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With AM detection, a wider bandwith cyrstal filter is needed. A one 3.547 MHz crystal filter with two 39pf capacitors provides the bandwidth for AM listening. A little tighter bandwidth with a two crystal/39pf capacitor filter also works but seems to cut off the highs somewhat. The tighter bandwidth allows weaker stations to be received in some situations. |
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In this filter, all the crystals are 3.547 MHz to provide wide and narrow filters for listening to CW. The top filter uses 39pf caps for wide bandwidth and the bottom filter uses 100pf caps for narrow bandwidth. The Crystal Oscillator for the Second Mixer is 3.547 MHz to provide the 455kHz IF. |
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