Re: Large Flat Coil

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "James Zimmerschied" <zimtesla@xxxxxxx>

Bart,
that is an impressive piece of work. It will be an event to see it in 
operation.
Jim Zimmerschied
----- Original Message -----
From: <mailto:tesla@xxxxxxxxxx>Tesla list
To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
Sent: Sunday, April 29, 2007 9:49 PM
Subject: Large Flat Coil

Original poster: "Barton B. Anderson" 
<<mailto:bartb@xxxxxxxxxxxxxxxx>bartb@xxxxxxxxxxxxxxxx>

Hi Everyone,

Today (Sunday) I took some frequency measurements of a large flat
coil I've been working on (slowly). There have been some mishaps with
wire purchases (beware of eBay). Anyway, I just thought I'd share for
anyone interested. If no interest, hit the delete key. BTW, this is a
1/2 scale replica of Tesla's famous flat coil. I just didn't have the
space for a full size replica.

Flat Coil Specs:
ID:  3.625 (hv end)
OD: 50.625 (rim grounded end)
Turns: 95
Wire: 18 awg magnet wire

Here's a couple photo's of the wound coil.
<http://www.classictesla.com/flat/Img_3462_fast.jpg>http://www.classictesla.com/flat/Img_3462_fast.jpg
http://www.classictesla.com/flat/Img_3461_fast.jpg

and other misc photo's:
<http://www.classictesla.com/flat/>http://www.classictesla.com/flat/

Measurement:
Coil set on a wicker stand providing a base height of 31.25" (coil is
parallel to ground plane). Below the stand, a 36" flat metal plate
was used as RF ground. I used a planewave antenna for the scope
measurements which was about 5 feet from the edge of the coil.
Because the flat coil is in a horizontal position, the planewave
antenna at the coils height would have negligible extC. Hooked low
impedance amplifier to the scope at it's base (which is the outer rim
end of the winding). Nothing of course is connected to the inner
winding end. Freq generator fed the z-amp. All this was measured out
in the backyard. Besides the house wall, there is a cement brick wall
along the entire yard about 10 feet high.

Fres measured 438.5 kHz. I tried to measure f2, but the generator
just won't output a high enough frequency (a thorn in my side a long
time now). Anyway, Javatc measured 455 kHz using measured radius
values from center of coil to the nearest wall. I ended up having to
set the wall radius value to 39" which resulted in a predicted
frequency of 438 kHz. I checked it by inserting the planewave 6"
below the center of the coil (providing an effective 10.2" grounded
disc equivalent just below the coil). This measured 406 kHz and
Javatc predicted 407 kHz.

I'll have to retest this again at another time as the backyard is
narrow and there is also a good sized above ground pool within 10
feet of the coil (giant object). Front yard would have been better
(hind sight). I'll be off the list for 7 days (AIT Convention in San
Antonio). Because today was nice out, I wanted to at least start
measuring before I decided to go further with the coil.

The coil will end up with 91 turns (as originally designed). A
primary ribbon is to replace the outer 2 turns. Javatc is doing ok on
flat coils it appears. This particular rim grounded configuration
cannot be ran with the online version however. I ran this on an
updated version I'm working on offline. The new version will allow
more of these kind of geometry's, but there is also an update with
primary to secondary spacing that is still being worked out (the
actual proximity where both distance and height are accounted
[primary inside or outside with any geometry]). The online version
can of course do flat coils, but the grounded end cannot be
interchanged. This seemingly simple output is actually complex, so
it's taking some time to code.

Take care,
Bart