N-1 CARRIER TELEPHONE SYSTEM 



423 



The carrier frequency transformers also exemplify small size. They are 

 alike in structure, employing acetate filled windings assembled over small 

 toroidal molybdenum permalloy dust cores which are broken in half to 

 accept the winding assembly and cemented together again. The winding 

 and core assembly is supported from the terminals which are molded into 

 the cover plate. This construction method further simpUfies fabrication by 

 eliminating the need of intermediate lead wires from the winding assembly, 

 the fine wire of the windings being connected directly to the transformer 

 terminals. 



All transformers are housed in drawn aluminum cases and are equipped 

 with threaded metal inserts in the covers for mounting. Construction fea- 

 tures of the various transformers are shown in Fig. 3. 



Fig. 4 — Quartz crystal units used for carrier frequency oscillator control. 



Crystals 



The 12-channel carrier frequencies required for the system are supphed 

 by quartz-crystal controlled oscillators covering the range of 168 kc to 

 256 kc in 8 kc steps. These crystals are -1-5° X cut quartz plates operated 

 in a fundamental extensional mode, with gold electrodes plated on the 

 major surfaces, wire mounted and hermetically sealed in metal holders with 

 mounting leads. The crystal used to control the 304 kc carrier supply oscil- 

 lator for the group modulator is a DT quartz crystal plate operating in the 

 shear mode, otherwise similar to the crystals for the channel frequencies. 

 The two designs are shown in Fig. 4. 



Varistors 



Nearly eight hundred small germanium varistors are used as circuit ele- 

 ments in the two terminals of an N-1 system. Slightly more than half of this 



