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Re: Variation of secondary Q



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

Terry wrote:
> I hooked up a 2.5kV spark gap and high voltage supply to pulsed
> the coil.

> The voltage data...
> http://hot-streamer-dot-com/temp/Qvar/3-19v.CSV

> The current data:
> http://hot-streamer-dot-com/temp/Qvar/3-19i.CSV

The base current waveform contains far more information about the
coil than does the voltage signal. 

See the FTs,

 http://www.abelian.demon.co.uk/tmp/3-19v.ft.gif
 http://www.abelian.demon.co.uk/tmp/3-19i.ft.gif

Notice how the higher mode content is visible in the base current
but not in the volts signal.  There's enough info here to extract
the F and Q of the first 3 or 4 modes, which is very nice.

> current data with a 50 ohm termination on the cable:
> http://hot-streamer-dot-com/temp/Qvar/3-19i1.CSV

and the FT is in 

 http://www.abelian.demon.co.uk/tmp/3-19i1.ft.gif

which is better still - a much flatter frequency response.

> If you like one of these signal type the best, let me know.

Yes, the 50 ohm terminated current signal.  Not much difference
with/without the floating ground - not sure which bit you are
floating there.

I see that the Fres has gone up a little - circa 4%, was that due
to the departure of the fairly close E-field pickup?  If so then
we're definately better off without it!!

The mode spectrum extracted from the current signal FT can be
compared with previous modeled results for this coil,

         Now         Previous
       Measured       Modeled     Change
f1/4:   86.2 kHz      95.4 kHz     -9.6%
f3/4:  312.1 kHz     334.8 kHz     -6.7% 
f5/4:  486.3 kHz     509.1 kHz     -4.5%

The pattern of changes indicates that the external capacitance has
increased quite a bit.  The modeled results are for your toroid at
45" above ground, I guess it's lower down now, say around 36-38"?

You could well be getting a few tens of kV at the toroid in this
mode of operation - will that be safe for long term unattended use?
Does it cause any interference that might become a problem? If you
are OK to run like this, the HT pulsing idea is growing on me, 
because it makes the base signal usable, and the base signal
contains a lot of info.
--
Paul Nicholson
--