An Electret type element provides a high quality, low cost microphone for many
purposes, including some amateur radio transceivers. They might also be
referred to as a "capacitor mike". The element is small, about the size of a
large pea. Radio Shack doesn't sell them anymore but several types are available
from Mouser Electronics (no minimum order). My version had 5" leads, and required
only +2v to +10v supply ( at 1/3 milliamp). The shield on the output cable is
also grounded to the case. It delivers about 140 mv P-P when capacitively
coupled to a high-impedance load. A SWAN-500C has about a 1Meg input, and its
microphone gain can be set at about 50%. With +6v, the electret's output is about
the same as a typical Ceramic type microphone. An Electret's output is quite high
fidelity, essentially flat from 100Hz to 5000Hz. (Cost $3.40 +shpg).
My contention is (at least in theory),that if you offer the full hi-fi range
of audio input to the transceiver, the resulting fidelity being transmitted is
virtually dictated by the response curve of the steep-skirted SSB Crystal Filter.
For example, the SWAN-500C has an SSB filter 2.7 KHz wide. (i.e. 5500.3 KHz to
5503.0 KHz), and their reference crystal oscillator of 5000.0 KHz provides an
ulimate audio range of 300 Hz to 3000 Hz which is quite good for voice communication.
On the other hand, if an SSB filter is only 2.1 KHz wide, you must be very
selective in choosing the reference crystal oscillator....you can decide whether
to utilize that smaller width to emphasize low-freqency audio response, or high-
frequency response, but you can't have both. You could choose 300 to 2400 Hz, OR
1000 to 3100 Hz, for example.