TSSP: List Archives

From: Paul
Date: Fri, 15 Dec 2000 18:37:42 +0000
Subject: Re: [TSSP] Coils at high elevation

Concerning Mark and Malcolm's measurements at high elevation, I
asked about how the coils were supported and fed.

Malcolm Watts wrote:

> each coil was placed on some insulating material (can't remember
> what) so that the windings started at the 26" off the floor. After
> measuring the largest h/d, I removed the appropriate number of turns
> from the bottom of the coil and lowered the insulating platform to
> keep the starting height constant. The h/d=1 coil then was wound near
> the top of the pipe and the bottom of the pipe must have been on the
> floor by that stage.

> I had the strap running vertically from the bottom of the winding
> down to the floor and then along it to a very short piece of coax
> coming from the generator. 

> There was a minimum clearance of 6' including the scope
> probe from objects other than the support (pipe). Any less and
> proximity effects were plain to see. 

Thanks Malcolm. There's not enough stray capacitance from the feed
strap to account for the Fres discrepancy. Perhaps the static charge
induced on the insulating support and coil former needs to be taken
into account - I'm currently ignoring dielectric constants of material
supports and formers in the capacitance determination, maybe the
dielectric properties of the gas-pipe former are increasing Cint
significantly.

The minimum clearance of 6' is even more sensitive than I thought!

I do appreciate that you made the measurements with the aim of
tabulating Q factors rather than precision Fres - we are perhaps
trying to use these results too far beyond their intended purpose.
I'll just have to be patient and await some purpose-made measurements.

Cheers,
--
Paul Nicholson,
Manchester, UK.
--


Maintainer Paul Nicholson, paul@abelian.demon.co.uk.