Audio signals as music or speech have big dynamic ranges. There are silent and loud sections. These audio signals aren't too good for a transmitter, which requires audio signal with constant level on the input. Limiter is a device, which weakens loud signals and intensifies silent signals.

On its output there is signal with constant level. Signal clipping on the limiter output allows to increase the signal level without exceeding maximum frequency deviation limit 75 kHz. It's very suitable since preemphasis is used.

The limiter circuitry features built in pre emphasis that can be set at 50uS, 75uS or None. In the USA the setting should be 75uS and for the rest of the world the setting should be 50uS.

The limiter compressor circuit operates the audio gain around a fast attacking limiter in conjunction with a gentle AGC. The limiter circuitry also includes selectable pre-emphasis.

If your transmission chain does not include any similar device, you should build this one. You will be surprised by its quality, efficiency and simplicity. This is Compressor/Limiter/Clipper.