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secondary harmonic suppre
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TL>Date: Thu, 6 Jun 1996 22:25:16 -0600 From: Tesla List
Malcolm and all,
Here are a couple of points that I have been musing over.
The first relates to some work I did last year when I was
looking into helical resonators for use in a microwave
filter that I was designing.
In a standard helical resonator the device is a quarterwave
long and can be link or loop coupled (see the ITT databook
for a section). The problem is that such a resonator "throws
back" at harmonics by which I mean that a band pass filter,
for example, will have good out-of-band attenuation except
at harmonics of f (2f particularly so in elliptic designs).
The point is that there is a technique where the top third
of a coil is wound in the opposite direction to the first
two thirds. It struck me that it might be interesting to
wind a TC resonator such that the top third is reversed.
Apparently, if you do this, the harmonic response at 2f and
3f is dramatically suppressed and the first significant
harmonic occurs at 4f, by which time the amplitude is well
down cf. the fundamental.
My suggestion is that there will be less out-of-phase
currents flowing in the resonator; the secondary output will
be more coherent and the power in the fundamental will be
higher. If someone has access to a coil winding setup, it
would be interesting for that person to copy and existing,
proven resonator, but reverse the top third (i.e. if you
have 600 turns, make the top 200 go the other way). I would
imagine the sudden change in direction could be anchored
with a suitable adhesive blob.
The second point is one concerning instrumentation
techniques and I was wondering what has already been
attempted out of the following (TCBOR sound as though
they've tried most things and I would like to hear what
their experiences have shown):
1. Measuring the RF base current in the resonator being
pushed/pulled through the ground connection.
2. Measuring the current flowing between the secondary and
the extra coil.
3. Measuring the current flowing from the top of the
resonator in a two coil system or a 3 coil system, into the
capacitive load (toroid).
4. I read an article by Dr. G L Johnson in the 1992
Proceedings of the International Tesla Symposium which
discussed the construction of a capacitive V divider as part
of the toroid, and measuring the V across this small C as a
function of total output V. Has anyone seen/tried this?
I am presently getting the machining of my 1/2 HP 3000rpm
12" gap finished. When completed it will have 12 pegs that
can be removed (whilst maintaining symmetry and hence
balance) and will have 4 series gaps as a result of the
electrode arrangement. Each peg is 5/8" (16mm) stainless
steel (I couldn't afford tungsten). I will commutate my
10kVA 11kV pole transformer into my 1/2" Cu pipe primary,
using my 0.3uF pulse cap network (not homemade). I am using
a 20" diameter HDPE pipe as a secondary but this has a 1.5"
wall so I am considering cutting into collars to use as
support rings for a skeletal former. I think I read that
someone had tried three different formers and had seen
drastically improved performance from the one with the least
dielectric load ( i.e. a skeletal). I will then start
thinking about a biggish toroid (possibly 6 foot by 1 foot
or so).
The previous version of this device was built by myself and
my friend John Hewitt ( who has now emigrated to Boston, Ma)
and was run at the end of 1988 and achieved a discharge that
bridged a point to point gap that was a direct 55 inches (
arcs were upto 70" long I guessed, according to my notes of
6/1/89). This was from a 3kW input ( 16 lots of 10kV, 18mA
ignition transformers from oil-fired boilers phased and
paralleled) and an unterminated secondary. If I can find the
negatives, someone at work will scan them into a good
quality JPEG and then I can stick on a site somewhere, if i
can work out how!
Since the beginning of 1989, we have been redesigning and
acquiring bits ( new caps - new transformer - new secondary
wire ) and I don't expect to see any significant progress
much before Christmas (lack of space, time money, all very
familiar to everyone). However, just today it appears that I
might have some premises which I can use for a semi-
permanent lab. setup. Fingers crossed.
Richard Craven, England
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