Re: A photographic tutorial of Pancake Coil winding...with movies...(fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 22 Jun 2007 13:32:30 -0500
From: Bert Hickman <bert.hickman@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: A photographic tutorial of Pancake Coil winding...with
    movies...(fwd)

Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Fri, 22 Jun 2007 07:12:37 -0500
> From: David Thomson <dwt@xxxxxxxxxxxx>
> To: 'Tesla list' <tesla@xxxxxxxxxx>
> Subject: RE: A photographic tutorial of Pancake Coil winding...with
>     movies...(fwd)
> 
> Hi Bart,
> 
>>> Bart just pointed out that the metal pipe you are using acts like a 
>>> waveguide, or third coil.  
> 
>> Just the opposite. A third coil not in resonance acts more 
>> like a capacitively coupled topload object and the dimensions 
>> of the coil. The third coil is pretty much a pipe at that 
>> point. In Jeff's case, it's nothing more than a topload 
>> object. In your coil, the solenoid is acting like Jeff's pipe 
>> (just a topload object).
> 
> It may be an opposite perspective, but it is the same thing, either way.
> 
> A third coil has no inductive coupling with the secondary and acts like a
> Helmholtz resonator.  
> 
> If my understanding is correct, anybody can replace the third coil on their
> magnifier with a copper tube of the same dimensions and get the same
> results.
> 
> Dave
> 

Hmmm... this simply doesn't sound quite right.

In a properly tuned magnifier, the third coil is excited directly via 
base drive RF current (when the third coil is isolated from the driver) 
or via a combination of base drive and transformer coupling (when it is 
also magnetically coupled to the driver). The key is that excitation of 
the tertiary coil is done at the natural resonant frequency of the 
tertiary and topload (in situ). Under these conditions, the tertiary 
coil develops significant additional voltage above the voltage at its 
base. It is an active participant in further voltage multiplication and 
not, simply, a simple conductive cylinder.

Because it uses a comparatively small diameter and lightly loaded 
secondary, your magnifier is operating with a primary circuit that 
resonates at a much lower frequency than the first resonant peak of your 
third coil resonator (in situ). Bart's earlier analysis estimated that 
your tertiary coil was resonant at about 1300kHz while you measured your 
primary at 428 kHz. Because your driver is oscillating at a about 1/3 of 
the resonate frequency of the tertiary, you are getting very inefficient 
energy transfer between the secondary and tertiary coil. Consequently, 
there will be little additional voltage contributed by the tertiary 
coil. Under these conditions, your thin tertiary coil actually "looks" 
much like a conductive tube to the pancake coil below in terms of how it 
"loads" your pancake secondary. That's why Bart suggested that it might 
be modeled this way in JavaTC (from an electrostatic and capacitive 
loading standpoint).

However, this does NOT at all mean that your third coil is behaving like 
a waveguide (i.e., with resonating E and H fields INSIDE the tube). With 
the given geometries, you are over 1000X times too low in frequency to 
be seeing waveguide phenomena. For a variety of reasons, your secondary 
would make a very poor waveguide at GHz frequencies. Given the above, I 
don;t believe that Helmholtz resonators (audio frequency sound 
resonating chambers) apply to the physics of your system (or for 
magnifiers in general).

Bert
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