Thanks to GW0OAJ for this article

Getting rid of approx 10 inches of capacitor lead made no noticeable difference to the filter response.  That meant that my chosen cascade coupling capacitance of 470 pF remained the business.  The response was then fine tuned to the centre of the QRP spot of 3560 KHz.  All in all, the insertion loss of 3.6 dB seems very reasonable.  After all, it is not a pre-amp and if conditions require the insertion, perhaps some more attenuation is called for on top of that as well :)

A very much expanded trace is shown, noting that the vertical scale is in 1 dB steps and that the reference level (straight pass-through) is the -10 dB line.

Saying that the response remained unchanged is not entirely true. What was very gratifying was that the wideband trace, covering up to 400 MHz, was flatline at -65 dB.  This was a most worthwhile improvement from the point of view of possible hostages to fortune in the shape of weird, unfathomable responses, sprogs and etc!  A bonus on top of the physical hardening of the pre-selector!

Conclusion:

A very nice little item from a "ready recipe," where there is perhaps more than meets the eye from casual reading, and the chef may have left a little something out.

Today I finished off the 80 metre pre-selector coil pack.  What an interesting little voyage of personal discovery; and not a little satisfaction in the actual construction!


I continued development and made a boxed version:

80m bandpass filter3

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