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IMPROVED_CODAN

2014-11-09 03:34  
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IMPROVED_CODAN
Applied to first audio tube of receiver. Tube is biased off by zener diode in cathode circuit, and keep alive current is supplied to zener from B+. Actuating codan, consisting of crystal, voltage-doubling rectifier, smoothing capacitor C2, and load, produces positive output only when signal is received from i-f. Crystal is at 1.1 center frequency. Audio is thus unblocked only when voltage of desired signal, as set by R2, is sufficient to overcome cutoff bias in cathode circuit.-R. L. Ives, Crystal Codans Give Accurate Receiver Tuning, Electronics, 33;22, p 113.