RF Interference : HELP!!!

To: tesla-at-poodle.pupman-dot-com
Subject: RF Interference : HELP!!!
From: Richard Quick <richard.quick-at-slug-dot-org>
Date: Thu, 22 Aug 1996 00:28:00 GMT
Quoting Graham Armitage <armitage-at-tiac-dot-net>:

> I am having a big problem with RF interference when running my
> coil. It is a small (1.5kW) coil completely surrounded by a 
> faraday shield (bird-wire). I have just placed a 16A line 
> filter in the input and I still have strong interference on 
> TV's and AM Radio. For the RF ground I buried large sheets of 
> flashing and copper tubing although only to a depth of 4 feet 
> as the ground is full of rocks. I water it regularly and even 
> that doesn't seem to effect it.

> I remember Richard Quick saying he ran a TC in the room next to
> the TV with no interference. Any suggestions would be most 
> welcome!

Ouch! 

It sounds like you have undertaken the basic measures to prevent
excessive RFI, but you are still leaking. My guess is that
somewhere, somehow, you have significant RF current leaking into
your 60 cycle ground. This can/will energize the grounded
sections of etched circuit boards (TV, radio, computer, etc). The
60 cycle neutral wire and the 60 cycle ground wire are most
likely commoned in your building (they are in mine): direct,
unfiltered/unchoked connections between your RF ground and the
building-ground/neutral wire will cause this problem. Look here
first by checking continuity between the building neutral/RF
ground with a meter. If you show a direct connection between the
60 cycle neutral and your RF ground then you must isolate this
connection and either remove it or place a filter/choke between
the two circuits to reduce RFI.

Richard Hull just posted here in the last week or so that RFI/EMI
filters can be run with any orientation. My CORCOM filters (No.#
F2411F) clearly depict an RF choke in the ground path. I choose
to place my filters and ground my equipment in such a fashion
that ground path contaimination is not a problem. With these
filters it is possible to place the integral RF choke in the
ground path in such a way as to prevent a low RF impedance
between ground paths. By physically and electrically isolating my
grounds I maintain a very clean 60 cycle ground/neutral wire that
can be used without a problem during low power (>2kVA) operation.

Even without any RF filters or chokes I have run coils up to 1
kVA without a problem by ensuring an electrical separation
between the RF ground and the 60 cycle ground.

Richard Quick


... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12