Re: THOR resonance freq. measurement results

["Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Tesla list wrote:

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

> Secondary measurement
> --------------------------------------
> I disconnected the secondary bottom from ground and connected the function
> generator hot lead to it. Func. generator cold lead heartened. Measuring the
> electric field with a scope probe. Setup using long shielded cable to
saty far
> from the coil. Top toroid included in the measurement..
> 
> I measured 3 resonance frequencies:
> 
> 65.46 kHz
> 222.75 kHz
> 346.3 kHz
> 
> Can somebody explain the error (these are not exactly 1st, 3th and 5th
> harmonics, why?) ?

The top toroid shifts all the resonances to lower frequency, but in a
very particular way. The main resonance moves to low frequency as is
well
known, but the other resonances approach the frequencies of the -even-
multiples of the main resonance -without- top load. The lower resonances
move less, and the higher resonances move more, as they see the top
load capacitance more an more as a short-circuit to ground. The problem
can be treated (approximately, as a vertical coil is not exactly a TEM
transmission line) as a TEM lossless transmission line terminated in
a capacitor (the top load), that shows exactly this behavior.
 
> I also measured the frequencies were the measured field amplitude was halved:
> 
> 65.72 kHz halved
> 65.46 kHz full
> 65.21 kHz halved
> 
> But I don't recall how to calculate Q from it. Could anybody help, please?

Instead of searching for the half field points, look at when it drops
to 1/sqrt(2), or 0.707 of the peak value. Q is then simply the frequency
of the peak divided by the bandwidth. Using the half field points,
multiply the same ratio by sqrt(3), or 1.732. In this case the Q is:
Q=1.732*65.46/(65.72-65.21)=222.3

> First I tried to measure primary inductor and capacitor connected as a series
> resonator, but I could only and always spot the secondary res. freq. Then I
> connected them as a parallel resonator, fed them with the function generator
> through a 0.1 ohm resistor and measured the resistor voltage (i.e. the
current
> sourced). I wrote down the points were the current was MINIMUM.

You could use a larger resistor. The presision of the observed null 
would be greater.

Antonio Carlos M. de Queiroz