Re: H/D Ratios

To: tesla-at-poodle.pupman-dot-com
Subject: Re: H/D Ratios
From: Tesla List <tesla-at-stic-dot-net>
Date: Tue, 27 May 1997 08:17:16 -0500
Approved: tesla-at-stic-dot-net
Subject:  Re: H/D Ratios
  Date:   Tue, 27 May 1997 06:32:58 +0000
  From:   "John H. Couture" <couturejh-at-worldnet.att-dot-net>
    To:   Tesla List <tesla-at-pupman-dot-com>


At 05:55 AM 5/23/97 +0000, you wrote:
>Subject:       Re: H/D Ratios
>       Date:   Thu, 22 May 1997 08:46:30 +1200
>       From:   "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>Organization:  Wellington Polytechnic, NZ
>         To:   tesla-at-pupman-dot-com
>
>
>Dear List,
>           Please indulge me once again :)
>
>> I have seen several references to a physical 1/4 wavelength of wire
>> being used to wind a secondary. What is the 1/4 wave length based on?
>> Is it free space or based on some velocity factor? Is there some magic
>> to be had by striving for this.
>> 
>> Based on no facts at all my next secondary will have a H/D ratio of PI.
>> It just seems right.
>
>Love it :)
>     The quarter wavelength thing: In the distributed resonator, no 
>matter what the length of wire, the profile is 1/4 wavelength at 
>resonance. Well, that is _strictly_ true for no top load (or nearly 
>so because like a standard antenna, there is an end capacitance 
>effect that requires the physical length of the straight wire to be 
>somewhat shorter than the free-space length). As soon as one adds a 
>topload, the antenna/coil will resonate at a lower frequency because 
>of the additional capacitance. That makes the structure shorter than
>90 degrees electrically at its resonant frequency. The lower the L/C 
>ratio, the more the electrical length trends towards zero degrees.
     I'd better stop there. I think I may have started writing a book.

----------------------------  Big snip
>
>Other comments welcome,
>Malcolm

------------------------------------------------------------------

  Malcolm -

  I agree with you that the 1/4 wavelengths and antenna concepts for
Tesla
coils does not stand up to what is found with real world coils. In the
TC
data I have collected the secondaries of almost all of the coils do not
conform to the 1/4 wavelength theory either for the actual or electrical
wavelength.

  This makes sense because the TC is a resonant air core transformer
with a
copacitance load and 1/4 wavelengths are not important. The TC is a dual
RCL
circuit where both primary and secondary circuits  must have the same
resonant frequencies  for optimum output. TCs operate the same as
standard
resonant transformers and helical antenna concepts are not involved.

  The fact that the maximum voltage is next to the top capacitance is
typical for a transformer when the voltage is measured across the
secondary
coil with one end grounded. This is why any size capacitive topload can
be
used as long as the dual RCL circuits are in tune.

  Tesla always said his TC invention was not for Hertzian waves but for
currents. Helical antennas, etc. that are Hertzian wave devices are not
involved. I now think that the VSWR is also not involved because there
is no
transmission line to couple the coil and capacitor load. Note that an
antenna is a resistive load at the end of an RF transmission line. This
is
not the TC type of circuit.

  The H/D ratio concept has only to do with maximum inductance and
little to
do with transformer operation. However, higher inductance does mean more
output with resonant tranformers.

  John Couture