Can you hear me now?

A project log for PMC-35V - an Open-Source Mobile VHF Radio

An attempt at making a mobile radio that's hackable, moddable, and easy to build.

Patrick McDonnellPatrick McDonnell 05/28/2015 at 13:450 Comments

Connectors, connectors, standards and pinouts, and no two companies can agree on one.

I want the radio to be able to use a wide variety of microphones to keep with the easy-to-use theme, but it seems there are as many microphone connectors and types as there are radios. Even within a manufacturer's own product line 2, 3, or 4 different microphone styles are used.

Enter the solution: RJ45, or it's common name, the ethernet plug.

Yep, that guy. From browsing around forums and reference sites it seems the venerable RJ45 plug is one of the more common types of plugs for mobile radio microphones. But of course, we can't expect companies to agree on one standard pinout for it though, right? Yes, it seems each microphone from each company uses its own special pinout.

For the early development of this project, I've settled on using the microphone pinout used in several kenwood radios, which goes as follows.

This pinout is used in the microphone handsets with the keypad on them, as seen above. However while you would think you could enter frequencies with that keypad, it's actually only used for dialing DTMF codes (the phone beeps).

I really wanted to use another pinout from Kenwood, this time the connection for the TM-271A which allows for full utilization of the keypad for setting frequency, channel, and all kinds of goodies. Here's that pinout.

The devil is in the details. You can see above that Pin 8 is used for keypad serial data, however there's no documentation as to what kind of communication there is between the microphone and the radio itself. I don't have one of these microphones, or a logic analyzer for that matter, so unless there's more information out there about this serial line it looks like entering frequencies will have to be done by hand.

That's all for now. Stay tuned!