A long time ago, 2009 or so, Ham Radio Outlet was offering the RC-D710 control head and TNC for a very reasonable price. This is the identical control head used on the Kenwood TM-D710 mobile transceiver. It includes a built-in Terminal Node Controller (TNC) and APRS software.
I bought one thinking I could use it with an existing mobile radio for APRS. I also bought the PG-5J interface that provides the 10VDC @ 360mA power supply to the control head/tnc and the RX/TX audio signals needed to connect it to a radio. It was yet another project that I hadn’t gotten around to while working full time.
Recently I gave a talk about APRS at a SOARA Saturday gathering and I was hoping to have the RC-D710 working so that I could demonstrate it during my talk. Unfortunately, I ran out of time and didn’t get to it before the meeting.
After SOARA Saturday I got the RC-D710 back out on the bench. I set it up using the Kenwood interface and cabling. The PG-5J does what it is supposed to and I was able to connect the RC-D710 to an ID-880 Radio using the Data jack on the ID-880, however this setup was less than portable. I found an article by Bob Bruninga, WB4APR (SK) about how to use the RC-D710 with any HT. That was just what I was looking for.
There is also a commercial product that interfaces the RC-D710 to a mobile transceiver or handie-talkie. This directly replaces the Kenwood PG-5J interface.
I set out to build the circuit that Bob described to use the control head with a spare Icom IC-91AD handie-talkie.
I wanted to confirm the current requirement so I used my bench supply and wired it to the DC Input to the control head through the RJ-45 connector. To my dismay, nothing happened! There was a few milliamperes of current flowing, but the control head would not fire up!
After some head scratching I noticed a jumper on the RJ-45 in the circuit between pins 4 and 7 (Kenwood numbers RJ-45 connectors the opposite to how I’ve always numbered them) In 25-pair color-code terms, the orange and white/blue wires need to be jumpered.
Now that I have the control head powered up, I built the simple interface circuit for sending receive audio to the TNC and combining the PTT and transmit audio signals onto a single pin, as most non-Kenwood HTs require along with the power supply.
To facilitate the connections between the RJ-45 cable, power supply, and handie-talkie, I used one of these neat adhesive-backed circuit board strips that my friend Horst, KD7JHR gave me. For the interface to the HT, I have a standard that I use with 3.5mm TRS connectors. Tip = TX Audio, Ring = RX Audio, and Shield = Ground/Earth.
For the power supply, I used an LM2596 based switch-mode voltage regulator to keep the heat dissipation low. I had tested using an LM-317 voltage regulator but it would require a large heat sink.
Lastly, I designed a small case to house the regulator, 3.5mm HT interface jack and the wiring PCB.
If you happen to run across a used RC-D710 control head or a control head from a broken TM-D710 radio, you might try this setup with a spare radio or handie talkie.
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