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Questions: RFI Problems & Outdoor Ground

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quicksilver

Fri Mar 26 2010, 06:15PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I recently took a small coil outside and used a "pole in the earth" ground that I had used often for a variety of things.
Some days later a neighbor (rather far away) had asked me if I was having trouble with Radio Frequency Interference, in that he was getting all sorts of problems with his TV.
{He did not use that term but the essence of his question was clear}

My question is - how much 'possible' RFI can a Tesla Coil produce?
The specifics were: a small standard gap coil using a small NST of 7Kv which was grounded to a copper washed rod 6' in the earth. Nothing special about this coil - however the area was elevated (a hill in relation to the neighbor).
I simply wanted to see it at night, etc. The times my neighbor spoke of receiving problems WERE similar to the times I had used the coil. The probability of this small coil producing this problem were fairly high.

Should I avoid this type of ground to eliminate RFI? In setting up a coil are their specific problems with one type of ground (earth) vs. another? Please note that the interference was supposedly observed at quite a distance from where the coil was operating. Could this be an odd co-incidence or can a coil produce some types of RFI up to 1/4 mile away???? Does one "type" of coil (SGTC) produce more RFI than another?

I did a bit of searching & reading but I found limited information addressing this issue. I realize this could be a complex question(s) & any help in shedding light on the issue would be appreciated -Thanks.

HV Enthusiast

Fri Mar 26 2010, 06:35PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

How long are you running your coil for?

If you only run the coil for a few minutes, than i wouldn't worry about shielding. But if you are going to run it for hours at a time, then you probably want to think about some sort of shielding / filtering.

radiotech

Sat Mar 27 2010, 02:20AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Does your neighbor use an aerial to get the TV signal and what are the the frequencies of the channels he is experiencng trouble with?

If aerial, how far away is transmitter? Is it digital or analog TV?

lpfthings

Sat Mar 27 2010, 04:27AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

A tesla coil will cause interference to TV's for sure .. they emit a hell of a lot of RFI, as is evident when you hold up a fluorescent bulb around your coil

Goodchild

Sat Mar 27 2010, 06:02AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

With the size of your coil there's no way that he is getting RFI from 1/4 mile. Trust me I'm also a Ham radio operator and people complain that Ham equipment interferes with TVs too, which they do from time to time, but generally people just like to find some one to blame for there crummy reception.

HV Enthusiast

Sat Mar 27 2010, 01:06PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

lpfthings wrote ...

A tesla coil will cause interference to TV's for sure .. they emit a hell of a lot of RFI, as is evident when you hold up a fluorescent bulb around your coil

Not really. Fluorescent lights are illuminated because of the near-field EM fields. Tesla coils in actuality are terribly inefficient radiators and don't emit much RF.

As you can tell, a fluorescent bulb is only going to light within arms reach of most Tesla coils.

quicksilver

Sat Mar 27 2010, 06:08PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

The specifics (to the best of my knowledge) are: an analog TV and a seriously complex antenna system (of what type I do not know) with a digital box (I live in AZ so TV's signals need a box now). Out here if you are going to receive free TV you need a good antenna system - or you must pay for cable.
They will range from quality HAM + whatever you need for the TV signals to junk Radio Shack monsters. But every one has to have some form of real system....it's just too far from Phoenix & the mountains get in the way from Tucson. I just didn't think that little coil could make any serious waves. But I really was put off by the reality that where I live the signals ARE WEAK!

The freqs he was having trouble with are unknown.

The coil ran for 30 minutes (but on & off). This is a SMALL SGTC. But unique in that it's performance is rather decent for it's size. Very standard construction: most parts bought from Amazing1.com - & primary: flat, secondary wound on PVC. Tuned via web page.....Nothing special.

I will say that this area gets great "skip" when someone sets up a decent di-pole and has the time to work with it. The BEST DX I have ever heard was out here as well as the clearest international stuff on standard shortwave w/ a good radio-antenna match.
When I was quite young all the kids who had an interest in radio got very old powerful tube radios & made fences into antennas - & could hear inconceivably distant stations.

radiotech

Sun Mar 28 2010, 05:48AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

The Tesla coil may not be directly radiating the RF that is causing trouble. But if the coil is throwing off sparks, those sparks may be exciting nearby metalic structures which are oscillating/directing or reflecting signals at resonances controlled by their shape/size. These can range from loose siding/gutters/pipes and if those have chemical junctions a whole new slew of non-linearity signals can happen.

Remember, analog TV is just crappy old AM radio that shows interference to the eyes-The sound is FM and AM noise doesnt make it through the limiters. Severe interference happening at modulations around which TC's may be operating multiples of 15734 Hz can mess with a system called AGC keying, which adjusts the TV's gain only during sync intervals (designed to avoid random noise effects on gain setting).

If you can interfere with TV, you also can interfere with AIR radio. Planes use AM to talk to each other and the tower because although FM is clearer, FM radios tend to capture the strongest signal and exclude anyone else.

Steve Conner

Sun Mar 28 2010, 11:04AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

This is true.

Spark-gap Tesla coils are especially bad, even if no discharge is coming from the topload, the spark gap itself produces huge amounts of hash at all frequencies.

If you have any loose parts on your topload that are sparking because they're not solidly connected to the rest of it, this can cause large amounts of UHF interference. The smaller the gap the spark jumps, the higher the frequencies generated. I remember Richie Burnett explaining how he could take out TV reception (in the 470-860MHz band over here) by letting one of his SSTCs spark 1/16" to a ball of tin foil.

If you live in a quiet area in the country that doesn't have much ambient RF, that just makes things worse, because the TV and radio stations are weaker and easier to jam. (Though it's nice if you're a radio ham, until your pesky neighbour fires up his Tesla coil...)

Goodchild

Sun Mar 28 2010, 01:29PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Steve McConner wrote ...

If you live in a quiet area in the country that doesn't have much ambient RF, that just makes things worse, because the TV and radio stations are weaker and easier to jam. (Though it's nice if you're a radio ham, until your pesky neighbour fires up his Tesla coil...)

That sounds like me except that the pesky neighbour and the Ham are both me.

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