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>1MHz Tesla coils and Cell-Phone Blockage

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LAN_403

Plasma Lover

Tue Apr 28 2009, 08:05PM

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

Harry wrote ...

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

I understand, Harry. I'm sure that you're much better than myself when it comes to building coils, and you know much more theory, but from what I can tell you're more of a ham; is that correct?

Does a VTTC operate in a method similar to a ham radio, in that the output circuit is meant to be a tube amplification circuit with an antenna that is made for maximum power transfer (but in RF transmission, I suppose you usually use an antenna with your proper wave-length and directly coupled to the output circuit)?

I am interested in the similarities in common ham radio and Tesla coils and their electromagnetic radiation.

Steve Conner

Tue Apr 28 2009, 10:01PM

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

Hi all

Intentionally interfering with radio communications is of course illegal, but I don't see anything wrong with discussing it. After all, if we know how it happens we may be in a better position to avoid it.

Ham radio transmitters are quite different to Tesla coils. The electronics of a VTTC might be similar (though the signal from a VTTC is far below the minimum quality needed for communications) but the real difference is the antenna.

A radio antenna is designed to efficiently turn power into radio waves and minimise losses due to corona, etc. The most important design choice is to have a current loop that's the same order of physical size as a wavelength, and an impedance (ratio of voltage to current in the antenna structure) roughly the same as the impedance of free space, 377 ohms.

A Tesla resonator is designed to efficiently turn power into corona and minimise losses due to radio waves. This is achieved by making it physically small compared to a wavelength, and giving it an impedance that's seriously mismatched to free space. (A typical Tesla resonator has Z0 = 25k to 100k ohms.)

It has roughly a quarter wavelength of wire in it, but it can't radiate because it's coiled up in a small space.

FWIW, I once left my cell phone next to an operating Tesla coil by mistake, and it seemed totally unaffected by the experience.

Solid-state Tesla coils can be made to generate a fair amount of VHF and UHF interference, but it's not generated by the electronics. If you allow sparks to jump from the topload to other metal objects, it basically creates a UHF spark transmitter, similar to the apparatus used by Hertz and Bose. The shorter the sparks, the higher the frequencies generated. Bose got all the way up to millimetre waves, which was pretty impressive for the 19th century.

RayeR

Wed May 06 2009, 09:12PM

Registered Member #333 Joined: Mon Mar 20 2006, 06:02PM
Location: Czech Republic
Posts: 45

Yes everything is illegal, of course running TC too but who cares :)

GSM network is quite hard to disturb by RF interference. It uses digital coding which contains many error correction codes. And your phone is switching between many GSM cells. It's much easier to disturb AM radio or analog TV signal. From my experiences SGTCs cause much more EMI than SSTC/VTTC. SGTC can disturb analog TV. I guess the most radiation come from sparkgap where is extreme dV/dt, di/dt. TC resonator itself is a filter which mostly resonates at f0 but it is not ideal filter so some higher harmonics are also present. SSTC/VTTC runs smoothly and there are much less harmonics.
So I think TC is not good idea for making RF jam on such high frequencies, better you make a special transmitter with proper antenna or try magnetron from MO, heh :P

teravolt

Thu May 07 2009, 04:19AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

A marx or pfn into a resonator at the specified frequency like a helical resonator might work. To do this you would have to generate a fundimental or uper harmonic at the cell phone frequency. just think about it you would be the first one with a "3G tesla". cheap cellphone blockers are more cost efective. the only purpace for such a device would to destroy cell phones and if you can do that there is a market for a geto blaser killer just at my work

haxor5354

Mon May 11 2009, 12:43AM

Registered Member #2063 Joined: Sat Apr 04 2009, 03:16PM
Location: Toronto
Posts: 352

is it legal to block public wifi networks?

Tom L

Mon May 11 2009, 06:19AM

Registered Member #1931 Joined: Thu Jan 15 2009, 03:11AM
Location: Hobart Tasmania
Posts: 6

I'm guessing it could be considered a denial of service attack (illegal in most countries). Though they operate in an unlicensed part of the spectrum, so intent would have to be established.

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