9 ELECTRONIC COMMUNICATIONS-SYSTEMS COMPRISING TRANSMITTERS, RECEIVERS, MODULATORS, DE-MODULATORS, CONTROL PANELS, INTERFACE PANELS, SIGNAL AND DATA PROCESSORS, RECORDERS, SIMULATORS, ANTENNAS, TRANSMISSION LINE ELEMENTS AND PARTS, REPLACEMENT PARTS, AND SUBASSEMBLIES THEREFOR, AND SIGNAL SIMULATORS AND SIGNAL MEASUREMENT APPARATUS FOR SAID SYSTEMS