The LM383 is an audio-power amplifier that is capable of producing up to 8 W of audio output. R1 is essentially a load resistor for the hand-held transceiver's audio output. R2 can be composed of two fixed resistors in a 10:1 divider arrangement, but using a potentiometer makes it easy to set the amplifier's maximum gain. When powered from a vehicle's electrical system, the amplifier's +12V power source requires filter L1 to eliminate alternator whine. The LM383 can be mounted directly on the heatsink because the mounting tab is at ground potential.