Icom IC-746, Часто задаваемые вопросы

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IC-746 FAQ
ohms impendence, and the impedance mismatch will exacerbate the signal level deficiencies.
Some microphones operate at much higher impedances (as high as 100K) and, unmatched,
will suffer from distortion in addition to signal level problems.
Since you're already wiring up a new mic cable, you might want to short pins 6 and 7 with
the chassis ground to assure that they are at the same ground potential. This often helps
reduce RFI from coming in through the mic cable.
3.3.3 Can I use a Heil microphone with the IC-746?
Yes, most Heil microphones work well with the IC-746. Bob does this himself.
As with any dynamic microphone, be sure you have a DC blocking capacitor in the circuit to
isolate the mic element from the DC supply voltage Heil's pre-wired mic harnesses are
perfect for this.
A notable exception is the HS-706 which (as the sales literature clearly states) ONLY works
on the IC-706 series.
3.3.4 How do I adjust the IC-746 for a Heil headset?
In theory, the IC-746 has enough microphone gain to use an unaided Heil microphone. Heil's
May, 2000, newsletter discusses this topic, see:
http://www.heilsound.com/newslettermay00.htm
In short, you use moderate mic gain (50-75%, 12-3 o'clock position) along with moderate
compression (8-10db, 12-1 o'clock position) for the best results.
3.3.5 Do I need a pre-amp to use a Heil microphone?
While the above procedure works for most rigs, it does not seem to work for everyone. For
the few that still have gain problems, adding the Heil HMP microphone pre-amp should
work.
Some speculate that the differing mic gain requirements are due to different versions of the
IC-746, or simply due to widely varying component tolerances. Nobody has collected
enough information yet to nail this issue down.
DO NOT use the HMP pre-amp unless you're sure you need it. Too much gain will distort
your transmitted audio; with all the usual detriments (hard to copy, splatter, etc...)
If you decide you need a pre-amp but want to build it instead of buying it, then check out:
"Build a low cost Boost Microphone"
QST, Aug, 1989
along with the Icom specific mods available (DC blocking capacitor, etc...) from KK5DR
(Matt Erickson) at:
kk5dr@ev1.net
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2003-02-08