. The Bell System technical journal . set of plates by R. M. Jensen. Figure includes aphotograph of the plates used, illustrating the extent of the twinning ineach. All of the plates are —° X-cut plates, having the X X .86 mm. The tabulation below the photograph comparesthe inductance and resonant frequency measured for each of the plateswith the one, designated AN-3, which shows the least effect of there is a good correlation between the amount of twinning in theplates and their change in electrical performances, it is not practical toestimate acc
. The Bell System technical journal . set of plates by R. M. Jensen. Figure includes aphotograph of the plates used, illustrating the extent of the twinning ineach. All of the plates are —° X-cut plates, having the X X .86 mm. The tabulation below the photograph comparesthe inductance and resonant frequency measured for each of the plateswith the one, designated AN-3, which shows the least effect of there is a good correlation between the amount of twinning in theplates and their change in electrical performances, it is not practical toestimate accurately the effect of a given amount of twinning. For thisreason, crystal plates having any twinning should not be used for crystalunits for filters. MANUFACTURING DEVIATIONS IN CRYSTAL UNITS 271 Etching The surface condition of the quartz plates also has some effect on crystalcharacteristics. This surface condition is determined in large part by tlielapping operation used to obtain final dimensions. As described in Chapter. Percentage Increase over Values Measured for AN-3 Plate Resonant Designation Inductance Frequency AN-1 + + .50 AN-2 + + .59 AN-3 0 0 AN-4 + + .04 AN-5 + + .01 AN-6 + + AN-7 + AN-8 + + .37 AN-9 + + AN-10 + + .83 Fig. —Effect of various degrees of twinning on the performance of —° X-cut quartz crystal plates. XIIIi, the plates are given a final lap with 400 or 600-mesh , in turn, is followed by an etching bath which removes foreign short etch, about eight minutes in 47% hydrofluoric acid, has been foundadequate to ensure firm adherence of the metal coating to the quartz. On i The Mounting and Fabrication of Plated Quartz Crystal Units, R. M. C. Green-idge, this issue of the B. S. T. J. 272 BELL SYSTEM TECHNICAL JOURNAL the other hand, the use of a relatively long etch, 30 minutes or more, isdesirable when a high Q is desired. The long etch also results
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