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20_METER__DIRECT_CONVERSION

2014-11-16 05:37  
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20_METER__DIRECT_CONVERSION
Well-designed circuit provides pleasing polarity and depth of sound, with SSB signals seeming to stand out against nearly noiseless background. Covers entire 20-meter band. Use of balanced-product detector improves stability to reject strong broadcast-band AM signals. BFO energy from Q4 is injected through center tap of broad-band toroidal transformer L4-L5. Except for preselector, selectivity is obtained only through shaping of audio channel. Bandwidth is more appropriate for CW if C7 is increased to 0.02 or 0.047μF. T1 is 10K to 2K CT Stancor TAPC-35.L2 is 40 turns No. 30 enamel on T-37.6 core, with 2 turns No. 28 on it for L1 and 4 turns for L3. L5 is 16turns No. 28 on FT-37-63 core, with center tap, with 4turns No.28 on it for L4, L6is 19turns No. 28 on 7-37-6 core, tapped 7 turns above ground.-J. Rusgrove, A 20-Meter High-Performance Direct-Conversion Receiver, OST, April 1978, p 11-13.