by BruXy » Thu Mar 05, 2020 2:01 am
Looks like, they were using some CCTV camera with remote control for zoom, pan, tilt. The schematics has 74HC943, which is 300 Baud modem:
Full duplex low speed modem It provides a 300 baud bidirectional serial interface for data communication over telephone lines and other narrow bandwidth channels It is Bell 103 compatible The 74VHC943 utilizes advanced silicon-gate CMOS technology Switched capacitor techniques are used to perform analog signal processing MODULATOR SECTION The modulator contains a frequency synthesizer and a sine wave synthesizer It produces a phase coherent frequency shift keyed (FSK) output LINE DRIVER AND HYBRID SECTION The line driver and hybrid are designed to facilitate connection a 600X phone line They can perform two to four wire conversion and drive the line at a maximum of b9 dBm DEMODULATOR SECTION The demodulator incorporates anti-aliasing filters a receive filter limiter discriminator and carrier detect circuit The nine-pole receive filter provides dB of transmitted tone rejection The discriminator is fully balanced for stable operation.