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Re: Off-Axis Primary Inductance
Original poster: "Steve Cook by way of Terry Fritz <twftesla-at-qwest-dot-net>" <steve-at-g8cyerichmond.freeserve.co.uk>
One of the early ways of making a variable inductance for use in radio
tuning was to divide the inductance in 2 pancake type coils and then hinge
one relative to the other, by moving one relative to the other inductance
could be varied as far as I know it was never done commercially but I have
seen it used in amateur built equipment from the early 1900s.
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
Sent: Friday, July 05, 2002 6:28 AM
Subject: Off-Axis Primary Inductance
> Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Hi Coilers,
> For my next TC, I am thinking of having a fixed number of turns in a flat
> spiral primary, and some additional off-axis variable inductance in series
> with the primary. The variable inductance will be used to fine tune the
> primary resonance as the coil is operating. I am thinking the off-axis
> inductor will be two smaller spirals parallel to each other, with the
> spacing between them variable to change the mutual inductance.
> Can any of you help with the following question?
> Let's say the primary is of inductance L. Let's say I start decreasing
> primary inductance a few percent at a time, and compensate for it by
> off-axis inductance to maintain the same L. About what percentage of the
> total inductance can be off-axis before coil performance noticeably
> degrades? Anyone have some practical experience with this?
> I seem to remember a few years ago someone described an experiment of
> removing one secondary from a large twin coil, so the remaining coil had
> half it's primary inductance off-axis. I believe he said the performance
> was still very good.
> --Steve Young