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BELL SYSTEM TECHNICAL JOURNAL 



Greenldge in Chapter XIII of Mr. Heising's book referred to above.^^ The 

 most satisfactory means by far that has been found for mounting crystals of 

 the GT type is that of actually soldering them to thin supporting wires by 

 means of small discs of silver deposited on the crystal at its nodes. This 

 method serves the double role of supporting the crystal and of providing 

 electrical connection to metal electrodes plated on the crystal. Resonators 

 so supported may be made almost immune to mechanical shock and will con- 

 tinue in satisfactory operation through accelerations of several times g. 

 Nearly all crystals which vibrate in a long dimension are now mounted in 

 this way. One manufacturer produced about 10,000,000 crystals of a single 



Fig. 20 — Pressure-mounted GT crystal for sealing in a metal envelope. 



type SD mounted in a three-year period during World War II. Prior to the 

 use of wire supports, such crystals were ''pressure mounted" by means of 

 small metal jaws which clamped from opposite sides at the nodes. A GT 

 crystal mounted in this way is shown in Fig. 20. Crystals so mounted are 

 still in use in the Bell System Frequency Standard, being the first of the GT 

 crystals to go into actual service. This type of mounting is not quite so 

 stable as the wire mounting and is somewhat more difficult to manufacture. 

 One of the wire-mounted crystals such as developed for LORAN and other 

 oscillators of comparable accuracy is shown in Fig. 21. 



The plating of electrodes on the crystal surface has led to increased 

 stability of frequency control, chiefly because the coupling to the electrical 

 circuit may be kept more nearly constant thereby. When separate elec- 

 trodes were employed, the variation in spacing was always found to be a 



