measuring, monitoring, analyzing and recording devices, installations and automatic systems for electronic and optical, digital and analog data and communication transmission; namely, noise meters, linear distortion meters, reflection coefficient meters, phase meters, group delay meters, communication equalizers, communication filters, line simulators, non-linear distortion measuring instruments, spectrum and network analyzers, low frequency analyzers, data- and protocol-analyzers, scanners, test point switches, monitors, stabilized power supplies for A.C. and D.C., bit error measurers, pattern generators, AC line adaptors; AC voltage stabilizers; A.C. power line harmonic analyzers; optical adaptors; attenuators; band limitation filters, band pass filters, band selection filters, bandstop filters, and branching filters; cable connectors and simulators; Butterworth, Cauer and Chebishev filters; coaxial chokes; current loop interfaces; data testers; DC loop holding circuits; digital probes; electrical, electronic and optical displays; DS-1 analyzers; error detectors; frame analyzers; high pass filters; interface testers; jitter generators, meters and modulators; level generators; level meters; level expanders; loop-through jitter generators; lowpass filters; measurement bridges; modem testers, network analyzers; optical level meters; PCM codec analyzers; PCM digital signal analyzers and generators; photodiodes; pilot level meters, pilot stop filters; remote access switches; signal shapers; spectrum analyzers; speech generators; T-adaptors; telephone channel simulators; teletex testers; test probes; test sets for digital exchanges; transformers; weighting filters; Z matching pads; universal networks and measuring location switching and electro-acoustic warning devices, including sirens, signalling and electro acoustic notification devices and traffic controllers, fire fighting signallers