706: Microphone Tips

© 2003-2011 by Harold Melton, KV5R. All Rights Reserved. Rev.06/11/05

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Micorphones and the Icom 706MkIIG

If you really want to connect another mic:

The 706 uses an 8-pin “modular” RJ connector for the microphone. This is the same as used by CAT-5 computer LAN (network) cables. The connector costs $4+ each and requires a rather expensive assembly/crimp tool. My way is, of course, much better.

  1. Go to office/computer supply store.
  2. Buy a nice soft CAT-5a LAN patch cable, one with nice molded strain relief plugs. Get a 10-footer.
  3. Cut off one end, or cut in half to make two mic cables.
  4. Ring out and document pin numbers to wire colors.
  5. Solder the conductors into your mic or other audio accessory.


You can find an old, classic mike and replace the element in it with a modern electret condenser. (See photo) ElectroVoice Mercury and Shure Unisphere A. The Shure has been modified with a dual-element electret, PTT switch, and CAT-5a cable.. I don’t use it because the sound quality is inferior to the stock mic…


  1. The supplied HM-103 hand mike is the best one you can run on the 706. I do NOT recommend using other mikes on the 706, except the Heil iCM series. Other mikes, including Icom desk mikes, will have a sound clarity that is inferior to the stock hand mike (yes, really)… The HM-103 sounds best when you talk across it. Never place it flat against the mouth as this will cause considerable distortion.
  2. Rewire the mic’s on-off switch for PTT.
  3. Wire the element always “hot” or you won’t be able to use VOX.
  4. On the other hand, a mic off switch is useful when running SSTV where you need to talk then transmit SSTV.
  5. Obtain a quality electret condenser mic assembly, designed for 8 volts DC phantom power. A setreo mike element, used on cam-corders, may be wired in parallel, and you’ll get lots of output that’s needed by the “pre-Pro” Icom radios. These will not sound as good as the stock hand mike.
  6. Bob Heil will not sell you a bare iCM element, even if you beg!


4 thoughts on “706: Microphone Tips
  1. can you or should you use both a FL103 narrow SSB filter along with a
    fL223 wide band filter together in the Icom 706MKII
    g? will it work well or should i not??

  2. I found your 706 site very interesting. I’m sure you are very busy but hope you could help me with connecting a Kenwood MC60A mike to a IC7000 radio.

    Thank you, George KF5NAJ

    • Easiest and safest way is to buy an adapter pigtail (Heil, MFJ, etc). That way you don’t mod your mic, and don’t need an RJ45 modular crimper.
      If you decide the hard way, you need the schematic for the mic, and for the radio’s mic jack, and an RJ45 crimper — then you end up with a MC60A dedicated to the one radio, and an RJ45 with no rubber strain-relief.
      I’d just buy the pigtail, get one with a nice strain-relief on the RJ45, and not mod your mic.
      73, –kv5r

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