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Re: Sphere/Toroid Comparison Chart

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <tesla123-at-pacbell-dot-net>

John, Terry, All, 

I've tested my two toroids and my measurements "do not" agree with less than
20% reduction of Ctop. 
See below: 

Tesla list wrote: 
> Original poster: "John H. Couture by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net> 
> Terry - 
> I entered your coil's data into the JHCTES Ver 3.2 program to see what it 
> comes up with for a toroid. To get the 87.66 Khz the program came up with 29 
> pf for the capacitance. This is about 12% less than the graph shows (space 
> 33 pf) for an 8 x 30 toroid. On my web site I mention that the graph 
> capacitance would be reduced about 20% when placed on the TC secondary. It 
> appears this may be too high a percentage. We will have to wait until more 
> data is obtained.

I've been doing some toroid Fr tests the last couple weeks. 

Purpose: To measure the change in Fr vs. calc'd with two different toroid 
dimensions and also to check Ctop against Bert Pool's equations when C 
is placed on the secondary. 

Method: Frequency meter (0.1% accuracy at these frequency's) using Terry's 
TC Tuner. The secondary is set upon a pvc pipe stand (no primary). Toroids 
are lowered via pulley arrangement to measured distances. Tuner connects 
between bottom sec. winding and RF ground. Tuner dial is "finely" turned to 
acquire Fr indicated by led brightness. Tuner is measured with Frequency 

This may sound a bit odd, but the tuner measurement is within 1kHz of 
measurements taken via oscope and loop antenna (running) and I checked it
against E-Tesla6 (of who's Fr accuracy was less than 1kHz), so the method "is"
working. The tuner acts as a device that captures the Fr. Every coiler should
build one of these (it's so simple). Great job Terry! 

Toroids are precise measurements via circumference measurements: 
Toroid No. 1 = 7.7" x 32" at a calc of 35.2pF. 
Toroid No. 2 = 6.5" x  37.9" at a calc of 39.2pF. 
Secondary: 12.75" x 43.25". 

Toroid No. 1 (7.7" x 32") 
Level    CalcFr    MeasFr    CalcC     MeasC 
(inch)    (kHz)     (kHz)     (pF)      (pF) 

-1        76.8     88.8      35.2       21.0 
 0        76.8     88.4      35.2       21.4 
 2        76.8     87.8      35.2       22.5 
 3        76.8     87.6      35.2       22.1 
 4        76.8     87.0      35.2       22.7 
 6        76.8     86.8      35.2       22.9 
 8        76.8     85.9      35.2       23.9 
 10       76.8     84.7      35.2       25.2 

Toroid No. 2 (6.5" x 37.9") 
Level    CalcFr    MeasFr    CalcC     MeasC 
(inch)    (kHz)     (kHz)     (pF)      (pF) 

-1        74.2     82.8      39.2       27.3 
 0        74.2     82.6      39.2       27.6 
 2        74.2     82.2      39.2       28.0 
 3        74.2     81.8      39.2       28.6 
 4        74.2     81.3      39.2       29.2 
 6        74.2     81.1      39.2       29.4 
 8        74.2     80.6      39.2       30.0 
 10       74.2     79.7      39.2       31.2 

With Toroid No.1 data, the Fr ranges from 15.6% to 10.3% (closer to 
calculated Fr as toroid height is raised). Ctop for the toriod ranges from 
40.3% to 28.3%! That's a affect (possibly due to large coil?). 

With Toroid No.2 data, the Fr ranges from 11.6% to 7.4%. Ctop for the 
toroid ranged from 30.4% to 20.4%. 

Other than the obvious (reacts as one would expect) height changes, something
here does standout: 

Toroid No.1 is larger in cord diam. and smaller in outer diam. Thus, Toroid
No.2 is "physically" farther away from the secondary and therefore less
affected. Both toroids calc'd capacitances are similar, but toriod "proximity
in relation to the secondary" appears to play a major roll in both Fr and Ctop

I don't see a standard percent value we can throw to this (although anything is
better than nothing). I know my secondary is on the large side and might be why
my values for Ctop vary far more than 20%. 

If you have a huge cord size that is "suppose" to have a large Ctop value, 
you may be better off with a smaller cord size at a wider diameter (not 
because of the Ctop value, but due to the toroids proximity to the 

BTW, I also mounted the toriods on top of each other at 3" and 14" 
distances. By using 50% of each and applying these values to Bert Pools 
standard toroid equation (as d1 and d2), the accuracy was amazing (3% to 
0.6% from measured). I also swapped toroids (who was on top) and there was 
very little change (I didn't expect that). 

BTW, the above data's toroid height was measured from top secondary winding to
bottom plane of toroid. This of course was adjusted for center of toroid when
using E-Tesla 6. BTW, at a hieght of 0 on the 7.7 x 32 toroid (or 3.85" for
E-Tesla 6), I measured 88.4kHz and E-Tesla 6 predicted 88.49kHz. Pretty good
program and Tuner! 

For E-Tesla 6, wall distance is used, but often times there are objects around
that can affect Fr including my own body. One wall was at 80" and the other 3
were more than double that. I used the nearest wall at 80". Amazing program!
BTW, ceiling height is 120", and I did "not" include a primary in the program
(0 for all primary inputs - worked perfectly and was how I measured the coil).
The primary should change results and then possibly Ctop would be in the 20%
range or less. Maybe that is the next test. 

There is a proximity relationship here between toroid and secondary. I can't
conclude much until a smaller coil is tested with these same toroids and test
parameters (time to wind a 6" diameter coil). 

Just thoguht I'd share my results. Any thoughts from the list? 

Take care, 
Bart A.