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BELL SYSTEM TECHNICAL JOURNAL 



standard F-cut of the same frequency and area. These curves not 

 only illustrate the reduction in temperature coefficient but also show- 

 that in the A T-cut plate the secondary frequency spectrum has been 

 eliminated over the temperature range of the test. This is to be 

 expected, for 35° is close to the 31° zero coupling point; hence such 

 coupling as does exist is small in magnitude. 



y -20 



■-80 



-90 -75 -60 -45 -30 -15 15 30 45 60 75 90 



ANGLE OF ROTATION ABOUT X AXIS IN DEGREES (6) 



Fig. 4 — Temperature coefficient of frequency of the vibration depending upon Cee' as a 

 function of rotation about the X axis. 



These ^r-cut plates can be produced with a sufficiently low temper- 

 ature coefficient so that for most applications the temperature regu- 

 lating system can be discarded, and in addition a simplification of the 

 secondary frequency spectrum is obtained. Furthermore, the ad- 

 vantages of the F-cut plate, i.e., clamping and activity, have not 

 been sacrificed. 



Additional tests on .4 T-cut plates indicate that it will be possible to 

 use them to control reasonable amounts of power without danger of 

 fracture. At 2 megacycles, 50-watt crystal oscillators would appear 

 to be practical and in some experimental circuits the power output 

 has been run up to 200 watts without fracturing the crystal. The 



