Dr Ronald Stiffler SEC technology

[gyulasun]

Hi iQuest,

Yes, both the electrical length (coming from coil wire length and the hook-up wires and say the 100 Ohm
resistor legs) and the coil self capacitance (that includes all the nearby "things" too) are the major factors
in changing the resultant coil frequency. You can consider the second coil itself to be 'serving' as a capacitive
top load for the first coil that is driven from the generator at its 'bottom', so the first coil may be loaded
(hence detuned from its intended frequency towards a lower frequency) at its both ends.
But the first coil also 'serves' as a 'bottom' load for the second coil and the top of the latter may be freely
floating and is affected by say your also floating probe placed near to it.

It is okay that you keep an eye on observing and maintaining a voltage maximum at the end of the coils,
in fact it is a requirement to attain the highest standing wave at the quarter wave frequency of the coils.
I agree with your observation on the Doc's using two different size L3 coil: a logical step to compensate for
detuning. If the first coil is the driven coil and its 'loaded' frequency corresponds to the one coming from the
formula, then it should be the second coil that has a little longer wire to reduce its frequency to that of the more
heavily loaded first coil. Or whichever coil is loaded heavier, the other one should have a bit longer wire, that is.

You wrote: "A standing wave is at play here, as would be expected on a transmission line with an open end. 
I'm trying to distinguish between standing wave and LC resonant frequencies and to better understand their
relationship in this circuit."
My take on this is: the quarter wave resonance goes together with the highest voltage amplitude at the top or
'free' end of a coil or transmission line involved and also this yields the highest standing wave reflection.

Any loading at or mainly near the top part of the coil changes voltage and current distribution (i.e. the coil gets
detuned) and this should be compensated for to maintain the coil's quarter wave frequency at the desired
'formula' frequency. This may need either adding or removing some wire length to bring back the detuned coil to
the desired frequency.  You could compensate the capacitive loading effect by changing the frequency and you will
surely have a quarter wave resonance again, of course, but now not at the desired 'formula' frequency but below it.

Would like to add the following notice to the end of my previous post where I wrote this: "this should normally result in
two notches in the response with a peak in between if two such detuned series tanks are swept between two 50 Ohm
(or any other value) terminations."   So here is my additional notice:
In case of the series two L3 coils where there are no real terminations at the coil ends, the notches will become the
two peaks you see now on your FFT display and the peak between them will become the notch.   

Thanks for showing your nice tests.

Gyula
PS Edited for more clarity.

[gyulasun]

double post

[iQuest]

Hi Gyula:
  It's good to have you, Itsu and others here to discuss technical topics to gain a better understanding.  I gave some thought to your comments and brushed up on transmission lines.  I think I now have a better understanding about
how the velocity factor which I previously brought up is affecting my test results.  I'm including information that I'm sure you are well aware of but others may benefit from it.  Typically the characteristic impedance of a transmission
line is fixed by the geometry of two conductors.  But with the L3 coil we are working with a one wire transmission line and the 'characteristic impedance is purely a function of the capacitance and inductance distributed along the
line's length'.  Any change to the surroundings of the L3 coil(s) at close proximity will change its characteristic impedance because the characteristic impedance of a transmission line is equal to the square root of the ratio of the
line's inductance per unit length divided by the line's capacitance per unit length.
   A change to the sensitive characteristic impedance of the L3 one wire transmission circuit with an open end will change the velocity of propagation at which the signal travels, this will change the wave length which will change the
standing quarter-wave resonant frequency.  'The velocity factor is a fractional value relating a transmission line's propagation speed to the speed of light in a vacuum.'  'In the same way that the wavelength of a signal is the speed
of light divided by the frequency for free space, the same is also true in any other medium.  As the speed of the wave has been reduced, so too the wavelength is reduced by the same factor.  Traveling at a slower speed the signal
cannot travel as far in the same time.  Thus if the velocity factor of a coax cable is 0.66 (vp=1/√LC), then the wavelength is 0.66 times the wavelength in free space.  The advantage of using a coax cable with a low velocity factor
is that the length of coax cable required for the resonant length is shorter than if it had a figure approaching 1.' 
   So the L3 coil's electrical length and the capacitance and inductance distributed along its length, which is affected by nearby things, are the major factors that will determine the standing quarter-wave resonant frequency of this
one wire open transmission line.  I don't think that LC resonance is a factor in the peak frequencies that Itsu and I have demonstrated for the open ended L3 coil(s).  What is your take on my comments above and my assertion that
LC resonance is not a factor in the peak frequencies we are seeing with the open ended L3 coil(s)?
   In light of this better understanding I do not think that posting my tests with direct FFT connections is warranted, my results were similar to what Itsu demonstrated in his video.  The peak frequencies were much lower because
the L3 coil(s) no longer had an open end.  These tests were done primarily to better understand where the peak frequencies were coming from and I think, as noted above and based on your previous post, that I have a better
understanding of that now.

