----- Original Message -----
From: captbrian <[email protected]>
To: <[email protected]>
Sent: Wednesday, July 05, 2006 8:23 PM
Subject: LF: Re: Re: Re: Re: Antenna Tuning
> ongoing thought, If you use half the fixed coil and all of the varying
coil
> in series [ F/2 - V ] you should come near to zero inductance with coils
> in opposition - certainly quite a low value.
Dear Bryan, LF Group,
For the variometer to go to zero, the mutual inductance has to cancel out
the self inductance of the fixed and moveable coils when they are in the
"opposing" position - in other words the magnetic fluxes generated by the
two coils when they are carrying the same current have to cancel out
perfectly, or they have to have a (negative) unity coupling coefficient.
This can never be quite achieved in practice, k is always less than 1, but
to get close you have to minimise the gap between the two coils. In the
usual design of variometer, the moving inner coil has to be considerably
smaller in diameter so that it can rotate to any angle inside the outer
coil, and this restricts the tuning range due to the large gaps required.
There are other geometrical forms of variometer that don't have this
restriction, and have a larger range of variation, getting closer to L = 0.
Cheers, Jim Moritz
73 de M0BMU
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