This technique may be useful to gauge relative performance of the same coil with the same measurement technique to assist with tuning, but I'm not sure the results are comparable to anyone else's coil measured in a conventional manner. Just as the breakdown voltage of a multi-segment spark gap ten times 25 mils will be very different than a single 0.25" gap (a seldom-mentioned truth!), I suspect the same would be true with topload discharges.
I would also question whether the presence of nails conducting the discharge current might increase the capacitance-to-ground of the streamer and result in tuning to a lower frequency than if the nail segments were not present.
Regards, Gary Lau
MA, USA
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Dave Leddon
Sent: Tuesday, May 19, 2009 7:02 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Spark Length Measurement Techniques
Here's a scheme that I use to tune a coil to it's maximum spark
length which also yields an accurate measure the length achieved. I
tape a nylon weed-wacker line to the toroid and attach the opposite
end to a vertical support about 20 feet from the coil. Suspended
from the line are about 20 movable wooden dowels each pierced by
small nails at the lower end with the nail furthest from the coil
being grounded. An arc from a breakout point on the toroid will jump
from nail to nail to reach ground and so you just keep increasing the
dowel spacing an readjusting the coil until the arc cannot reliable
span the distance. Once the coil is tuned to achieve a maximum spark
length, all one has to do is measure the span and subtract the total
length of the nails.
Here's a picture this setup taken at Greg Leyh's Nevada Lightning
Laboratory last summer:
http://www.teslacoiling.com/firingthegap.jpg
Dave
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