FW: Miniature coils contest?

Hello Group,
Anyone built a small, <8" long secondary and < 0.5KW, coil
with high performance? By high performance I'm thinking
2x or more than the secondary length. Robert impressed me
with the following after my initial inquiry. For me it's a challenge
I can afford $$.
Did you hear about the coiler that stayed out to late. The first thing
his wife say as he walked through the door was, "Wire you insulate"
Sorry I think it's an old electrician joke.
Dave Huffman

From:  Robert W. Stephens[SMTP:rwstephens-at-ptbo.igs-dot-net]
Sent:  Wednesday, May 08, 1996 10:42 PM
To:  huffman
Subject:  Re: Miniature coils

>From:          huffman <huffman-at-d0tokensun.fnal.gov>
>To:            "'rwstephens-at-ptbo.igs-dot-net'" <rwstephens-at-ptbo.igs-dot-net>
>Cc:            "'David Huffman'" <huffman-at-d0tokensun.fnal.gov>
>Subject:       Miniature coils
>Date:          Wed, 8 May 1996 11:51:04 -0500

>Hi Robert,
>There doesn't seem to be much interrest in miniature coils in the
>I would like to summit my guess as to your small coils
>output. Would 8" streamers be close to what you got? This
>is truely a guess on my part. I was able to get 4" sparks from
>the "poor" system I threw together and it would seem that with
>a good capacitor and more sec. turns it would do much better,
>say by a factor of two. 
>I hope to some day see a 'real' coil in operation in the flesh.
>One that exceeds its secondary length. I am an electrical eng.
>and this stuff still seems like science fiction.
>Dave Huffman

Hi Dave,

Yup, not too much interest out there, but I thought there would be 
more academic interest Guys!

Your posting got my own interest peaked so I threw together a 
different little coil as follows.  Secondary was #29 enamel copper on 
the same size (1 & 7/8 inch OD black ABS) wound to a length of just 
6.5 inches.  Primary was 3 to 4 turns of #14 copper, solenoid with 
diameter of 4.5 inches.  Dual fixed gap spark gap with small blower.
Full 10KV -at-23 MA furnace transformer, two of my increasingly famous
Stephens Mega-Henry brand air core chokes, with safety gap across the 
transformer, and a large aluminum topload made from two plastic 
frizbees cupped together and covered with alluminum foil tape. For 
caps I used two good transmitting micas, .0039 mfd-at- 20KV each yielding 
0.0078 mfd. Operating frequency was about 850KHz.  The streamers
walking around the topload were a full 10 inches long!, but you need a 
darkened or totally dark room to best appreciate such a low power display.
Also the ozone and oxides of nitrogen from this little baby filled up 
the lab with a very obnoxious and unbearable odor very quickly, an 
effect which  (luckily) I don't get with my large multi kilowatt coils interestingly

This was the best I could coax out of it with the furnace 
transformer, perhaps with a 30 MA neon it would have hit my 
guesstimated 14 inches posted earlier.  Still, 10 inches represents 
1.5 times the secondary length.  Not bad.

The little guy I had mentioned before that was complicated by the 
insertion loss of a coupling loop produced 6 inch streamers, and was 
run from just 1/2 of the furnace transformer secondary.

Congratulations, your guesses where entirely within the infield of 
the ballpark!

I think there might be merit in establishing a contest, pick some similarly small
secondary coil
size as to length and diameter only, and also specify the transformer 
which could be used (like a 15KV 30MA neon, or a 10KV 23MA furnace
transformer, operated at exact primary nameplate voltage rating) and let
participants do whatever they wish to do within only
those constraints to make the longest repeatable and therefore 
verifiable streamer to a grounded target. 
Since the very idea of a contest should  be to inspire original thought 
and creativity  I think I would even open 
up the field to allow derivatives of the two coil classical design or 
even a typical 3 coil design now increasingly known as a magnifier.
However if multi coil designs are allowed, then the size restraint 
becomes somewhat meaningless unless you were to, for example, specify 
that the measured inductance of the final resonator must be equal to 
or greater than the sum total of all preceeding inductances within 
the rf circuit, but then there are clever ways of increasing system 
charging voltage by resonating the RF suppression chokes with the 
transformer secondary, so should these be included in the RF circuit?
Or should the ONLY criteria be the size of the transformer at rated 
voltage and all other parameters be available to be freely 
investigated?  I think that might be the best.

What kind of prize could be awarded besides peer group status?  Would 
that be enough?

What do you think of this contest idea?  Go ahead and post a copy of 
this communication to the net if you wish Dave and we'll see what if 
any interest there might be out there.  Or maybe a contest of sorts 
is already going on informally and the group doesn't have time or 
finances for another one?

As always, Happy coiling!, rwstephens