I still like that laminate strip with a copper foil glued to it, a teflon sheet for the dielectric?where the foil
overlaps?to form a cap.? The overlap is held firmly in place by a couple bare FR4 boards bolted onto it.?
Perhaps add a gimmick cap of a couple teflon covered wires across the overlap cap for final adjustments.
So a very limited tuning range once you bolt down the overlap cap, but good enough for?
hitting a digital watering hole or perhaps keeping a schedule on a particular frequency.?
From an online calculator, skin effect at 14mhz is around 18um (well under a thousandth of an inch) for copper.
So a strip of moderately thin copper foil on laminate is sufficient, very lightweight, winds down to a small diameter.
There are ways to make a good variable cap, I like the trombone scheme of QST Nov 1994.
Could simplify that by going to 1.5" copper pipe with a gear drive motor inside, a 1.25" pipe
covered by a teflon sheet being pulled into it by a motor driven screw, the loop flexes a bit as
the 1.25" pipe moves.? But that would take a week, the laminate plus foil might be working in a day.?
Lots of mag loops using teflon, is that considered good enough for the capacitor dielectric?
Will using laminate for mechanical support have some undesired effect?
Jerry, KE7ER
