Abstracts of Technical Articles by Bell System Authors (01 January 1941)

Proc. I.R.E., October 1940. Pick-Ups, August 1940. 125 126 BELL SYSTEM TECHNICAL JOURNAL crystal standard (likewise about 5,000 cycles) in a device which produces a rotating magnetic field at the difference frequency. An armature which follows this field controls the tuning condenser of the original electric oscillator, coming to rest when exact synchronism is attained. The small phase vibrations accompanying modulation are not followed because of the inertia of the system. The stability thus obtained for the mean frequency is identically that of a crystal oscillator. Since the actual control is mechanical, no sustaining voltage is required, so that failures in the control system do not result in sudden departures in frequency. 

Mechanical control, moreover, completely relieves the modulating elements of any connection with the stabilization of the mean frequency, so that the modulation range is not restricted. This and other refinements in design permit frequency excursions of hundreds of kilocycles with extremely low distortion. Ultra-Short-Wave Transmission Over a 39-Mile "Optical" Path} ENGLUND, A . B . CRAWFORD, a n d W . W . MUMFORD.