Re: Off-Axis Primary Inductance

["Tesla list" <tesla-at-pupman-dot-com>]

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>
To: <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>"
<youngs-at-konnections-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
the
> primary inductance a few percent at a time, and compensate for it by
adding
> 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.
>
> Thanks,
> --Steve Young
>
>
>
>
>