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RE: Snow on telly - Results :-(

Hi Richard / all,
                    I'm sorry to hear about all your TVI problems.
I know what a daunting task it can be trying to resolve them.

I use to run 10KW erp on the 144 MHz Amateur band from home, and I had
horrendous TVI problems!

My equipment was checked by the authorities and given a clean bill of
health, but the strong RF field overloaded my neigbours TV's.
I was able to stay on the air, once some of the TV's in the area had filters
fitted.

Unfortunately, We get no help, but only condemnation from the authorities
with regard to Tesla Coil's.
They are classed as illegal spark transmitters in the UK, and any
interference generated would most likely be "in band" on the TV receiver's
frequency. (i.e, not fixable at the tv set)

The only thing that attenuated the RF radiation from my coil was the Faraday
cage (which you have seen)

It was very effective at attenuating the low frequencies, i.e my coils
fundamental resonance through to the harmonics in the 20MHz region,
but it becomes increasingly ineffective as you go up into the VHF and UHF
spectrum.

Before I built the cage, I did similar tests, and came to the same
conclusions.

Despite what some may tell you, Tesla Coils do radiate a lot of harmonically
rich, high energy pulses, especially at VHF and UHF where lots of the
components in a TC circuit reach there natural resonant frequencies, and
become very effective antennas.

I am sure, as you surmised, that the primary coil's VHF self resonance is a
prime culprit.
The spark gap is another.
Sadly RQ/TCBOR pipe gaps seem to be particularly good at resonating within
the 400 to 700 MHz region (TV freqs!)
and the connecting cables complete the task of radiating kilowatts of pulse
power into the ether.

I am sure a Faraday cage would considerably reduce your interference on the
AM band.
Mine cleared all buzz off the band, down to 10 ft from the garage.
We could even hear signals on my coil's fundamental res. 20 ft away!
The low frequencies are simply not a problem.

I suspect that the phone line breakthrough you are experiencing is also LF
in origin.

As for why my cage is relatively ineffective at VHF/UHF;-

The 5 ft square viewing screen of 1/2" chicken wire "leaks" a lot at
VHF/UHF.

Gaps in the aluminium panels become effective slot radiators at VHF/UHF.

Power cables passing into the cage re-radiate VHF/UHF energy outside the
cage in spite of bypass filters to the cage wall.
(BTW, metal boxes and screens around gaps etc will do nothing unless the
connecting cables are effectively bypassed at VHF/UHF to the grounded box or
screen with filter caps)

Also, the ali foil cage panels have little effect on the magnetic component
radiating from the coil. (yes, I wish my garage was Mu-metal too!)

Having said all this, I have got my TVI down to a manageable level, but I do
keep my runs short and infrequent.

Please don't give up Richard!  
These things aren't impossible to overcome in residential areas.
It just takes a lot more time, patience and perseverance.

I'm pleased that your University is showing interest in your Tesla coil!

As to why our American friends seem to get away without major TVI problems
I'm not sure.

More space between houses maybe., cable TV., lower TV channel frequencies?
Whatever it is, there sure 'aint any difference between UK RF and good old
American RF!

Any of you guys over there prepared to comment (please)?

 Best regards everyone,    Martin Dale,  TCBON   (also G6ABU!)





 


> ----------
> From: 	Tesla List[SMTP:tesla-at-pupman-dot-com]
> Sent: 	Thursday, January 14, 1999 4:27AM
> To: 	tesla-at-pupman-dot-com
> Subject: 	Snow on telly - Results :-(
> 
> Original Poster: "R.E.Burnett" <R.E.Burnett-at-newcastle.ac.uk> 
> 
> 
> Snow on telly - Results of testing :-(
	>snip

	                   	Richard (Richie) Burnett.

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