The FT-847 provides a 6-pin mini-DIN connector on the rear panel for packet
operation. Before I ran out and hunted down a 6-pin mini-DIN connector,
I remembered that PS/2 keyboard/mouse connectors are also 6-pin mini-DIN,
and figured I should try using a commodity part from a computer store, if
possible. I suppose I could have used the Yaesu accessory cable CT-39,
but I didn't want to go to the trouble.
I bought a 6-foot PS/2 keyboard extension cable for $4 at a local computer store, and used an ohm-meter to verify all six pins were connected through. Then I cut off the female end, leaving a few inches of cable attached. As expected, I discovered the cable uses 6-conductors plus a shield, and I used the ohm-meter to figure out which wire-color corresponds to which pin-number. Since the PS/2 connections don't use a couple of the pins, I was afraid that the cable would omit these connections entirely, and I was also concerned that the connector shell would be internally connected to one of the wires. Neither of these turned out to be the case; the $4 extension cable was ideal.
The TNC I'm using is a PK-88 at 300/1200 baud, so I wired up an 8-pin connector
to the mini-DIN cable, connecting the cable shield to the signal ground.
My first test, receiving, worked as expected. So, I entered calibrate
mode on the TNC and keyed PTT (pushed 'K' for the PK-88). Nothing.
I checked the PTT line, and the TNC was pulling it to ground, but the radio
wasn't keying up. A quick look at the FT-847 schematic suggested why;
the packet data input level inhibits PTT if it is too high in amplitude
! It doesn't appear to be explicitly stated anywhere in the FT-847
manual. Anyway, I turned the TNC output amplitude all the way down
(which I should have done in the first place), and PTT started working as
expected. I finished the calibration and was on the air.
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Dana, K6JQ. Last updated: 15 June 2001