OPTICAL FIBER SIGNAL TRANSMISSION MACHINE; OPTICAL FIBER SIGNAL REGENERATOR; OPTICAL FIBER SIGNAL RECEIVER; OPTICAL FIBER COMMUNICATION MACHINE, NAMELY, SYNCHRONOUS DIGITAL HIERARCHY ADD/DROP MULTIPLEXER, OPTICAL MODEM FOR USE WITH OPTICAL FIBER, OPTICAL SIGNAL REPEATER; COAXIAL CABLE SIGNAL CARRIER; SIGNAL RECEIVER; PULSE CODE MODULATION SIGNAL CARRIER, NAMELY TL/EL LEASE LINE EQUIPMENT, NAMELY, MULTIPLEXERS AND MODEMS; SIGNAL INTENSIFIER; SOUND AMPLIFIER; RADIO TRANSMITTER; ELECTRONIC SWITC...