The COMTEST SYSTEMS, Inc. Model 3100 is a compact, microprocessor controlled Service Monitor for testing FM, AM, and SSB transceivers. Its microprocessor provides it with extreme versatility and user friendliness. Its low weight and optional D.C. powered version permit convenient field use, from either internal battery or external 12 VDC sources. The Model 3100 will generate and receive from 400 KHz to 1000 MHz in 100 Hz steps, but with a usable range from 100 KHz. Internal modulation sources provide a variety of choices covering most industry standard coded squelch formats. The generator output is continuously variable from 0.03 uVRMS to 316 mVRMS. An internal CRT display shows modulation waveforms or a spectrum analyzer display, and may also be used as an oscilloscope. A meter reads Modulation, A.C. RMS volts, SINAD, or R.F. power. In receive mode, the LCD display shows carrier frequency error, modulation frequency and decoded sub tones or digital coded squelch.