Subject: Wiring TNC to FT-2400

The radio is a FT-2400 with a RJ-45 plug for the
microphone. An RJ-45 is a eight pin plug that is
not common among radio gear. By the looks of it,
it is popular among business radio gear (E.F.
Johnson 800 Mhz and Motorola mobiles).

Well, you can get this hard-to-find 8 wire plug from
Radio Shack for some $6.50. It is listed as a 279-440
in their telephone section.

The connector is unique in that the method of connection
for the wires is identical to the computer ribbon. it has
push down knives that cut the insulation of the telephone
wire. The push-down connections also happen to be perfectly
spaced for computer ribbon cable. You can buy the short
piece of 25 conductor ribbon cable and slice for just
eight conductors. When you properly line it up, it looks
and acts perfect for the job.

You can even do without the use of pliers! I manually
pushed in the ribbon thru the push-in points. They did
the job well.

Looking at the furnished schematic diagram and the TNC
wireup then is a simple matter of soldering the necessary
connector for the TNC.

Some Points to Ponder

1.Remember that the computer ribbon cable is unshielded.
It might not be suitable if you are using an mobile
antenna nearby to the equipment. At the installation
site, we had a Comet 2x4 up one story above us and
had no RF Feedback or any RFI problems.(using 50
watts right next to you isn't good practice, anyway).

2. In the infinite wisdom of Yaesu, the Receive Audio
thru the mike plug is disabled when you install an
external speaker. I don't know why. It didn't help
us out when we first tested the cable. If it wasn't for
the jumpy bargraph on the 1278 showing low packet audio,
we wouldn't have figure out what was happening.

3. The Receive Audio is adjustable thru the Volume
Control. Another interesting thing for Yaesu. Why?

4. As per Yaesu documentation, you should use only a
TNC with hardware DCD inside. Units such as the PK-88
will never work thru the mic plug. The PCB-88 would
work. TNCs like the MFJs and the KPC-3 (CD SOFTWARE only)
should work fine.