Re: Variation of secondary Q

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Terry wrote:
> Ok, If the equation "Vin x Q = Vtop" is adequate, I can do a
> lot of things ;-) 

But you lose the advantages of the method proposed, in which
F and Q are computed from a captured ringdown waveform. 
The advantages are:

a) Insensitive to scope gain variation, and variation of field
pickup:  Doesn't matter how much the Y gain on the scope varies
from shot to shot,  and you should be able to move the field pickup
around without affecting the F and Q readings. 
b) Doesn't require you to measure anything on the coil, you can keep
well away, so that the experiment will be more stable.
c) Doesn't require you to manually tune a sig gen to Fres, so you
don't need to be in attendance at each reading.
d) Very accurate - the only calibration required is the scope
timebase, and this could be done by inserting a marker signal that
the software would pick up and align to.  Use a search coil eg
ferrite rod for the field pickup and tune it to some convenient
24hr long wave transmission so that a little of it appears in the
scope trace along with the TC signal.

If you don't want to tie up your scope, maybe one of those cheap
PC-based scopes would do.  You don't need stability, accuracy,
sensitivity, or high bandwidth, so a cheap bit of kit would do fine.
This also solves the problem of getting the data into the PC to be
filed in an un-attended way.

And you don't need to use the HP 33120a, just fire the coil base
from a 555.  Stability of the pulse amplitude is not required.

[current profile measurements]

> Is it ok if the secondary is slightly cone shaped for that test?

That's fine, the modeling software can do pretty much any profile
now.  Go for about h/d=1.0 with the winding - smaller h/d's can
be tested simply by leaving out the shorting links higher up. For
modeling purposes a thin-walled former, eg a light duty poly bucket,
would be best, because I still haven't got those dielectrics sorted.
If you wind an unbroken coil and then cut into it for the taps,
measure the first three resonances before and after cutting in the
taps.
--
Paul Nicholson
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