Re: Non Linear Vac Cap?!


Immo, DL5KB
 

Barry,
your'e welcome. This experience is part of my worklife. 

By the way: beautiful work, your tuning-box.
Perhaps a little remark to this solution. The connection to the head of the capacitor elongates the loop on this side. So the mechanical middle of the loop is shifted half the length of this connection to this side. It may (I say it may!) change the reachable best SWR, because the coupling loop now is not at the point of zero of the loop. Using a gamma-match, you should search the new zero on the loop, with a coax coupling-loop it may have no such importance.
With an earlier built, I used a gamma-match and had to shift it abt. 3 inches for good result. The picture shows my first solution with a vac-cap on the bench, just with an ungeared Nema 19. My loop today has a 5:1 geared stepper and a coax coupling-loop.
73, Immo

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