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Re: Dynamic Q


From: Bert Hickman <bert.hickman-at-aquila-dot-com>

Tesla List wrote:
> 
> From: "bmack" <bmack-at-frontiernet-dot-net>
> 
> Hello again
> 
> I saw the the above term and liked it. I use boring terms like loaded
> Q.  Did Bert coin this phrase?
> 
> Anyway, what kind of numbers are you getting for dynamic Q?
> 
> I find that it's less than a tenth of the calculated unloaded Q
> (undynamic?)
> even before ionization and way before breakout.
> 
> Can anyone offer an explanation?
> 
> Jim McVey

Jim,

It depends. In the primary circuit, the gap is usually the biggest
energy loser. A primary LC circuit may have a measured Q of 75-100 (or
more) with the sparkgap "shorted". When the main series gap fires, I've
observed the effective Q of the primary dropping to the 10-11 range on
my system. Your mileage may vary depending upon the impedance of the
primary circuit and type of sparkgap. 

Similarly, a well-crafted secondary and toroid may show an instrumented
Q of 150-200... but under operation will typically show an order of
magnitude drop (or more) depending upon the degree that energy is being
siphoned off to generate streamers. And, if the primary gap fails to
quench, the secondary's apparent Q will appear to decline, since much of
the secondary's energy is now being transferred back into the primary
circuit. 

During a series of dynamic Q measurements I made a while back, my 10"
secondary's Q was about 150 (no streamers, based upon ringdown once the
gap quenched), dropping to about 19 under single-shot streamer breakout
conditions, then further dropping to about 10-15 under heavier
full-power air-streamer loading. A solid ground strike resulted in a Q
of less than 1, as the secondary's energy was very rapidly dissipated
(in under a microsecond!). 

If you are observing a dramatic drop in secondary Q and are NOT
achieving breakout, it's most likely an artifact of the main gap failing
to quench (very likely if you aren't getting breakout), and you're
actually seeing the secondary's energy being transferred back into the
lossier primary circuit. Measuring Q's on a firing coil is quite tricky,
since there are significant variations in bang size, streamer loading
and quenching all going on interactively, all at once! A storage scope
and some patience are essential! 

Hope this helps!

-- Bert --