Radio/Intercom Interface Info
Here is the wiring diagram for the Kenwood TM-271A to Flightcom 403mc
Resistors R2,3&4 and the capacitor match the mic power circuit in the Kenwood factory mic and is needed due to the fact that the 403mc connects the mic directly to the radio and relies on the radio to power the mic. Switch 1A/B is a DPDT toggle that selects either the intercom mic or the factory radio mic. Switch 2 selects an external speaker or sending the radio speaker signal to the intercom. The "Radio Plug is a standard RJ-45 Ethernet plug to plug into the front of the radio and the "MIC" connections are a RJ-45 jack to plug the factory Kenwood mic into. The "Radio SPKR" plug is a standard mono 1/8 headphone style plug. the Tip/Ring/Sleeve and Tip/Ring connections are to the intercom.
I have also made a couple of interfaces for the Flightcom IIsx portable intercoms to connect to the TM-271A...
The wiring diagram for these is quite similar and will work for most portable intercoms:
If the transmitted audio is too loud you may need R4 and experiment with it's value and possibly with the value of R3 of not for the IIsx. The diagram is much the same as the one above so refer to the above notes.
Thanks to Guy Howard for the initial info to get me going on this. Don't forget to do his "Scream Test" on your system to see if it can handle high volume levels found in a speeder without distortion......
Any questions, e-mail us at: firstname.lastname@example.org