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Joined: Mon Dec 31, 2018 2:35 pm


Post by docstarz » Mon Dec 31, 2018 2:38 pm

Strange Coil, Unusual Propagation? (TORUS, TOROIDAL SHAPE)

Hi, newb here... am trying to hunt down some answers on how a specific coil will
propagate transmission under a few different conditions.

Photos of the coil and more details can be found at this link ; ... issues.htm

The basic questions I have are listed below - would greatly appreciate any menaingful

1.) Does the geometry of the coil affect signal propagation
For example, would this type of design tend to dampen propagation
Past the near field or would it work like a normal RF antenna?

2.) How far will the coil transmit frequencies in the range of 200 to
3000 Hz, at power levels between 500 to 1000 watts, given the
characteristics of the coil at elevations ranging between 1 to 6 feet?

3.) How do we calculate the ""permissible exposure levels" for this unit,
given inputs from # 1 above, for distance ranges of 1 to 20 feet
from coil?

tags ; antenna, torus,toroid,radio, frequency, engineer, engineering, signal, propagation,

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Post by TPT » Mon Dec 31, 2018 5:03 pm

Well, it might work as a power transformer, but not much good for anything above 60 hz. Put another way, shove enough RF into it, and it will radiate. Not very well or very far, but it will radiate. So will a dummy load, except the transmitter is less likely to either shut down or melt down.

Wavelength at 3,000 hz is just under 10 kilometers, a quarter wavelength 2.5 kilometers or 1 1/2 miles

Nathaniel Steele
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Post by Nathaniel Steele » Tue Jan 08, 2019 9:34 am

What are you intending to do with such a coil? By the way I followed some of the links, and most of them reek of psuedo-science, though I will admit to not having enough time to research the subject thoroughly, the presentation and lack of actual science presented reminds me of audiophile sites hawking magic power cables, crystal balancers for cd players, and "directional Cables". Once you get into the realm of free energy my BS detector starts to go off....I will admit the coil certainly looks like a work of art though!

Posts: 869
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Post by TPT » Tue Jan 08, 2019 3:23 pm

To elaborate further, 300 to 3000 hz is in the audio frequency range. Transmission facilities have been built in this range, but were not very efficient due to the length of a wavelength at these frequencies: (from Wikipedia article on extremely low frequency--ELF Rf transmission:

"The US maintained two sites, in the Chequamegon-Nicolet National Forest, Wisconsin and in the Escanaba River State Forest, Michigan (originally named Project Sanguine, then downsized and rechristened Project ELF prior to construction), until they were dismantled, beginning in late September 2004. Both sites used long power lines, so-called ground dipoles, as leads. These leads were in multiple strands ranging from 22.5 to 45 kilometres (14.0 to 28.0 mi) long. Because of the inefficiency of this method, considerable amounts of electrical power were required to operate the system. "

In other words, they ran cables on top of wooden poles just like a typical electrical power distribution system.

If you mean 300 to 3000 KHZ, that is the long wave band (still used by a few broadcasters and for aeronautical beacons) between 300 and about 400 khz, AM broadcast (530 to 1710 khz.) and some "shortwave" and amateur uses around 1800 and 3000 khz,

Typical long wave and AM broadcast use vertical antennas. For the most efficient radiation, an energized, insulated tower of at least a quarter wavelength is used. A "ground system,"--properly a counterpoise of a hundred or so buried radials, makes up the other half of the antenna. For example, for a radio station on 990 khz. a one wavelength tower would need to be about 300 meters high, while a 1/4 wavelength tower would be about 75 meters or around 250 feet. Ideally this tower would be surrounded by 120 radials (buried #10 copper wire usually) at least 250 feet long. For 500 watts, the safe distance from the base of the tower for RF exposure is about 6 feet. Since the towers are electrically "hot" they are fenced.

As you can see, the coil you show would be of no use for either purpose. A typical AM broadcast station uses small coils to match the output of the transmitter to the characteristic impedance of the tower. However, these are open-frame air coils. For little portable radios, you will find a small multi-turn coil wrapped around an powdered iron core used as a receiving antenna. No-good for transmitting, except maybe to "load" a short whip antenna with a fraction of a watt.

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