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IF_FILTER_FOR_CW

2017-02-19 12:04  
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IF_FILTER_FOR_CW
Circuit acts Iike variable filter having adjustable bandwidth, with enough gain to compensate for insertion Ioss in CW receiver. Used to isolate weak CW signals despite noise and interference, as required in lowpower amateur work. FET input is directly coupled to collector of HEP55 serving as Q.multiplier regenerative amplifier. Transformer L1-L3 provides feedback. Filter is connected in serieswith input end of IF strip,following 1.2-kHz mechanical filter. When two CW signals are received, one can be eliminated by adjusting CA to recenter passband of filter. Current drain of 6 mA can be supplied by two 6-V batteries. For 455-kHz IF, C is 470 pF, CA is 7-45 pF, and L1-L2-L3 are 12-115-24 turns No.32 enamel on Amidon T44-15 core.-S. M. Olberg, Vari-Q Filter, Ham Radio, Sept. 1973, p 62-65.