Modifying Kenwood TK860 TK862 TK760 TK762 Radios for Link Use
By Kyle Yoksh K0KN
Converted for Repeater-Builder by WA1MIK

Click on any of the photos for a larger view.

I purchased a Kenwood TK860 and TK862 UHF Mobile radio in late 2011 to use for RF linking purposes. The radios did not have the KCT-19 accessory cable included. This cable was designed to carry quite a few signals in and out of the radio, mainly for commercial use or repeater connection. The TK760 and TK762 VHF models should be able to be modified in a similar way, although I have not yet tried it.

Note that the radios described here are NOT the G model.

tk860-front.jpg - 131621 bytes

Before purchasing two KCT-19 cables ($21 each + shipping in 2011), I checked out the option connectors inside the radio (CN1, CN2, CN4, CN201). None featured a PL-based COS signal (sometimes called TOS). The only signal available to the KCT-19 was COS (Carrier Operated Squelch), also sometimes called COR. I wasn't about to spend $21 per radio for an accessory cable that didn't have a PL-based COS.

All of the the necessary connections are available on the rear side of the faceplate. Remove the upper and lower covers, and then remove the faceplate from the radio. Leave the ribbon cable to the faceplate attached. You may also want to unplug the internal speaker.

Carefully drill a 1/4" hole just above the faceplate ribbon cable slot. This will be used to carry our wires from the faceplate area out to the rear panel. Use a vacuum or compressed air to ensure that all of the metal filings have been removed from the radio.

tk862-top.jpg - 120699 bytes I found some scrap wire lying around with a 1/4" outside diameter, and cut a one foot piece. The jacket makes a good conduit for running wires from the front of the radio to the rear. A piece of vinyl tubing could also be used. Route the tubing from the 1/4" hole in the face area to just outside the rear panel, underneath the power leads.

I recommend using shielded wire for the mic input and audio output lines. A good (free) source of shielded wire is old computer monitor video cables! Each monitor cable has about 20 feet of shielded wire, and about 30 feet of stranded hookup wire. Most monitor cables also have one or two ferrite cores molded into them that might come in handy sometime.

tk860-faceplate-thumb.jpg - 44292 bytes Here is a picture of an unmodified TK860 faceplate. Note that some TK860 or TK862 radios may have had an accessory voice scrambler board installed. My TK862 still has wire jumpers where the input and output of the microphone line and audio out lines were connected to the scrambler. The scrambler was removed, and the jumpers connected together to restore normal operation.

Take a look at the faceplate. Click on the picture to see the full-size image. I have circled the appropriate takeoff points in red. The PL-based COS signal comes from a solder pad labeled UM (UnMute). This line is active high (+5v) when the receiver is unmuted. In other words, this line functions as both a COS and TOS, depending on how you've programmed the radio. In my opinion, this is where the KCT-19 squelch line should have been connected by Kenwood.

Next, look for the Fixed Audio Output. This is deemphasised audio at a low fixed level (not affected by the volume control). The capacitor marked with C105 in the picture was missing in my TK862, and a discrete capacitor was in its place. This was the point where the scrambler board broke the receiver audio circuit.

PTT is taken directly from the mic jack itself. Note that the PCB is even marked with PTT, and an arrow to the solder pad.

Mic input is connected to a pad near the mic jack labeled TXAF (Transmit Audio Frequency).

Underneath the mic jack are two large solder pads for ground. I decided to ground both of my shielded lines here, one to each solder pad. Note that the TK860 and TK862 do not require separate grounds for PTT, audio output, and mic input. All grounds are all at the same potential.

To enable front-panel or field programming of your TK760 or TK860, connect a small jumper across the two points shown in the picture. You will also need to enable this feature via the programming software before field programming will work.

Once all of your lines are connected, carefully reassemble the faceplate, and reassemble the radio. Make sure that the lines exit the radio underneath the power cables.

Terminate your new lines as you prefer. I like to use a DE-9 connector.

Lastly, keep in mind when connecting to the microphone that the radio has an internal preamplifier, so keep your audio level on the microphone line low.

The author can be contacted at: yokshs [ at ] gmail [ dot ] com.

Last Updated January 15, 2012
©1997-2012 Kyle Yoksh
Posted to Repeater-Builder January 26, 2012