21 ELECTRONIC COMMUNICATIONS EQUIPMENT-NAMELY, REGENERATORS, RADIO-TELEGRAPH KEYERS AND RECORDERS, INSULATORS, RADIO NOISE SUPPRESSORS AND PARTS THEREOF, AMPLIFIERS, ANTENNA COUPLERS, CONVERTERS, TELEGRAPH AND RADIO COMMUNICATIONS RECEIVERS, POWER SUPPLY PACKS, SINGLE FREQUENCY RECEIVERS, TRANSMITTERS, FREQUENCY TRANSMISSION EQUALIZERS, MULTIPLE CHANNEL TELEGRAPH AND RADIO TONE TRANSMITTERS AND RECEIVERS, FIXED AND VARIABLE FREQUENCY OSCILLATORS, LOW FREQUENCY SHIFT KEYERS