MANUFACTURE OF QUARTZ CRYSTAL FILTERS 531 



tion of about 0.25 db over a band 3 KC wide. The peak losses are 

 from 75 to 90 db, with the intervening "valleys" approximately 65 db. 

 The other curves illustrate three types of defects occasionally ob- 

 served, namely: {a) displacement of one attenuation peak caused by 



TWINNING IN 

 QUARTZ PLATE 



FREQUENCY 



Fig. 14 — Insertion loss characteristics of crystal channel filters, showing the effects 

 of deviations from normal conditions. 



twinning in one of the crystal plates, (&) abnormal distortion caused by 

 a 0.1 per cent error in resonance adjustment, and (c) low loss at peaks 

 caused by leakage across a crystal or by components which are in- 

 adequately balanced to ground. As an aid to locating the particular 

 components or adjustments which are responsible for such defects, a 

 catalogue of "trouble-shooting" instructions, arranged by classes of 

 filters and types of symptoms, has been compiled. 



Cleaning, finishing and labelling constitute the remaining operations 

 on crystal filters. High temperature processes such as vapor degreas- 

 ing and baking of the finish are inapplicable here because of the nature 

 of the component apparatus in the filter. The surface is scratch- 

 brushed, washed with a solvent and sprayed with aluminum lacquer. 

 Rubber stamps and printers' ink are then used to apply the terminal 

 and type designations. 



Conclusion 



Crystal filters exemplify the trend toward higher frequencies and 

 higher precision in modern carrier systems. These advances in design 

 have required the development of new manufacturing processes and 

 refined methods of adjusting and testing, and demand increased care 



