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>1MHz Tesla coils and Cell-Phone Blockage

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LAN_403

Plasma Lover

Sat Apr 25 2009, 11:55PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Has anybody on the forum ever made a Tesla coil and been able to block out radio communications (such as cell phones) with it? I was just wondering if it might be possible with the system that we're using for SGTCs and VTTCs and if it has ever been observed.

Dalus

Sun Apr 26 2009, 12:02AM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

It might be possible although it's illegal to block a cell-phone network. So I think this discussion is going to end in an early grave.

aonomus

Sun Apr 26 2009, 12:03AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Quite illegal to intentionally block public communications, but also note that cell phones operate into the 100's of MHz to a few GHz, where no tesla coil will go.

IBTL

Chris Russell

Sun Apr 26 2009, 12:19AM

... not Russel!
Registered Member #1 Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052

You might see some effect just by the strong signal desensing the receiver, but the effect will vary greatly depending on the phone, and will require very close proximity. Transmitting at 100W in any of the 1.8-30MHz ham bands does not interfere with my cell phone at any significant distance from the antenna. If you're radiating even a fraction of that amount, you're just asking for a visit from the FCC.

Plasma Lover

Sun Apr 26 2009, 04:22AM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

I understand the potential legal ramifications of attempting such a feat, but I was simply wondering if it were possible to do with a Tesla coil, because my small Tesla coil (3/15 NST) doesn't interfere with any communications (other than maybe radio).

Thanks for the input, guys!

Proud Mary

Sun Apr 26 2009, 05:22AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Many of the Tesla designs I've seen here and elsewhere look as though they'd be rich in harmonics - the use of Class C and beyond - so it would be surprising if they didn't cause interference at intervals well into the hundreds of MHz.

One need only think of the 100kHz crystal calibrators that used to fitted in communications receivers to see that anything approaching a square wave pulse will have this effect.

If there is concern about harmonic interference, and other spurious emissions, perhaps a few popular designs should be examined with a spectrum analyser.

Where access to a spectrum analyser is a problem, a sensitive harmonics detector can be lashed together with a coil, (or better, plug in coils) a variable capacitor, a couple of diodes, an op amp. and a meter, a useful piece of kit to have anyhow.

Now, as for deliberately interfering with public telecommunications, this is clearly both illegal and anti-social, in that it could have bad and sad repercussions in the lives of others, as well as bringing amateur science into disrepute.

GeordieBoy

Tue Apr 28 2009, 12:37PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Most powerful SSTCs cause intense local interference to radio broadcasts in the hundreds of khz range that they operate in. Switching harmonics also cause interference across most of the MW broadcast band too. The key thing here though is that the interference is VERY localised. It is bascially desensitising the receiver when it is in the near-field of the TC.

Fortunately a SSTC designed to produce impressive sparks is a very poor radiator of RF energy. Most of the interference at these frequencies is actually conducted through supply and ground wiring rather than radiated.

It is possible to build a SSTC that radiates very efficiently, but then it is called a solid-state Long-wave broadcast transmitter. Given the nature of your enquiry i'm not going to elaborate on this any further though!

As for jamming cell phones, they run at ultra high frequencies that are well away from anything our solid state tesla coils produce. They also use things like spread-spectrum / frequency hopping techniques, so they are intrinsically very robust to jamming attemps.

My experience in a variety of different types of Tesla Coil has shown that conventional spark-gap Tesla Coils are far more polluting in the UHF spectrum and above, than SSTCs. My old spark gap TC used to generate quite severe TVI at 3kW and was, as Harry put it, "anti-social"! ...whereas solid state stuff is just so much cleaner and more well behaved in a residential environment.

-Richie,

Littlew

Tue Apr 28 2009, 05:22PM

Registered Member #1448 Joined: Sat Apr 19 2008, 01:16PM
Location: Russia/Moscow
Posts: 21

You can make 100mHz plasmatweeter with special tube, but all energy will be in steamer, to transmit it u need good antenna.

Plasma Lover

Tue Apr 28 2009, 05:57PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Littlew wrote ...

You can make 100mHz plasmatweeter with special tube, but all energy will be in steamer, to transmit it u need good antenna.

This forum was intended to be about Tesla coils and their unavoidable RF interference, and not methods of causing interference intentionally. If this thred turns to intentional methods of causing a broadcast of RF noise, I'm sure the Mods will quickly delete it, or the FCC will be knocking on Chris Russell's door. Or both.

Please stay on-topic if this conversation is to progress further.

On another note, I have seen a scope waveform of somebody's TC operating at a few hundred KHz, and in the waveform there was ringing that was in the MHz spectum. Is this ringing the 'First-Notch' ringing that is expected, or is it simply an unwanted harmonic, and how high into the frequency-range can these low-power harmonic go, for example, on a 1MHz TC (perhaps VTTC)?

Proud Mary

Tue Apr 28 2009, 07:00PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

A theoretical pure aquare wave may be considered as the superimposition of an infinite series of sine waves, so the more closely a TC follows an on-off switching waveform the worse harmonic interference will be.

As for VTTCs, very simple valve oscillators with few tuned circuits such as are common in Tesla designs, are perfectly capable of oscillating on more than one frequency at a time, especially if poor circuit layout allows feedback other than through the tuned circuit. There may also be parasitic oscillation, often in the VHF range, where the lengths of the valve electrodes, added to their internal and external wiring form a tuned line type resonant circuit. In extreme cases, parasitic oscillation can completely swamp oscillation in the desired range, but more often runs along side it, wasting power and creating interference over a wide area. Only very short conductors - lengths of circuit wiring - are needed to radiate efficiently at these frequencies.

I should stress that I am not a Tesla man, but these are my impressions from my knowledge of RF oscillators generally.

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