Icom IC-746, Часто задаваемые вопросы

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IC-746 FAQ
3.3 Microphones
3.3.1 What is the best microphone to use with the IC-746?
In theory, your favorite microphone is the best choice, provided you hook it up and adjust it
properly. Its basically just a matter of personal preference.
The confusion lies in the definition of "best". Most users generally agree that the stock hand
mic is generally adequate for general use, but is not "best" or "optimal" for any specific use.
You know the tale; jack of all trades, master of none.
If you want better transmit fidelity (or even broadcast quality sound), then you'll want a full
range microphone, possibly with a dynamic element. Icom's own SM-20 gets good reviews
for this application, as does Heil Goldline microphones. Other microphones will also work;
these just happen to be the most popular.
Many operators have found that the inexpensive studio microphones from Radio Shack work
astonishingly well. Yielding 90% of the performance at 10% of the price makes this a viable,
budget conscious, choice. It also shows just how poor the stock mic is.
If you're after more "punch" for DXing or contesting, then you'll want to look into one of the
Heil DX style microphones. They're frequency responses have been tailored to accentuate
the portions of the voice spectrum that most contribute to understandability. Their great
performance have made them very popular.
For those of you who "want it all", Heil even makes a microphone that switches both ways,
literally. It has two pick-up elements in the same mic, so you can change between
ragchewing and DXing punch at the flick of a switch.
Who says you can't have your cake and eat it too?
3.3.2 Can I hook up a different microphone directly to the IC-746?
Yes, but only if properly wired.
There is more to wiring up an external microphone than just the differing pin-outs. You will
also have to deal with: DC bias, signal level, and impendence.
Icom uses electret elements and incorporate preamps right into their hand mics. The DC
power is fed directly from the rig through the mic cable. If you are using a different electret
microphone, by sure it will operate with the 8 Vdc bias. When using a dynamic microphone,
be sure you have a capacitor (value not critical, around 1.0-4.7 uf) in the circuit to block the
DC supply voltage
Depending upon the microphone, you may have to use a hefty amount of mic gain (and
possibly compression as well) to make up for the lack of the handset pre-amp. You may
even need to use an out-board microphone preamp to get the signal high enough.
Finally, the Icom microphone input is at a relatively high impendence (1-2K ?). A matching
transformer (or preamp) will yield the best results. Most microphones operate at only 600
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2003-02-08