I performed the following tests to determine how the standing quarter-wave resonance of a single L3 coil is affected by the proximity of the test probe, I used my L3D coil and FG was kept at 1Vpp with sine wave output:
Test 1: FG directly connected to (a) and the oscilloscope FFT probe is capacitive coupled by placing it against the last L3 winding at point (c) per the setup reference picture previously posted (probe was laying on top of coil former as pictured).
Test 2: FG directly connected to (a) and oscilloscope FFT probe tip lined up perpendicular with last winding at the top end leaving a 1mm gap between probe tip and the last winding (probe was laying on surface perpendicular to coil former).
Test 3: Same as Test 2 with 5mm gap.
Test 4: Same as Test 2 with 10mm gap.
Test 5: Same as Test 2 with 20mm gap.
Test 6: Same as Test 2 with 40mm gap.s
Test 7: FG capacitive coupled to (a) and oscilloscope FFT probe tip lined up perpendicular with last winding at the top end leaving a 10mm gap between probe tip and the last winding (probe was laying on surface perpendicular to coil former).
L3 coil peak resonant frequencies:
Test 1: 18.9 MHz (insulated probe laying on top of coil former up against last winding)     
Test 2: 19.8 MHz (1mm gap)                                                                                                 
Test 3: 20.1 MHz (5mm gap)                                                                                                 
Test 4: 20.3 MHz (10mm gap)
Test 5: 20.4 MHz (20mm gap)
Test 6: 20.4 MHz (40mm gap)
Test 7: 27.1 MHz (FG capacitive coupled, FFT 10mm gap)

Reference links:
https://chemandy.com/technical-articles/sitting-waves/standing-waves-article6.htm
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-14/characteristic-impedance/
https://www.electronics-notes.com/articles/antennas-propagation/rf-feeders-transmission-lines/coaxial-cable-velocity-factor.php

A couple of relevant quotes from Corum brothers:
"It's not the physical length of the wire but rather the velocity inhibited electrical length of the helical coil which must be quarter-wave resonant (i.e., have forward and reflected wave-interference producing a standing quarter-wave resonance)."
"Virtually all high performance Tesla coils are velocity inhibited, distributed-element, slow wave transmission line helical resonators."

[TinselKoala]

It does my heart good to see reference to the Corum brothers.

This video of a model of a transmission line may be of interest to some:
https://www.youtube.com/watch?v=f4T5KKQjz0s

[gyulasun]

Hi iQuest,

You wrote:  "So the L3 coil's electrical length and the capacitance and inductance distributed along its length,
which is affected by nearby things, are the major factors that will determine the standing quarter-wave resonant
frequency of this one wire open transmission line. "
I agree and I would add the followings: in case we exite the L3 at one of its ends from a generator, the first resonance
is a quarter wave one if the frequency is swept from a low enough value upwards. So L3 will have a voltage maximum
at its open end and maximum current at its fed point at that frequency: the equivalent circuit for this resonance is a
series LC circuit. If the frequency of the generator is tuned further on higher, then a half wave resonance comes:
minimum voltage develops at the center part of L3 (while current is maximum here) and minimum currents will be
at both ends (while voltage is maximum at both ends). The equivalent circuit now is a parallel LC circuit.
The Doc probed his L3 coil in one of his earlier videos to show how the voltage amplitude changed alongside the coil
from one end to the other while the frequency was set for the standing quarter wave resonant frequency for that coil. 
This was also shown by Lidmotor in one of his videos. 
So L3 needs retuning whenever a top load pulls its quarter wave resonance away from the formula frequency and the
checking should happen by monitoring voltage amplitude alongside the coil length with a loosely coupled voltage
sensitive probe. Voltage maximum should be attained again at the top loaded end while a voltage minimum should be
at its bottom or fed end.

On your question:  "I don't think that LC resonance is a factor in the peak frequencies that Itsu and I have demonstrated
for the open ended L3 coil(s).  What is your take on my comments above and my assertion that
LC resonance is not a factor in the peak frequencies we are seeing with the open ended L3 coil(s)?

Well,  I often wondered what are the L and C values when an L3 coil is tuned to the standing quarter wave resonant frequency?
or say to the half wave resonant frequency while we did not change anything but frequency? 
Here is a good paper on the self resonance of coils and I think it includes useful information in several respects:
http://g3rbj.co.uk/wp-content/uploads/2014/07/Self-Resonance-in-Coils.pdf  It includes: coils inductance increases as
their series resonant frequeincy is approached from the lower frequencies.

And here is the site the file is included,  a good part of the site is devoted to coils self resonance and self capacitance:
http://g3ynh.info/zdocs/magnetics/appendix/self-res.html   A very thorough treatment is included in this file from the
owner of the site:   http://g3ynh.info/zdocs/magnetics/appendix/self_res/self-res.pdf 

These are useful pieces of information and certainly need some time to digest. 
Maybe I have not answered your question directly?

Gyula