A new measuring set for message circuit noise

A new message circuit noise measuring set is described. The instrument is an easily portable, visual-indicating and direct-reading device with which rapid and accurate noise measurements may be made. The set is fully transistorized and battery powered, small in size and light in weight. It can be used for bridging, terminating and noise-to-ground measurements with a variety of plug-in weighting networks, one of which is the new C-message weighting designed for the 500-type telephone set. The sensitivity of the set is such that it can detect −90 dbm. This value is chosen as the new reference for measurement and is defined as “zero dbrn.”