DTE device)

>I have tried every possible way to connect the U800 to the TNC, both 
>through pin 2(data) - 6(gnd) on the radio port and both pins 2 and 3 
>(data) and pin 5(gnd) on the DB9 of the DB9/DB25 cable.

Which pin of what size connector did you wire to pin2 on the radio port? 
(connector size is important here because the meanings of pins 2 & 3 are 
reversed on a 9 pin vs. a 25 pin connector.)

To plug the U800 into the computer (25 pin) connector you'll have to have a 
null-modem adapter or cable between the cable that works with the laptop 
and the TNC.

To be successful with RS232 you pretty well have to stop and look at how 
the devices are wired (DCE vs DTE) and think about the pin meanings not 
their number especially if you are mixing 9 pin and 25 pin connectors. (I 
mentioned above that 2&3 swap meanings between those. A 9 pin to 25 pin 
cable that swaps the leads between 2&3 is a "straight-through" cable.)


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