Re: THOR resonance freq. simulation vs.measurement results

["Marco Denicolai" <Marco.Denicolai-at-tellabs.fi> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

"Tesla list" <tesla-at-pupman-dot-com> on 19.07.2000 19:57:39

To:   tesla-at-pupman-dot-com
cc:    (bcc: Marco Denicolai/MARTIS)
Subject:  Re: THOR resonance freq. simulation vs.measurement results



Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
>
> Original poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi>

> >To compute Z0 and T for a coil, use:
> >
> >T=(pi/2)*sqrt(Cm*L)
> >Z0=(2/pi)*sqrt(L/Cm))

> I made a quick and dirty model with MicroSim at
> http://www.saunalahti.fi/dncmrc/th_frq.htm. The 2nd and 3th res. freq. still
> don't match exactly: 240 kHz and 447 kHz instead of 222 kHz and 346 kHz. It
> seems like the model frequency shifting effect is less severe that what I
> actually measured.
>
> Any suggestion?

Hello Antonio.

>Try:
>
>T=sqrt(2*Cm*L)
>Z0=sqrt(L/(2*Cm))
>
>This models better the behavior of the coil (transmission line) at low
>frequency.
>Comes from the comparison between the output admittances of a lumped
>model and a transmission line model, up to second-order terms in
>frequency.

I tried but it didn't help. Eventually I used the old formulas and the
following
values:

Cself: 34.8 pF (predicted 27 pF)
Ctop: 42 pF (predicted 57 pF)

and I got:

f0   65.7 kHz  (measured 65.5 kHz)
f1   221 kHz   (measured 222.7 kHz)
f2   399 kHz   (measured 346.3 kHz)

This is the closest I can get with this model. See
http://www.saunalahti.fi/dncmrc/th_frq.htm.

>Some time ago I made measurements of the resonances of a vertical
>coil, and found that all the resonances were shifted to low frequency,
>not following the expected 1:3:5:7:... ratios of an ideal transmission
>line. Can you verify this by measuring the resonances without the
>top terminal?

It's a big operation to remove the toroid and the secondary: they are heavy and
big. If I was clever I would have done it before mounting the secondary in
place. I'll do that sometimes, if I have to.

Regards