The CL-SIP358, a high-technology FM Stereo Multiplex Transmitter Trainer, is designed to teach and demonstrate the principles of multiplexing two signals on a single RF carrier. The transmitted signal is in the range of 88-108 MHz. The nominal transmitter frequency is 107 MHz. The FM Stereo Multiplex Transmitter is similar in operation to a commercial transmitter, with a pilot tone, (L+R) and (L-R) signals. The Trainer also serves as an FM sweep generator. The reactance (varactor) modulator is provided with either two audio tones (1 kHz and 400 Hz) or an external stereo signal. The composite signal output includes fully adjustable signals of (L+R), (L-R), (L), (R), and a 19 kHz pilot signal.

The center operating frequency of 10.7 MHz is phase-locked loop controlled against a 4 MHz crystal oscillator. The frequency stabilizing circuitry uses binary ripple dividers and phase comparators. The RF frequency is multiplied up to 107 MHz with wide band commercial deviation. The two audio tones (1 kHz and 400 Hz) are also crystal controlled from the same 4 MHz crystal oscillator. When used with an FM receiver, the transmitter's oscillator can be swept at 60 Hz in order to study the detector circuit tuning of the receiver. The FM Stereo Receiver (CL-SIP328) is a companion to the transmitter, or any FM receiver can be used. The transmitter suppresses the 38 kHz signal and transmits a 19 kHz pilot tone. Two frequency synthesizers are incorporated into the system design. The transmitter has a variety of test points which are used by the student to observe the various signals and voltages present throughout the system.