Good Audio
I always get compliments about my audio quality.
Several people have asked how I achieve it. Here, I give away my secrets.
There is no magic involved, it is mostly due to using good quality components in the
audio chain, and bypassing all of the built-in audio processing.
Virtually all modern amateur radios have audio filtering and various other levels of processing
to give maximum "communications efficency". That probably does help at least a little with weak,
noisy signals, but for more normal use it really isn't required. There are also rumors, which may or may not
have a kernel of truth, that Japanese radios tend to have the audio processing biased for Japanese
voices/language (not sure I really think there is a significant difference, but the rumor is out there).
I have used the following successfully with two radios, an IC-7000 and an IC-7600.
Microphone
The start of the audio chain is a good microphone.
I use a Heil PR40, but almost any good quality microphone will work well.
To support it, I use a boom mount clamped to the desk with a vibraton damping mount
to actually hold the PR40. Again, cheaper alternatives will work just as well provided
that you take care to somehow insulate the microphone from vibration from (for example)
fans in various equipment, as well as picking up noise from your touching the desk, putting
down a pen on it, etc.
Audio Pre-Amplifier
A pre-amp is needed for the microphone.
I use the EQ-Plus from W2IHY. Julius has done a first class job with this (same is true of all
of his products), it really allows you to tailor your audio exactly as you want it, but in addition
it had features such as the "downwards expander" which attenuates quieter sounds. The effect is much
nicer than a noise gate, which just chops off sound below a certain threshold. Downwards expansion
is a progressive attenuation. It sounds much smoother. But, unless you have a particularly noisy
shack, a noise gate would probably work fine. The result of both is that when you are not speaking,
there is no sound, no background noises.
Connecting It Up
The output of the pre-amp is going to be nice clean audio.
What we don't want to do is apply this to the mic input, and allow the tranceiver audio circuitry to
"shape" it.
Most amateur radios have some form of auxiliary connector(s). This is taken from the manual for the IC-7600:
Pin 4 connects directly to the modulator (i.e. it bypasss all of the normal microphone circuitry).
That is where we apply our nice clean audio.
While we are here, we also need to think about a PTT switch. The one on the hand mic is not really
an option. Although the manual is not entirely clear, unless you read what it says a few times, pin 3
is PTT. Ground it, and the transceiver goes into TX.