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Snow on telly - Results :-(


Snow on telly - Results of testing :-(

Last Monday, I took the day of work to investigate and resolve the
television interference that my neighbours were experiencing.  There
was nobody at home,  so it gave me an ideal chance to try the many
things that were suggested to me by LIST MEMBERS.  I also got a few
photographs and a bit of video of the coil running.

For those who like to "cut-to-the-chase",  I was unable to solve the
TVI problem.  However, if you are interested,  here is a summary of my
actions and (lack of) results:-

1. Tried removing the entire secondary winding and toroid assembly,
   then running the TC and checking for TV interference.

	RESULT:	The TV interference was much brighter on my TV and one
		several houses away.  This made me think that noise
		generated in the spark-gap and primary circuit is the
		cause of the problem.

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.

	RESULT: He said that he could hear the raspy crackling sound
		of the TC anywhere on the AM band at 150 yards away.
		He turned around and walked back because it had not
		begun to fade away !

		( Since I am an electrical engineer by profession I
		was greatly disturbed by this and decided to limit
		individual run times to around 1 second until the
		problem could be rectified.)

3. Carefully checked for optimum tuning by adjusting the primary tap
   clockwise and anti-clockwise by a half turn to confirm equal
   degradation in tuning and performance.

	RESULT:	Tuning was spot on !

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.

	RESULT: No noticeable difference to interference or spark length
		at my power of 2kW.

5. Tried an RC snubber across the RQ spark gap and then across the
   primary winding.  Snubber consisted of a rolled poly 600pF cap and
   a bunch of parallel Carbon Film resistors (R = 150R.)  This should
   reduce the Q of spurious UHF resonances in the primary arrangement
   by absorbing the high frequency energy.

	RESULT: No noticeable difference.  The Resistors did get warm
		though,  so some power was being absorbed when it was
		connected across the spark gap.


6. Tried an RC filter at the HV transformer bushings.  Two resistors of
   1K 50W at each bushing and a 600pF cap across the transformer HV.

	RESULT: No noticeable difference. The power resistors did get
		hot quickly as expected.

7. Tried shielding the spark gap and fans in an grounded Al foil
   covered box.

	RESULT: No noticeable change to interference.


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.

	RESULT: No decrease in TV or Radio interference.  Live and
		Neutral did have very small glitches when the TC was
		running,  despite 2 common-mode filters and one
		differential mode filter.


By now I was beginning to realise that I was fighting a loosing battle
and decided to take a few photographs and a bit of video before people
came home from work.  The coil would then be dismantled.

Several hours after packing up,  I had a visit from a local telephone
company engineer who said he was investigating a fault he had
discovered on several lines in our area.

It is clear to me that continuing to operate my "low-powered" TC in
a residential area is not an option.  And I was shocked at the extent
of interference that I saw,  and surprised by the limited effect that
any standard engineering practices had on stopping it.

I am not beaten by many challanges,  but I am definitely beat by this !

But its not all bad news,  the pictures and video turned out great,
and a local University is interested in buying some of the TC parts.

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.


PS. TERRY F, Sorry for such a long post.


				Richard (Richie) Burnett.

				- Wishing I had a Mu-metal garage
					( in Newcastle )