Q, Gaps, Etc
To: mail11:;-at-cimcad.enet.dec-dot-com (-at-teslatech)
Subject: Q, Gaps, Etc
From: I am the NRA <pierson-at-cimcad.enet.dec-dot-com>
Date: Tue, 18 Oct 94 21:08:47 EDT
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>I just bought a squirrel cage fan this past weekend to use with my
Wotsa multitube gap?
>I then tried the blower using an old single gap that I had made from two
>bolts. The secondary discharge with the blower on was about twice what I was
>getting with the blower off!
I bet it was.
Gaps are kind of an obscure art/technology. The old time wireless folk
put a lot of development into them. I have mucho old tyme wireless
books. I suspect that some of the Lindsay Pubs books on olde tyme
wirelss would be useful. The theory (for RF work) is that one wants
a _spark_ not an _arc_. They are different things. (There was an
_arc_ transmitter. Whole different thing from a spark gap transmitter.)
In general, a long gap is good. A cooled gap, or one which is "blown"
(as above) is better yet. A "quenched gap" consisting of smaller gaps
in series is as good, maybe better, depending on implementation.
best-best is the rotary gap. For small powers, it proably does not
justify the complexity, but for high powers, it is a win. Another
technique was to run the gap in something other than air, tho gains
here, versus a good quenched gap are minimal.
>And finally some questions: Does anybody know how to measure the 'Q' of a
Q == Inductance over reistance, as i recall.
But. Q of the coil is of less interest than Q of the _system_. Which
includes the resistance and losses in the capacitors, etc, etc. And if
the coil is running as a helical resonator (cf Corum & Corum) the Q gets
a bit more complex yet.
WITH THE MAIN POWER OFF....
Experimentally, one can excite the coil (or system) with a low power
signal, and measure the voltage. Excitation can be by direct
connection, coupling by a link turn or what haveyou.
Measure the voltage devoped across the whole coil.
Do this for a range of frequencies, from well below resonace to well
The peak is the resonant frequency. The "slope" indicates the "Q".
A high Q coil/system will have very little voltage when "off
resonance" even a little and a higher "magnification" on resonance.
Plot the voltage values against frequency.
To get high Q, use "Fat" wire. or flat strap. (tho strap is not
The voltage measurement will require a voltmeter that is OK In the
frequency of interest OR a 'scope or... (It has been argues that
most of what Tesla was doing in Colorado Springs was measuring the Q of
the system, and pushing it as high as possible.).
The low power excitation is typically a signal generator, one with
digital control makes getting the frequencies accurate easy, but is
A note of introudction:
I work with RF problems, and high voltages, some.
I am one who approaches Tesla and "his technology" as straight