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Re: filtering question



---------- Forwarded message ----------
Date: Sun, 28 Sep 1997 17:06:50 -0700
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: filtering question (fwd)

Tesla List wrote:
> 
> ---------- Forwarded message ----------
> Date: Sun, 28 Sep 1997 14:25:30 -0600 (MDT)
> From: Chip Atkinson <chip-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: filtering question
> 
> From:   braino-at-mindspring-dot-com[SMTP:braino-at-mindspring-dot-com]
> Sent:   Thursday, September 25, 1997 5:02 AM
> To:     Tesla List
> Subject:        filtering question
> 
> I am finishing up my new power supply cabinet and I have a few questions
> about filtering.
> 
> First of all, I used to run small self wound filter chokes on my nst
> powered coils, mainlny to protect the nst. (these were on the hv side) But
> now I am running a 5kva pole unit. Are these hv/hf filter choke coils still
> needed?
> 
> Concerning RF filtering in the power cabinet itself, I have a Sprague
> Electric RF Interferance Filter Model No. JN10-1501F1.   It is a 3x40amp
> 240v RFI filter.
> It is labeled "Load" side, and "Line" side.  I am assuming that this was
> designed to remove RF eminating from the line side, before going to the
> load, hence it's orientation. Of course, in our situation, it is the load
> that is producing the RF, so should the orientation be reversed, or does it
> matter?
> And will this provide adequate line filtering?
> 
> Thanks
> .rob

Rob,

The pig will withstand virtually any abuse your coil can dish out... and
filters are not necessary. However, filters may be somewhat effective in
reducing the amount of high frequency radio frequency interference (RFI)
radiated when your spark gap fires. This "hash" comes from the shock
excitation of the parasitic inductance and capacitance associated with
the wiring between your pig and the spark gap. The longer the runs
between the pig and the gap, the longer the "antenna" that's radiating
this hash. To reduce it, filters would need to be installed physically
close to the spark gap, and in series with the HV feeds going back to
the pig. I'm not aware of anyone actually making any before-after
radiation measurements, however...

Re: the power-line filters, your suggestion that they be reversed makes
sense, since it's the coil that's the generator of the interference, not
the receiver. Practially speaking, it really doesn't matter very much as
long as you use the type which has coupled series chokes in EACH line
and caps on either side. Note, you MAY want to add a rather LARGE, high
voltage cap (say 10 uF or more at 1000 VAC) directly across the mains to
help absorb kickbacks. A large industrial MOV (1000+ Joules) rated for
240 Volt operation is also not a bad investment. The combination may
help save the more sensitive electronic equipment that's also tied to
your house mains. 

-- Bert H --