Tom,
Several years ago I designed and built a few of these filters. The lowest
frequency one I built tuned 4-20 MHz. It is complex consisting of 9
inductors (toroids) and a 3 section 20-365 Miller type 2113 variable
capacitor. It does work fine but mine only had a Q of about 5 (0.8 MHz
bandwidth at 4 MHz). I think it could be scaled to 160 Meters (with a
300-400 KHz bandwidth) but it is not for use at high power (over 50 Watts).
I'd recommend that you design a single three pole band filter, perhaps like
the so called Cohn filter, and place a 3 section capacitor across the
sections to tune across the 160-meter band. Since I presume you only need a
single band, you could design a higher Q type than I did thus
simplifying the design. It's not a simple job but the performance can be
quite impressive.
73,
Joe, W1JR
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