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Re: RE- RF Chokes (fwd)
From: Adam[SMTP:absmith-at-tiac-dot-net]
Sent: Wednesday, November 26, 1997 10:34 AM
To: Tesla List
Subject: RE- RF Chokes (fwd)
>TL>In an effort to protect neon trannies from RF, chokes are placed on the
>TL>secondary line of the neon. What I would like to know is what
>
> 50% of your thinking is half right...
Huh? I say he's 100% right. Most of us do in fact connect one choke on
each HV terminal of a neon transformer. This way, the HF HV that
develops across the main gap is not also placed directly across the neon
transformer's secondary, as it would be otherwise. Most of the voltage
is dropped across the choke, which appears as a high resistance
(impedance to be precise) to the HF AC.
Now, since the impedance of the neon's secondary is still very high, and
still subject to a large voltage drop across it, we usually take one
other measure to protect it- bypass capacitors. These are small
capacitors (500pF on my system) placed between each HV output of the neon
transformer and your RF ground. These capacitors act as a high impedance
to the 60Hz current from the transformer (5.3M in my case) by a low
impedance to RF kickback (2K ohm for my 160kHz coil). In short, these
caps shunt the nasties through a low impedance path around your
transformer.
Lastly, a safety gap is employed, as two separate gaps from the neon's
outputs to ground, in parallel with the bypass caps. This attempts to
set an upper limit for voltages applied to the transformer, by breaking
down when the voltage is unsafe. None of these protective methods are
failsafe, but when used together and used *crrrectly* they can keep your
neon alive for a good long while.
> Or for those with more social responsibility
> (not to say fondness for their stereo, computer,
> cordless phone, etc.) -- a full-blown line filter.
Good point. Some kind of filtering is a must.
>TL>frequencies are we supposed to be stopping reaching the neon?RF as far
>TL>as I can recall ranges from about 300kHz to 3GHz
> Rf extends from the top of the very-high audio range (circa
> 50-kHz) to several thousand GHz. (which will probably be the
> clock speed of Intel CPUs in few years).
You mean the speed of Intel CPUs a few year after DEC, Motorola, IBM,
Exponential, etc... get there, right? I wouldn't hold your breath
waiting for a GHz chip from Intel; last time I looked they were still
clinging to their 1980's CISC architecture and maxing out their CPUs in
the high 200MHz range, expecting people to be in awe. The shiny colored
dancing clean-room-suited morons in their ads are clearly diversionary
tactics.
>TL>A Tesla coil's tank circuit I presume
>TL>would produce frequencies and harmonics covering a wide range of the
>TL>spectrum.
> The stray frequencies occur at even multiples of the
> fundamental and are important out to at least the tenth
> harmonic.
The tenth harmonic is certainly measurable, but the lower harmonics are
the ones to watch out for. Your chokes should provide as much
attenuation at your coil's operating frequency as possible. The nature
of the choke-bypass-cap set up is low pass and often a bit resonant, so
you must design for the cutoff freq of the filter to be well below your
TC operating freq.- preferably by at least a decade. If it is above the
operating freq, it will pass the bulk of the RF kickback and it is
useless. And if it is -around- the operating frequency it may ring
(resonate) and create voltages high enough to jump right over the choke.
Make sure the choke is large enough and insulated for high voltages!
-Adam
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Adam Smith
absmith-at-tiac-dot-net
Epoch, Inc. Digital Music Project
www.tiac-dot-net/users/absmith/ Now with MP3! Musik. Macht. Macintosh.
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