Bulletin: KA2567
Vendor:   Kantronics
Subject:  KAM PLUS FEEDBACK FIX

Hello, and greetings from the Rocky Mountians. I just wanted to pass along
some information that may be helpfull to KAM Plus users with Kenwood HF
equipment. This may also apply to other TNC's, as I had the same experience
with the PK-64 TNC. I had horrible audio feedback when I wired the TNC to
the TS-850S/AT's ACC2 plug on SSB. The first step was to isolate the KAM
Plus's power supply from the system, as it was using the same supply. I
found an old 12V 800ma. wall brick that went to a portable TV. It has plenty
of power to supply the KAM Plus. That cut the feedback in half, but the
problem was still there. I have a HT on the VHF port using the 850's supply
so, I began at the ground connections. I found the audio was passing along
the PTT ground line. Since the HT already had a common ground at the power
supply, I was able to cut the PTT ground and still have a working circuit.
Now the feedback was eliminated. Needless to say, this problem was driving
me nuts for a while.
Now, another thing. When you wire any TNC to the Kenwood TS-850S/AT, be sure
to use ACC2 pin #9 for PTT. The english translation in the manual does not
make it clear, but this is the pin to use because it kills microphone input
on transmit at the same time.