Underground electrical signalling ?

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Externet
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Underground electrical signalling ?

Post by Externet » Tue Jun 19, 2007 2:34 pm

Hi all.

Being one terminal of electrical generation grounded to the soil at the power plants and at many other points in the distribution net, it poses an inconvenient to inject an electrical signal at one location with the intention of picking it at a distance.

Was thinking on how to apply isolation transformers for the task, but nothing comes to mind. :sad:

Any speculations or ideas on how to use the earth as a propagating media for some kind of long distance electrical communications? :shock:

Miguel
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Bob Scott
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Re: Underground electrical signalling ?

Post by Bob Scott » Tue Jun 19, 2007 3:16 pm

Externet wrote:Hi all.

Any speculations or ideas on how to use the earth as a propagating media for some kind of long distance electrical communications? :shock:

Miguel
Back in the very early "Marconi" days of wireless communications they tried transmitting by using the earth as an antenna. Just stick a couple of metal spikes in the ground a specifiic distance apart so that the earth is part of a folded dipole antenna.

I understand that very low frequencies below 100KHz allow submarine bases to send messages to submarines at very long distances. However with carrier frequency that low, modulation is slow and limited to morse code or ASCII character transmissions.

Bob :cool:

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Post by Chris Smith » Tue Jun 19, 2007 4:00 pm

Many RF frequencies travel along the ground as a pair of nodules, meaning they use the Ground and the RF as a co existent pair of mediums to transmit and carry properly.

However, Ground wires in a three wire system is terminated as many times as possible for safety reasons but the power and neutral wires are not.

RF down these wires is a success story and failure [interference] for the web, and many other means of communications.

Many Power companies send a simple signal down the wires piggy back with the voltage transmissions waiting for a failure.

When a line goes dead that signal is picked up in an instant, located, and then dealt with.

USB Cable signals do work on these lines but they have been reported as interfering with emergency and air frequencies, .......but this can be dealt with.

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Post by haklesup » Tue Jun 19, 2007 4:14 pm

Power is not transmitted through the ground, the neutral conductor serves this purpose. Ground is used as a universal voltage reference, the neutral conductor is connected to it at many nodes to ensure a constant voltage along its entire length.

Locally, ground also serves the purpose of being an infinite current sink, someplace to put all the current you want and still make it 0V. Obviously, local soil condition dictate on how well it works for this purpose.

As to VLF, I doubt its easy to get an FCC licence to experiment, especially since it makes ones head explode. (see below for proof )

From http://www.themareks.com/xf/1998.shtml

Entering California, a highway patrol officer on motorcycle hands Mulder a cell phone. Scully tells Mulder that she has learned that the Navy has part of an underground transmitting array for an ultra low frequency radio system (used to communicate with submarines) running under the Crump property. They had a power surge that morning that disrupted television in four states. Scully theorizes that the surge created a condition in the inner ear that is somehow eased by speed along magnetic lines of force, or some such reason. She will fly ahead of Mulder and meet the car where the highway ends, inserting a needle into Crump's ear to relieve the pressure. Crump agrees, as his only way to survive. But when the car actually arrives, Crump's ear has already exploded and he is dead.

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Post by Chris Smith » Tue Jun 19, 2007 5:14 pm

Frying pan frequencies are not limited to just to the ultra low frequencies, [miles per wave] the 450 MH range cooks the skull and bones just nice.

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Post by k7elp60 » Tue Jun 19, 2007 6:39 pm

I once built a device that measured the impedance between two metal poles driven into the earth. This was part of a project to inject audio frequencies into the earth via the two metal stakes. A digital audio generator fed a audio amplifier of about 20 watts. The output of the amplifier was about 8 ohms and this fed a tube type output transformer connected between the amplifier and the two metal poles. The impedance between the poles could be as I remember between 2.5K and about 15K. This device was part of system to detect buried metals. My mentor had actually built a similar device and was able to send music a number of miles.
If some one is really interested, I will see if I can find my notes etc.
Ned

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Externet
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Post by Externet » Tue Jun 19, 2007 7:58 pm

Well, Ned, anything helps, not for measuring the impedance, but sending music a "number" of miles has to be interesting, -with no airwaves-
I just do not see how an 'electrical' signal can be conveyed half globe away, regardless of speed, if the emitter and receiver ends are obviously grounded. But perceive there should be a way... hmmmm.
At least the oceans are more electrically conductive than soils; but grounded too. :sad:
Transmitting something referenced to ground, via ground... :?

