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Re: [TCML] Mains Suppression Filter

For very large large coils I would suggest B type over A type as there is a greater filtering effect at the usual frequencies. If your coil's resonant frequency is over about 160kHz then type A would provide better filtration. While the 3dB mark is useful in RF broadcast and reception applications where far-field is what is being dealt, 3dB reduction is not enough for near-field protection from such high power RF sources. 3dB is only half/double depending on how you look at it.

From my experience though almost all of the RF that gets in to mains from a
TC isn't through the supply transformer but rather the large and often seemingly random path current takes between the topload and the RF ground. RF energy will capacitively couple to just about anything in the vicinity, including wiring in the walls or nearby conductive objects. It is through these paths that it finds its way in to the mains system.

-----Original Message----- From: Michael Gray
Sent: Thursday, April 04, 2013 8:21 PM
To: Tesla Coil Mailing List
Subject: [TCML] Mains Suppression Filter

Hi all

Unfortunately, I've been forced to put the construction of my coil on hold
for a couple of months as I've had very little time to myself - but I'm
back to it now, and it's nearing completion. Really excited!

I'm not sure if it's common practice to implement a suppression filter to
protect ones mains circuitry, but I would very much like to do so. The more
isolated my TC project is from the rest of the house, the better. So I've
had a look around for some devices that would do the job for me, and I've
come across this one from Schaffner:


The one in particular I'm looking at is the 10A version, with surge
suppression. But I could use some help understanding the datasheet!

Having looked at the attenuation vs frequency graph for the 10A unit, I can
see that the filter achieves its 3dB cut-off somewhere between 10kHz and
20kHz, for the "A" configuration - and it gives:

A = 50Ohm/50Ohm sym

I'm not understanding that completely - should I be looking at the "A" line
or another?

Secondly, I like this device as it has surge protection built in too, and
it gives the following info for it:

Surge pulse protection: 2kV

Is this a suitable rating for overvoltage? My understanding is this - I
already have a Terry filter with the safety spark gaps in place to protect
my NST, so I can more or less assume that no HV is going to make it back
into my NST and hence the only way for voltage spikes to appear on the
input side of the NST (i.e. mains side) is if the coil sparks out and
strikes something on the input side (or possibly through magnetic induction
on input wiring?). If this is the case, then the 2kV rating would be more
than adequate. So I'd appreciate a sanity check on this, as I have more
than likely missed something (it's quite late here in the UK).

Anyway I'd appreciate your thoughts and feedback on everything I've

Many thanks!
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