This cable can be used in both Maxtrac and Radius radios in order to link two of them together as a repeater. I will not go into repeater operation theory or duplexers, etc. You should already know this stuff if you are building a repeater.
An ideal application of this circuit would be a cross-band range extending repeater for portable use.
All of the circuitry involved can be built into a double ended female RJ-45 connector. Just make sure you label it as such...
This design was originally printed in the trade publication Mobile Radio Technology.
Take a look here for the schematic of the circuit you will need to build.
There are a couple of modifications that need to be made to the radio in order for this to work.
Build 2 very short 8 conductor patch cables to go between each radio and the modified RJ-45 coupler. Keep the leads short to aviod stray RF pickup. Also, build the cables identical so that no matter how you hook it up, you can't get the polarity wrong.
Once the audio modification has been done, set up the radios for testing and adjust the deviation as necessary to get a receive deviation of 3kHz to produce a transmit deviation of 3kHz.
One minor drawback is in the nature of the PTT circuit. If for some reason, one of the radios fails or loses power, the adjacent radio will key up. Therefore, you should set the time-out-timer of both radios to 3 minutes to prevent transmitting a dead carrier as well as meltdown.
Below is an updated article of the above information with a couple of minor changes. Notably, this should correct the meltdown problem mentioned above if a radio fails. Also, this will allow you to use PL/DPL squelch, and it is simpler to build. The article is from the trade magazine Mobile Radio Technology.
Click the links to see page 1, page 2, and page 3. If you want to download a zip file of all three pages, click here.
You can also see the updated modifications done on a 5 pin logic board of a Maxtrac 50 before as well as after. This is an "A" radio.