Re: RF filter question.

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

Original poster: "Steve White by way of Terry Fritz <twftesla-at-qwest-dot-net>" <slwhite-at-zeus.ia-dot-net>

I want to make a few comments about line filters. I think that most of the
line filters found on E-Bay, and I have a few, are of limited use for Tesla
coils. If you look at the 3 dB cutoff frequency of typical line filters
found on E-Bay, it is about 150 KHz. Some are less and some are more. If
your coil's resonant frequency is above 150 KHz, then these filters will do
an adequate job of keeping RF out of your power line. Most coils that I have
seen operate between 75 and 150 KHz. Large coils are even lower. Mine is
being designed to operate at 77 KHz resonant frequency. Typical line filters
have practically no attenuation at these frequencies. They are really made
to suppress "real" RF frequencies in the MHz range. There are line filters
available which do have substantial attenuation at typical Tesla coil
resonant frequencies. For example, CORCOM sells some newer design filters
( e.g. 15ET1) which are made especially for use with switching power
supplies. Switching power supplies generate substantial noise in the same
frequency ranges as typical Tesla coils operate. That is why they are ideal
and I recommend line filters designed for switching power supplies. The
moral of the story is that just hooking up any old line filter may not do
anything useful in the way of power line protection.

Steve

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, September 26, 2001 9:50 PM
Subject: Re: RF filter question.


> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi Vince,
>
> To protect the NST from the coil's RF, the following has become popular:
>
> http://hot-streamer-dot-com/TeslaCoils/Misc/NSTFilt.jpg
> http://hot-streamer-dot-com/TeslaCoils/MyCoils/BigCoil/protection.jpg
>
> For general AC line filtering, the many common AC filters can be used.
>
> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SmallCoil/small_ACwiring.jpg
>
> I like these Corcoms from DigiKey but they cost like $27 each!  You can
find
> similar filters surplus and such for 1/10 that...
>
> Radio Shack and many places sell MOVs (Metal Oxide Varistors) that clamp
> excessive voltages on AC lines.  These are very useful if the RF high
voltage
> "gets loose" :-))
>
> Cheers,
>
>         Terry
>
>
> At 09:23 PM 9/26/2001 -0700, you wrote:
> >
> > Hello People
> >
> > Being that I am gather the supplies still for my coil to get under way.
> > I now have several of the supplies to make the components.
> > I am curious about RF filtering for my NST's
> >
> > Should I make an RF filter or purchase one?
> > If I purchase one what should I buy?
> > If I make one, does anyone have a schematic I can follow for this?
> >
> >
> > Thanks
> >
> > Vince
> >
> >
>
>
>
>
>