RE: Calculating secondary resonance of bipolar coils

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "sundog by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sundog-at-timeship-dot-net>

Hi Gavin,

 Yep, Terry got that one right on!

Just calculate for 1/2 the total secondary (otherwise your Fo would be for
driving the whole thing in a classic configuration).  Make sure you have the
two toploads (sideloads?) as identical as possible to keep "funny" things
from happening.  Just calc. out 1/2 the coil and 1 topload. The more turns
you have (2x a normal coil) the less a little error in # of windings,
topload size, etc is going to affect you when tuning.

 Where you'll run into fun isn't the tuning' as is the case with most coils.
It's the coupling.  You can use a flat primary on these and it works
beautiful (looks a bit odd).  My tiny testbed used 2.5" PVC with ~2k turns
on it, but the primary was too closely coupled and it died in a matter of
minutes.   Tuning is about like a normal coil (a bit more involved with
basically 2 coils).  I used a flat primary, though a helical will work also.
On the helical primary, I'd mark the middlepoint of the windings and move
both leads at the same time either towards or away from it.  Keeps your
middlepoints about the same.

 Good luck with it, these things are wild, fickle devices, but *man* does
that point-to-point arc look good!
													Shad

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, January 04, 2001 8:03 PM
To: tesla-at-pupman-dot-com
Subject: Calculating secondary resonance of bipolar coils


Original poster: "Gavin Dingley by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<gavin.dingley-at-ukf-dot-net>

Hi all,
I sent a mail to the list a couple of days ago regarding secondary bipolar
coil
resonance calculations. As there has not yet been a reply, I thought I
should
elaborate on the question I originally asked.
Most TCs are of the up-right quarter wave resonant type, topped with a top
load
such as a torroid. I have recently wound a secondary more suited for use as
a
bipolar or half wave resonant secondary. The primary is positioned in the
middle of this secondary coil; and the there will be no earth connection at
the
mid point of the secondary.
Now, I know that it possible to calculate the resonant frequency of a
quarter
wave coil using medhurst and the standard LC resonance formula. It is also
possible to treat the secondary as a Tx line by determining the wave
velocity
from the coil inductance and capacitance per unit length. Medhurst, I
believe,
was derived from empirical measurement, while the Tx-line method relies on
modelling. Either way, it seems that these methods do not work when
considering
half-wave resonators, the frequencies tend to be much greater than, say, the
medhurst calculation. So, has there been found a method of calculating the
half-wave resonance of a coil?

Thank you in advance for your help.

Gavin