TSSP: List Archives

From: Paul
Date: Tue, 29 Aug 2000 21:56:26 +0100
Subject: Re: [TSSP] Q mesurements

Terrell W. Fritz wrote:
> I will look at this again...

OK. I like to set the scope gain so the envelope spans
7 vertical divs at resonance, level shifted to +/- 3.5 divs.
Then I detune until its +/- 2.5 divs.

I found a problem in the calculation of skin depth, was using
a handbook formula, checked and it gave the wrong depths.
Fixed now and the calculated input impedances and Q factors are
revised,

For Terry's big LTR coil:

   ZMeasured   ZModel     QMeas  QModel
f1  408 ohms   140 ohms    36     148     With toroid.
f1  784 ohms   117 ohms    39     221     Without toroid.

Which makes a lot more sense, despite the apparent
differences!
I've got a reasonable confidence now in both Terry's
measurements and the computer model. The above measurements
and predictions would all be commensurate with one another if
there was a major additional source of loss in the 
resonator, one thats big enough to dominate the total loss.

I'm thinking of the ground plane, wonder if the coil is 
producing massive circulating currents. If so, introducing
some radial slits ought to make a big difference. I know
the inductance pull is not much, but that might not
be a good indicator. I've been doing some rough arithmetic
and it looks like the circulating currents in the ground 
plane could add several hundred ohms effective series
resistance into the coil, thats enough to give Terry's
measurements.

I'm just trying to get an estimate of how much it would
pull the coil inductance to see if that matches too.

--
Paul Nicholson,
Manchester, UK.
--


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