Re: Snow on telly - Results :-(
> Original Poster: "R.E.Burnett" <R.E.Burnett-at-newcastle.ac.uk>
> 1. Tried removing the entire secondary winding and toroid assembly,
> then running the TC and checking for TV interference.
Makes sense.. The secondary, top load, and sparks are really the "load" on
the RF circuit and absorb most of the power, so without them, the power is
going into (as you have found) the radiation resistance (i.e. as an
> 2. Tried listening on an AM radio (not tuned in to anything,) and had
> a mate walk down the road with the radio to investigate the extent
> of the radiated interference. My friend walked about 150 yards
> away from the coil.
Almost certainly radiated then.. At 100 kHz, the fall off in field strength
with distance once you are EM propagating is going to be pretty low (and,
the AM radio has a whole lot of gain and a good AGC, so you'll hear it a
long way away).
> 4. Tried increasing grounding to 4 copper tubes, each 4 ft into watered
> soil. These were tied together with copper stip, and connected to
> TC parts by individual heavy-duty cables as described in my first
> post on this subject.
All that did was probably improve your system's effectiveness as an
antenna, although I think you are radiating with magnetic fields, where the
grounding isn't particularly important.
> 7. Tried shielding the spark gap and fans in an grounded Al foil
> covered box.
> RESULT: No noticeable change to interference.
You are radiating from the primary circuit as a loop antenna. Spark gaps
don't radiate much LF energy (VHF hash, yes, LF energy no)
> 8. Replaced my power transformers and balasting with a 600W neon, and
> retuned at lower power. Also I checked the LIVE and NEUTAL lines
> in the house with a scope.
And that confirms that it is your primary coil that is radiating...
> I would like to thank anyone who gave me guidance in this "black art"
> of interference suppresion. I will keep on the list and will be
> interested to read peoples responses.
Here is an idea... Assuming that it is the magnetic field from your primary
that is radiating (some of it couples into the secondary, but, most TC's
are loosely coupled), and the fact that the wavelength is really long, if
you were to put a second primary, wound the opposite direction, in series
with your existing primary and some distance from your secondary (so the
2nd primary DOESN'T couple to the secondary). Arrange the two primaries so
their axes are parallel (so the magnetic fields cancel, in the far field)).
This is a great way to make a terrible antenna.
There is some coupling from one primary to the other, which will screw up
the Lpri somewhat, but that is what tuning is all about.
The idea is to make so that the field(s) from your primary couple to the
secondary, but not to anywhere else.
> Richard (Richie) Burnett.
> - Wishing I had a Mu-metal garage
> ( in Newcastle )
And, of course, that was my next suggestion.. Actually sheet metal of any
kind would probably work, because the magnetic field would induce a current
in the metal which would cancel the field. Mu metal works well down to DC,
and, is really, really magnetically soft, so it shields against low level
fields. At your field levels, you could probably use steel siding.