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Re: reason for rf chokes?



Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Gregory Hunter by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ghunter31014-at-yahoo-dot-com>
> 
> > This spike returns to
> > the choke, which dampens the spike.  The choke is
> > essentially transparent at
> > 60hz, but highly resistive to the 200khz signal.
> >
> > larry.
> >
> >
> 
> Hi Larry,
> 
> Chokes alone are of questionable value in the NST
> filter role. A hi-Q airwound or ferrite core choke
> could, at least in theory, "ring up" to high
> potential, exactly like a baby Tesla coil, possibly
> doing more harm than good to your NST. Unless you have
> the ability to verify the lo-pass performance of your
> chokes throgh actual test & measurement, or at least
> the ability to computer model & analyze the chokes in
> your TC system, you are really just taking a shot in
> the dark.
> 
> As part of an LC lo-pass network, the chokes would
> have a better chance of providing useful filtering.
> Better yet would be an RC lo-pass filter with robust
> ceramic power resistors in place of the chokes, and HV
> caps to ground. Such a circuit is more predictable and
> practically immune to "ringing"
> 
> My .02$ worth,
> 
> =====
> Gregory R. Hunter

	I agree.  My simulations show a danger of such ringing unless both the
resistor and the "choke" are large enough, but the resistor is always
safe.  Remember that it has to handle the primary charging current, so
i^2R is worth calculating.

Ed