. The Bell System technical journal . Fig. 12—Filter testing area. The standard-lrequeiicy uuileib art- st-fiiabove the test sets. of each filter section is brought to a peak at a specified frequency. Thefilter is placed in a test shield simulating its final container. Voltagefrom a precision oscillator is applied to the input terminals of thesection and the voltage at the output terminals is measured with asensitive detector preceded by a variable attenuator. The condensersdesignated Ctl in Fig. 13 are adjusted with a non-metallic tool untilthe loss reaches a peak of 50 to 70 db. Each section
. The Bell System technical journal . Fig. 12—Filter testing area. The standard-lrequeiicy uuileib art- st-fiiabove the test sets. of each filter section is brought to a peak at a specified frequency. Thefilter is placed in a test shield simulating its final container. Voltagefrom a precision oscillator is applied to the input terminals of thesection and the voltage at the output terminals is measured with asensitive detector preceded by a variable attenuator. The condensersdesignated Ctl in Fig. 13 are adjusted with a non-metallic tool untilthe loss reaches a peak of 50 to 70 db. Each section contributes twosuch peaks. Ctl Ctl onM^ ckOQO/. Ctl Ctl Fig. 13—Schematic of crystal channel filter. TMV) nM^ 530 BELL SYSTEM TECHNICAL JOURNAL The filter is then transferred to a resonance bridge and the impedancelooking into either end of each section, with the opposite end open-circuited, is adjusted to series resonance at a specified frequency bymeans of the condenser Cr. This adjustment primarily controls theshape of the loss characteristic of the filter in the transmission resistance at resonance is recorded for later reference. In some types of filters, adjustment must be made to secure thecorrect absolute capacitance between certain points in the filter ratherthan to obtain desired attenuation peaks or resonances. A capacitancebridge is employed for this purpose. In all of these adjustments, test leads connecting the filter to the testset play an important part. Shielding, balance, capacitance to ground,dielectric loss, stability and other characteristics of the leads must becarefully controlled or compensated b
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