Modem with phase coherent frequency modulator - uses filter separation transmitted and received signals and routes received signal to demodulator with carrier detection

摘要

The modulator-demodulator comprises a continuous coherent phase frequency modulator and a filter in the transmission path separating received and transitted signals, a filter and trigger unit and frequency demodulator with carrier detection in the receiver path. Respective interface circuits in both paths comprise a light emitting diode and a photosensitive transistor providing optical coupling and electrical isolation. A transformer couples the modem to a telephone line and the receiver includes a circuit which converts sinusoidal incoming signals into binary voltage signals which are frequency modulated. In addition, incoming signals are routed through the first filter to the filter unit to the receiver path.