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BELL SYSTEM TECHNICAL JOURNAL 



crystals could be used to control oscillators and that much more stable 

 oscillators could be obtained in this fashion. These were later applied to 

 controlling the frequency of broadcasting stations and radio transmitters in 

 general and about 1925 Mr. W. A. Marrison appHed them to obtain a very 

 constant frequency and time standard, which is now used considerably by 

 the Bell System, by radio broadcasting systems, and by power companies. 

 The oscillators were subsequently improved by using crystals with small 

 temperature coefficients as described in Section V. At the present time 



BLOCKING CONDENSER 



_J 



DISTRIBUTED 



CAPACITY 



OF COIL 



3 1 



Fig. 1.3 — Nicolson's oscillator circuit 



crystal controlled oscillators are used very widely in radio military and 

 commercial applications. 



Another large use for quartz crystals is their use in providing very selective 

 filters. Probably the first use of a crystal to select a narrow frequency 

 range was made by Cady.^ Using the very sharp maximum in current 

 through a crystal at its resonant frequency, Cady proposed the use of such a 

 crystal as a wave standard. This is equivalent to the use of a crystal 

 as a tuned circuit. By incorporating a crystal in a three-winding trans- 

 former and balancing out the static capacity of the crystal by an auxiliary 

 condenser, W. A. Marrison^ improved the selecting ability of a crystal used 



6 Patent 1,994,658, filed June 7, 1927, issued March 19, 1935. 



