Background:
Two-way radio communication relies on the modulation content contained
within the signal. Maintaining a high modulation level is crucial in
providing the highest possible efficiency from any transmitter
operating on AM, FM, and SSB. Current two-way radios normally rely on
microphones that inherently change audio levels delivered to the
transmitter. This causes transmitter modulation to fluctuate greatly
depending on voice level and pitch. This audio fluctuation lowers the
average modulation* levels applied to the transmitter, resulting in
less than optimal transmission range.
*Average modulation levels for voice type transmissions are
approximately 35-45%

General Product Description:
An electronic module that can be fitted to two-way radios that
provides dynamic speech compression and limiting on transmit. The
speech compression will provide a constant level (95-100%) of
modulation to transmitted signals. The module will also incorporate a
"noise gate" that will effectively eliminate background noise below a
desired level.

http://www.telstar-electronics.com/d...evelopment.htm