. Il giornale tecnico Bell System . il filtro quency ha una lunghezza compresa tra 40.2 mm e 41.8 mm e quelli del filtro ad alta frequenza tra 23.8 e 24.3 mm. Lo spessore dei cristalli in tutti e quattro i filtri a frequenza più bassa è di 0.63 mi-limetri, nei successivi quattro filtri di 0.82 millimetri, e nei filtri ad alta frequenza di 1.1 millimetri. L'uniformità di spessore è principale per quanto possibile in quanto contribuisce all'economia nella realizzazione DEL cristallo DEL sistema A CAMPANA manu- 130 TECHNICAL JOURNAL. Nell'intervallo utilizzando la stessa cristallinità l'impedenza e f
1341 x 1864 px | 22,7 x 31,6 cm | 8,9 x 12,4 inches | 150dpi
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. The Bell System technical journal . quency filter rangefrom 40.2 millimeters to 41.8 millimeters in length and those in thehighest frequency filter from 23.8 to 24.3 millimeters. The thicknessof the crystals in all four of the lowest frequency filters are 0.63 mi-limeters, in the next four filters 0.82 millimeters, and in the highestfrequency filters 1.1 millimeters. Uniformity in thickness is main-tained as far as practicable since it contributes to economy in manu- 130 BELL SYSTEM TECHNICAL JOURNAL facture of the crystal. Within the range using the same crystalthickness the impedance and frequency differences, called for by thedesign of the different filters, can be provided by variations in widthand length of the crystals. The ratio of width of the crystals to theirlength ranges from about 1/2 to 4/5. The major surfaces of the crystals are plated with a thin layer ofaluminum deposited by an evaporation process. This plating isdivided along the center line lengthwise of the crystals to form the two ELECTRICAL AXIS = X. MECHANICAL AXIS=Y OPTICAL AXIS = Z Fig. 6—The crystal elements are out with their major surfaces perpendicular tothe electrical axis of the natural quartz, with their side surfaces making a small anglewith the mechanical axis, and with their end surfaces making a small angle with theoptical axis. electrically independent crystals. Since the crystals vibrate longi-tudinally with a node across the middle, they are clamped at this nodein mounting. Figure 6 shows the orientation of the crystal plateswith respect to the natural axes of the quartz from which they are cut.The plates are cut as accurately as is practicable to the dimensionscomputed making a small allowance in length and then the crystal isfinally adjusted in an electric circuit by grinding the end of the crystaluntil the resonant frequency falls within five or ten cycles of thatdesired. CRYSTAL CHANNEL FILTERS 131 Considering again the filter schematic as a whole (Fig 3) andneglecting t
