This circuit is taken from the Progressive Communications Receiver in most of the recent ARRL Handbooks. Values for the 40 meter band are shown.
If you want the ultimate in a bandpass filter for 40 or 20 meters, check out the bandpass filters in "An Integrated Contest-Grade CW Station", Solid State Design for the Radio Amateur, by Wes Hayward and Doug DeMaw, Page 225.
Another set of bandpass filters can be obtained from a "Solid State Communications Receiver", Ham Radio, October 1975, Page 34.
For information on evaluating and adjusting double-tuned circuits for maximum performance, check out the article "The Double-Tuned Circuit: An Experimenter's Tutorial", by Wes Hayward, December 1991, QST, Page 29.
To find information on bandpass filters on the internet check out Bandpass and I.F. Filter Information at the QRP HomeBuilder web site. He has very nice 20 meter and 30 meter bandpass filters using either capacitors or transformers for matching to a 50 ohm input and output. Very good advice is given on building the filters.
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