Abstracts of Technical Articles by Bell System Authors 



Crossbar Toll Switching System} L. G. Abraham, A. J. Busch, and 

 F. F. Shipley. A new crossbar toll switching system was placed in service 

 in Philadelphia in August 1943. Important improvements offered by this 

 system include: 



1. Transmission objectives are met more readily and substantial econo- 

 mies are obtained in outside plant and in repeater equipment. 



2. Extended use of toll dialing results in operating economies and im- 

 proved service to subscribers. Calls over circuits still on a ringdown basis 

 are also handled more expeditiously and with operating economies. 



3. Flexibility due to the use of sender and markers to control establishing 

 connections will be useful in meeting future toll switching requirements. 



Low-Frequency Quartz-Crystal Cuts having Low Temperature Coefficients? 

 W. P. Mason and R. A. Sykes. This paper discusses low-frequency, low- 

 temperature-coefficient crystals which are suitable for use in filters and 

 oscillators in the frequency range from 4 to 100 kilocycles. Two new cuts, 

 the MT and NT, are described. These are related to the +5-degree X-cut 

 crystal, which is the quartz crystal having the lowest temperature coefficient 

 for any orientation of a bar cut from the natural crystal. When the width 

 of the +5-degree A^-cut crystal approaches in value the length, the motion 

 has a shear component, and this introduces a negative temperature coefficient 

 which causes the temperature coefficient of the crystal to become increas- 

 ingly negative as the ratio of width to length increases. 



The MT crystal has its length along nearly the same axis as the -j-S-degree 

 X-cut crystal, but its major surface is rotated by 35 to 50 degrees around the 

 length axis. This results in giving the shear component a zero or positive 

 temperature coefficient and results in a crystal with a uniformly low tempera- 

 ture coefficient independent of the width-length ratio. A slightly higher 

 rotation about the length axis results in a crystal which has a low-tempera- 

 ture coefficient when vibrating in flexure and this crystal has been called the 

 NT crystal. The NT crystal can be used in a frequency range from 4 to 50 

 kilocycles, while the MT is useful from 50 kilocycles to 500 kilocycles. 



A special oscillator circuit is described which can drive a high-impedance 

 NT flexure crystal. This circuit, together with the NT crystal, has been 

 used to control the mean frequency of the Western Electric frequency- 

 modulated radio transmitter. 



^Elec. Engg., Transactions Section, June, 1944, 

 ^Proc.LR. £., April 1944. 



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