PRINCIPLES OF MOUNTING QUARTZ PLATES 



187 



dependent upon the area of the crystal, its frequency and the amount of 

 activity required. One advantage of the clamped type support lies in the 

 fact that many of the unwanted modes of motion are restricted or dampened 

 to the extent that they will not cause serious dips in the activity character- 



CRYSTAL 



B 



Fig. 8.10 — Air gap type mounting. 

 A — Crystal free. 

 B — Crystal clamped at corners. 



L| C, 



fW^ — If— 1 





L, C 



HRP — |f-| 



Co Co 



A B 



Fig. 8.11 — Equivalent circuit of a quartz crystal in an air gap type mounting. 



istic over a wide temperature range. This explains in part the necessity for 

 accurate control of the length and width dimensions for crystals of low radio 

 frequencies using the type of mounting shown in Fig. 8.10A. 



The effect of the airgap on the constants of the crystal equivalent circuit 

 may be determined from Fig. 8.11. In Fig. 8.1 lA is shown the usual crystal 

 equivalent circuit in series with a capacity Ca which represents the capacity 



