From:  Mark Camp   KE0KO   St. Louis, MO

I recently purchased a Kantonics KPC-2 TNC for use on packet.  I wanted
to use it with my Yaesu FT-23R handie talkie.  After several hours of
frustration and trying every wiring combination known to modern man, and
after seeking advice from several sources, here is the way I got mine to
finally work.  

READ ALL OF STEP 1 BEFORE DOING ANY WORK!

1.  In the KPC-2 users manual, Kantronics has a section about a built
    in isolation circuit that the KPC-2 has so that it can be used
    with handheld radios which have condenser mics.  They tell you
    to go inside the KPC and locate J1 near jumper Q, cut J1 and
    add J2.  
    
    I did this, but it did not work with my Yaesu FT-23R.  So, before
    you try to modify the KPC, try the steps below FIRST.

2.  Buy a  1:1  audio isolation transformer.  Radio Shack sells one
    for  $3.49.  The part number is  273-1374 .

3.  The transformer I bought at Radio Shack had the following color
    configuration:
    
      white   o----------  ----------o   yellow
                        |  |
                        |  |
                        |  |
                        |  |
                        |  |
      black   o----------  ----------o   red
      
4.   Take the line coming from the KPC-2 that has the five wires.  I
     clipped off the red and green leads as well as the silver shield.
     Solder the leads to the transformer as follows:
     
                   KPC color             transformer color
                   
                    white ----------------- white
                    
                    black ----------------- black
                    
                    brown ----------------- red
 
5.  Now, take the yellow wire from the transformer and solder it to the
    center (tip) of the FT-23R microphone connector.
     
You can then figure out some way to mount the little transformer.
I mounted mine in a very small plastic box and have all the solder
connections in the box.  I soldered a larger wire to the yellow wire,
then soldered the larger wire to the mic plug.

Also, I removed jumper K3 inside the KPC.  K3 controls the AFSK level.
You may not have to do this, but mine works fine.

By the way, I called Yaesu 3 times and got three different answers as 
to how to solve the problem.