TM731A.4

Marty Goodman  KC6YKC    June 1992
Home packet BBS:  WD6CMU Richmond, Northern CA
 
I recently acquired both a PK88 TNC and a Kenwood 731a dual band mobile
transceiver.  I wanted to hook the Kenwood to the PK88.  What I found
was that the audio output on pin 6 of the eight pin microphone
connector on the front panel was not the same as the audio that comes
out of the speaker or out of the rear speaker connector.
 
What you get out the audio from the front panel mic connector on pin 6
is an UNSQUELCHED audio.  Kenwood does this, apparantly, to support
their RC10 remote controller for the unit, to allow the RC10 independent
control over the squelch on the audio at the RC10's speaker.  This
causes a problem, for when you feed that into the audio input of the
PK88, its DCD light stays on ALL THE TIME.   The PK88 will receive data
just fine when hooked to pin 6 of the TM731a mike connector, but it will
refuse to key the transmitter because it perpetually thinks the air is
"busy".
 
The simple approach to hooking the PK232 to the Kenwood involves using a
separate cable with a 1/8 in mini phono plug at each end, and run that
between the audio phono connector on the PK88 and the speaker output
jack for "main audio" on the TM731a.   This will allow packet operation,
and is no doubt the approach that virtually everyone uses.  THere are
some drawbacks to this arrangement, tho.
 
Using two cables is a tad clumsey.  Worse, when you plug in the cable in
the rear speaker connector, there is no way to enable the speaker to
audibly check your signal.  It also makes it impossible to make a switch
box to switch the TM731a from packet to audio operation at the flick of
a switch, for as long as the phono plug is plugged into the back of the
TM731a, you CAN NOT enable its internal speaker.   Finally, this
arrangement requires you to adjust the volume control to the right level
and leave it there.
 
What follows is a mod that give you a SQUELCHED, LINE LEVEL audio signal
available on pin 6 of the microphone connector.  With such an
arrangement, you can turn your speaker volume up and down as you like,
and it will not affect the audio going to the packet box.  You can use a
single cable to connect the packet box to the transceiver, and it is
easy to rig up a switch box that switches between the packet box and the
hand microphone. The only disadvantage of doing this mod is that your
TM731a will NO LONGER be compatible with the RC10 remote control device.
CONTINUED IN TM731A.5