Use Kenwood MC-45 mic on your Icom 706.
by Kyle Yoksh, K0KN
September 30, 2005

This adds DTMF capability to your 706 for low cost. Audio reports on FM and SSB have been very good with this mic.

First, you will need a new coiled mic cord. Kenwood uses a common GND for the PTT and 8v supply, as well as the MIC ground, so the stock mic cord is just 4 conductor.. Icom uses a separate MIC ground, so it is necessary to use a coiled cord with 5 conductors. I found a coiled cord in my junk box with RJ45 modular connectors already on it! These were sometimes used for old wired-in cellular car phones.

Prepare the mic end of the cable with a suitable strain relief, or in my case a simple knot. Note that a little physical modification of the mic case will be needed if you select the latter method.

With the new cable ready, start by finding the GND side of the mic element with an ohmmeter. Measure between pins 4 or 5 of the original mic connector (GND) and both mic element connections. When you find the ground side of the mic, cut this wire close to the PCB. Bend the wire away from the PCB a safe distance. Make sure you have enough room to attach a new wire to the mic element. You've now isolated mic ground from common ground. You will attach a wire to the mic element in just a moment.

Apply a drop of glue to secure the mic element to the PCB, as the wire you just cut also used to support the mic element. Connect your new RJ45 cable to the mic using the table below. For those new to RJ45 connectors, hold the connector with the pins facing up, the locking pin down, and the cable towards you. The pin numbers are 1 through 8, left to right.

Original pin #                      RJ45 Pin #
1                                            6
2                                            4
3                                            1 
4, 5                                         7
Mic Element GND (now isolated)               5  
You may find that the DTMF level is adjusted too low for reliable detection, as I did. A small potentiometer is located on the bottom of the PCB. Carefully remove the screw holding down the PTT switch and remove the PCB. Adjust the pot until the DTMF audio is about the same volume as your regular spoken voice, or just a little softer. This should work fine.

mc-45.gif - 13090 bytes

The schematic for the MC-45 shows that the current drain of the MC-45 is less than 200mA at 8.5 VDC. Looking at the IC-706 specs, I noticed that the max draw from the 8V mic connector is 10mA! To be safe, I connected +8v to my MC-45 and attached an ammeter. I could not find any way to make my MC-45 draw more than 8mA.

Note that the schematic shows the mic connector from a Kenwood radio's point of view. In other words, the pin locations shown will be backwards of your mic.

The MC-45's connector has pin numbers on it, make sure to observe these pin numbers when rewiring your mic.

It's also not a bad idea to double check all connections with an ohmmeter before connecting the mic to your rig.


Please email me with your results also!

73 and good luck!

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Last Updated January 2, 2012
©1997-2007 Kyle Yoksh