Miguel :???:
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Post by rshayes » Tue Jun 19, 2007 10:34 pm

Communication using ground currents does work for limited distances.

This was demonstrated in the 1800's, by transmitting signals acrosss a river without running wires across the river. Not much came of these demonstrations.

During World War I, most of the military battlefield communication was done with buried telephone lines. This worked for communications between units in fixed positions, but burying the wires deep enough to withstand artillary shells took considerable time and manpower. Ground current systems were used for communication with units that had advanced past the limits of the buried wire network.

The basic idea is to drive two electrodes into the ground about 100 ft apart. An audio signal (in WWI high power buzzers were used) is connected to the two electrodes. This causes an audio current to flow between the electrodes. Some of this current passes through the ground at a fair distance frome the electrodes, and can be received with a second similar pair pair of electrodes. The electrodes should be parallel to each other for best coupling. The detector may be as simple as a pair of earphones, or an electronic amplifier can be added for better range.

The range that can be obtained depends on the power of the transmitt and the sensitivity of the receiver. Distances of about a mile might be reasonable. Greater distances may be possible if the electrode spacing can be increased.

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Post by Bob Scott » Wed Jun 20, 2007 5:56 am

Externet wrote:I just do not see how an 'electrical' signal can be conveyed half globe away, regardless of speed, if the emitter and receiver ends are obviously grounded. But perceive there should be a way... hmmmm.
Transmitting something referenced to ground, via ground... :?

Miguel :???:
Well, think about the way those folded dipole FM antennnas that used to be shipped with every stereo worked. Just made from 300 ohm twinlead, yet one end is "shorted" to the other.

Ground is not magic. You can still set up a resonance between two grounded points that are a fraction of a wavelength apart.

Bob :cool:

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Post by Chris Smith » Wed Jun 20, 2007 8:17 am

ELF has been used as ground communications long before WWII, going back to Tesla's time. [miles per wave]

The navy has experimented since then and has many communications stations like the one up near Navato/ Petaluma which talks to subs half way around the world including under water communications.


Extremely low frequency (ELF) is the band of radio frequencies from 3 to 30 Hz. ELF was used by the US Navy and Soviet/Russian Navy to communicate with submerged submarines.

http://en.wikipedia.org/wiki/Extremely_low_frequency


Ultra Low Frequency (ULF) is the frequency range between 300 hertz and 3000 hertz. This band is used for communications in mines, as it can penetrate the earth. [1]

http://en.wikipedia.org/wiki/Ultra_low_frequency

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Post by haklesup » Wed Jun 20, 2007 11:41 am

I just do not see how an 'electrical' signal can be conveyed half globe away,
It's not an electrical signal being conducted (voltage or current point to point), its an electro-magnetic wave with sufficiently long wavelength so as not to be impeded by the earth when it is used as a transmission medium.

One needs a very large antenna for such applications.

Locally, or for short distances, electrical signals may be transmitted but it definately depends on the composition and impedance of the local geology as to how well it could work. Its like using a wire to transmit a signal but the wire is actually a bulk solid. The signal is going to spread in all directions (through a resistive material) and you would need a stronger transmitter than you would for a wire. While a fraction of a watt will send a signal for miles down a cable, you would need hunderds of watts to do the same in soil (even ideal).

At 30Hz, you cannot transmit audio, you have to very slowly transmit digital like a 300baud modem but slower. A short message could take a long time to recieve. But thats what you need to ocean wide signaling. Up to 3khz you could get some distorted audio through.

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Interesting Stuff

Post by VIRAND » Tue Jun 26, 2007 6:01 pm

Radio Waves below 22 khz:
http://www.vlf.it/
eerie!...
http://www.vlf.it/kurt/elf.html

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Post by Robert Reed » Tue Jun 26, 2007 8:53 pm

Virand
VERY interesting sites. Its almost like the birth of radio waves all over again. Almost makes one curious enogh to do a little exploration of their own.

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Post by Externet » Tue Jun 26, 2007 9:38 pm

Extraordinary place !
Thank you, Virand. Many hours of learning there.
Miguel
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