A Review of the Heil HS-706 Boom Microphone
While I have generally been pleased with the Icom 706 MKII that I bought
years ago, there's no doubt that is has a few puzzling "features."
One that has 
been
noted by many owners, especially of earlier models, is a rather low audio
gain level with the stock microphone. Getting the ALC to cut in without
running compression was difficult with the stock mike. About 2 years ago
I purchased the Icom TTP mike because I wanted to be able to access repeater
features. I had hoped for a possible increase in levels with the mike,
but found them to be essentially the same as the stock mike included with
the rig.
Not that these mikes didn't have good audio, but that varied with the mode of modulation. I got good audio comments with SSB, but not as much with FM. I have run both the Icom and a Kenwood dual band rig in the car, and universally the Kenwood was thought to sound crisper and louder on VHF FM by other hams.
Heil Sound has come out with two microphones especially designed to work with the 706. The advertisements stress that these microphones have higher output elements that would drive the 706 with sufficient audio. I decided to buy the boom microphone, which was configured with one earpiece suitable for mobile operations.
The output of this microphone, and the tone quality, lives up to the
claims by Heil. I'm able to run the microphone without the compressor
and still get perfect levels at half scale on SSB. To run with the compressor,
you must actually set the level down to a 1 or 2 on the scale of 10. On
FM, one must be careful to set the levels by getting a ham with a good
ear to give you feedback, or you may 
over-deviate.
When running both rigs in the car, the Icom now sounds crisper to most
listeners.
However, I can't say I'm completely satisfied with the mike. The cable is short, so much so that there's just enough cable to go from the remotely mounted head, mounted center dash, to my head, with routing around the shifter and enough slack to operate the PTT with my left hand. If I had the radio mounted anywhere further away (true for most installations) I'd have to build a shielded extension cable. There is also something irksome about head adjustment bands that are too loose. There's no chance they will stay adjusted. However, considering the vast audio improvements, these quirks are worth putting up with.
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