Electronic measurement apparatus; namely, integrated Services Digital Network ISDN network termination tester; ISDN signal balance ratio bridges; ISDN impedance bridges; computer software for use in D-channel monitors; monitors for International Telegraph and Telephone Consultative Committee CCITT signaling systems; level generators; digital level meters; line patch/intercoms; speech attachments and two-wire switch-overs; AF audio frequency sweep measuring setups for various frequency ranges; level measuring sets for frequency ranges; selective level meters; balancing attachments; audio analyzers; universal networks and filters; noise generators for acoustic medical control system and telecommunications measurements; storage display units with digital image storage for use with selective level meters; transmission system analyzers; T.V. pilot level meters; milliwatt power meters; test point selectors for various frequency ranges; white noise measuring devices for noise and Noise Power Ratio NPR measurements; filter and converter plug-in units, fiber optics sources comprising light emitting diodes LED and lasers for feeding optical devices for test purposes; optical power level meters; optical attenuators; fiber optics test kits comprised of optical sources, optical attenuators, optical power level meters for LAN local area network and telecommunications applications; fiber optics test adapters and cables; spectrum and network analyzers; computer software for use in measuring crystal equivalent circuit parameters; computer software for use in control and evaluation of System Network Architecture SNA equipment; radio-link measuring equipment for distortion measurements on radio-link and satellite systems; data circuit test sets for measuring impulsive noise and interruptions; data line analyzers - telephone channel simulators; data network diagnostics equipment for CCITT data communications interface standards V.24, V.35, X.20/X.21 and Electronic Industries Association EIA RS-232 computer interfaces; analog switching units; rack cabinets - computer software for use in network management; data performance analyzers; data analyzers; interface converters; teletext testers; data testers; modem testers; interface testers; Voice Frequency Pulse Code Modulation PCM testers; signaling testers; PCM channel measuring units for measurements on PCM coders/decoders between analog and digital interfaces; test point scanners; PCM channel generators; error ratio measuring sets for measuring bit, block, and code error ratios on data channels; digital error detectors; jitter generators; jitter meters, analyzers for comprehensive testing of network elements and digital transmission systems; jitter modulators; regenerator measuring devices for measuring noise immunity of regenerators; cable simulators; frame analyzers; AC alternating current power line harmonic analyzers; AC voltage stabilizers; measurement subsystems comprised of level meters, transmission system analyzers, and remote access switches for automatic measurements on Frequency Division Multiplexing FDM systems; integrated measurement and surveillance systems comprised of measurement subsystems for network configuration and remote measurements on FDM systems and for centralized monitoring and measurements on FDM systems; satellite test systems comprised of a radio-link measuring setup, transmission systems analyzer, and white noise generator for semi-automatic line-up of satellite links; digital multiplexer test systems comprised of an error measuring unit, a filter generator, a filter meter, a spectrum and network analyzer, a return loss bridge, a frequency counter, a digital storage oscilloscope, and a control computer; automatic test systems comprised of a channel test set and a test point scanner for testing PCM circuit modules and systems; automatic monitoring systems comprised of a mainframe, an alarm collecting unit, and a multiplex analyzer for digital communications cable measuring systems comprised of a selective level test unit, a level generator, a data logger, and a test point scanner for automatic monitoring of undersea FDM cable systems; functional test systems comprised of a channel measuring unit, an analog, digital and pattern generator, and a test interface for conventional telecommunications applications; functional test systems comprised of a channel measuring unit, analog mainframe, test interface, mainframe and digital oscilloscope for testing ISDN applications; VERSA Module Europa bus VMEbus extensions; universal test interfaces for performing measurements on communications equipment; systems racks to accommodate measuring equipment; cables, change-over switches, coaxial chokes, DC direct current loop holding circuits, cable connectors, adapters, attenuators, terminations, standard mismatches, z-matching pads; equipment cases, storage containers and dust covers for the foregoing