IRLP Cables

Connecting IRLP node to mobile transceiver

IRLP Node number 4214 has employed different VHF/UHF transceivers, beginning with a somewhat unreliable Yaesu FT-7100M and moving on to a Yaesu FT-8000R. Several people have asked how I connected these radios to the node PC. Devising a suitable cable should be well within the capabilities of any radio amateur, but if you would like to see my particular method — then here goes.

First of all, I chose transceivers with their own packet radio "DATA" port. This type of radio happens to include all the connections needed for an IRLP connection in one place... audio in, audio out, press-to-talk and receiver squelch. To some extent, the cabling of packet data ports on mobile transceivers has been standardized by the Japanese manufacturers, based on a 6-pin mini-DIN connector — so you might have success with brands other than Yaesu. Icom and Kenwood seem to use the same 6-pin mini-DIN connections, but Alinco goes its own way with a combination of mini-jacks.

FT-8000R Data Jack

The only problem with the 6-pin mini-DIN is that the pins inside the male connector are tiny and very difficult to solder reliably. I took the easy way out and purchased a pre-wired cable —actually it was a Radio Shack 6 foot extension cord for PS/2 keyboard or mouse. If you don't want to solder the 1/8" audio plugs or DB-9 female connector yourself, you can use the same approach. Just purchase suitable cables, then cut off the end that isn't needed, or cut the cable in half if it is symmetrical. For example --

6-pin mini-DIN male

RS part number: 26-149, 6 ft extension cord for keyboard or mouse. Cut off female end.
RS part number: 42-2387, 6 ft 1/8" stereo to 1/8" stereo cord (shielded). Cut in half
RS part number: 26-117, 6 ft serial RS-232C cable (shielded DB-9 M to DB-9 F). Cut off male end.

After cutting the cable, check which colored wire is connected to which pin using an ohmmeter. The table and diagram below show the cable colors for the Radio Shack extension keyboard / mouse cable that I used — but your colors might be different!

Here are the connections required between the transceiver's 6-pin mini-DIN connector, the 1/8" stereo plugs for the Line In/Out jacks on the computer's sound card and the DB-9 female connector that runs to the IRLP Interface Board in the PC.

Mini DIN	Label	Color	Function	Connect to
Pin 1	PKD	Black	Tcvr audio in from node PC	To PC Line out via 20 kohm pot
Pin 2	GND	Brown	Ground, also connect to cable shield	DB-9 pin 6, line in/out shields
Pin 3	PKS	Red	Press to talk from node PC	DB-9 pin2
Pin 4	RX9600	Orange	No connection (9600 bps packet out)
Pin 5	RX1200	Yellow	1200 Bd packet out, audio out to node PC	DB-9 pin 8 for DTMF, also connect to PC Line in
Pin 6	SQL	Green	Carrier operated squelch to node PC	DB-9 pin 7
-	-	-	-	DB-9 pin 3, AUX-1

The diagram below shows how I connected my cables. The block marked "Interconnect" uses a Radio Shack # 274-679 12-position European-style terminal strip (aka choc-block connector), but you could also use a barrier strip or terminal strip to solder the connections.

irlpschm.GIF (84722 bytes)

As in any project combining low level audio and radio frequency transmission, be sure to connect all cable shields to "GND". The left and right audio wires in each of the 1/8" stereo cables are soldered together (red and black). The PTT line runs through an on-off switch so the transceiver does not come on at PC power-up. This is also a convenient place to disable the transmitter for testing etc.

Use of the standardized 6-pin mini-DIN packet connector makes it relatively easy to change from one mobile VHF/UHF transceiver to another. But if you do change transceiver, don't be surprised if the audio levels you need to set on the sound card are quite different from before. In some radios, the PKD "packet audio" is applied directly to the FM modulator without any filtering or limiting.

- 73 de Malcolm, NM9J, Sept 6 2004

G3VNQ-NM9J amateur radio site, 05-Jun-2007