domenica 13 aprile 2014

Using ICOM HM-118 Microphone on 706!

I've bought a (fake) ICOM microphone for using with my 706, an ICOM HM-118.The mike was bought on the 'Bay from a Cinese seller, and costs less than 10 euros included shipping! This microphone is not compatible with 706, but is very easy to adapt, only two wires to cut!

Look at the job of Greg AC2MC link The mod is very easy: cut the wires connecting to pin 3 and pin 8 of the RJ-45 plug. DONE. I've opened yhe HM-118, the internal view is below:

Using a multimeter I verify which wire connects to which pin of RJ-45. In my microphone, the pin 3 is yat disconnected (there is a cut blue wire from curly cable thet is non connected toPCB). If you cut the yellow wire you have finished the job. (WARNING: the color of the wires may vary on different mikes, check the wires before cut anything!).

Instead to using the board circuitry, I decided to apply a mod similar to the HM-36 mod. The circuit of the SE5X mod is this:

For this mod I need to:
  • cut the mic wire on PCB board (in my mike, is the black wire) - circled in RED in the image
  • connect 2k Ohm Resistor and 0.01uF Capacitor in parallel (R//C)
  • connect R//C with black wire coming from curly cable
  • disconnect the red wire on electret capsule
  • connect the other side of the R//C with hot side of the electret capsule
  • connect a 4700 pF capacitor in parallel with the electret capsule

Is easy to see the mod in the following image:

The blue rings os microphone wire are two ferrite beads; between R//C and PCB I put a little strip of self-adesive foam to prevent short-circuits.

Job done! The mike seems to be ok, on-air test and reports in the following days.

PS: Greg AC2MC reports that UP and DOWN stiches are reversed if referred to 706, but in my HM-118 the switches are in the righrt order.

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