I usually try to stay "in the know" on this subject, have for years so I'm surprised this thread slipped under my RADAR for this long.
Through ground radio is a fascinating subject that has captivated me since I was a teen when I checked an electronics communication book out of the library in which the author discussed this topic of buried antennas and even reported that he and a friend that lived 2 blocks from each other sent and received signals through the ground that distance. One plugged the output of his guitar amp into two ground poles spaced apart by a good distance and the other guy plugged in an audio amp for a receiver into similar ground rod setup at his house and could hear the guitar.
I was fascinated by this and did a lot of research on the likes of Nathan Stubblefield's work with his wireless telephone and Heinrich Barkhausen, German Physicist who spied on allied Army field phones during WWII using two rods drove into the ground a few hundred yards apart near the trenches the field phones were being used.
I wanted to build a two way transceiver system that would allow me to talk through the ground covertly to a close friend of mine.
Long story short, I eventually accomplished this and found that it's actually quite easy and cheap to implement a system like this that will work for short ranges such as the two city block distance that that author mentioned.
I also believed and still do, that there is a way to get much longer range.
Short range is easy. I have two copper ground poles driven into the Earth behind my House on my property border that are about 3 feet deep and about 30 feet away from each other, this antenna arrangement is known as an Earth Dipole or Ground Dipole and theoretically acts like a loop antenna. A lot of research has been done on this setup and can be found online from various sources such as the VLF.it website. Those two poles are wired to 14 guage stranded that come into my upstairs Lab via a PVC conduit and hook to my transmitters which are basically audio amplifiers.
I've transmitted all kinds of different signals from strait audio like music from CD through AM modulated VLF carriers at different frequencies all the way to pulsed DC which, according to Tesla, will travel further through the ground than an AC signal.
My receivers are Homebrew ones made from TL081 OpAmps driving the LM386N-4 driving 8 Ohm speaker and are battery powered. I put these receivers into small cases with carrying handles and have switched high pass filter circuits on the front end to knock down 60 Hz power line buzz and switchable low pass filters to eliminate and auto rectification from strong AM Broadcast Band signals from booming in. The receivers are battery powered and I just connect the input through an earphone jack to two small car antenna stainless steel rods with the round balls on top so I can shove them a few inches into the ground about 5 feet apart and receive the signals coming from my transmitter. I've spent hours playing music at various levels and modulations on the transmitter and me walking around in the fields and town surrounding my house pushing those receiver rods in the ground and determining how far the signal can be picked up.
I even built two fully functional transceivers and hooked mine to two poles across the front of my House driven into the ground on either side of my porch, while I gave the other one to my neighbor across the street in front of my House with two poles in his yard and we made my first through the ground QSO years ago, it was INCREDIBLE.
So how far have I managed to get a signal through the ground? God only knows but as far as I have been able to receive one of the signals I've put in the ground with my 30 foot wide transmitting Earth Dipole was about 1 quarter of a mile.
That was transmitting a pulsed DC signal at 1 kHz that was basically a beeping beacon.
I took a 40 Volt power supply and came strait off the positive power rail to the collector of an NPN power transistor the emitter connected to one ground rod and the negative power rail to the other ground rod. The base of the transistor was driven by a 1 kHz square wave oscillator I made with a NE555P timer ship. This put out a full 40 volt pulsed DC that could be heard as a loud beep on the receivers. It was so strong in my yard I could actually hear it over my House intercom somehow bleeding through and even on my Home phone
when I picked it up to check. I didn't even have to stick both ground rods into the ground for my receiver to pick it up only one and holding the other in my hand as I was about to plug it in, just getting it close to the ground it was already coming out the speaker. As I moved further out into the fields after about 100 yards I had to use both rods and turn up the gain and volume incrementally as I walked further and farther away. The signal remained strong out to 1/4 where it faded into the noise.
I did many, many experiments over the years. My neighbor lost interest but I still have the two working transceivers which are just basically push to talk audio intercoms connected to ground poles instead of a speaker cable. They put out about 170 volts peak to peak audio signal.
One thing you have to be careful of when transmitting is the transmitters have to be COMPLETELY isolated from the House neutral and ground wire otherwise instead of the ground current going between the two poles the signal will also radiate from the House and power pole ground rods and severely disrupt the current pattern which destroys the performance of the earth Dipole and the reception of the signal, so everything has to be powered from batteries, or everything in the transmission system including my laptop computer audio source has to be powered from an Isolation transformer to remove the ground reference (which is the method I usually use).
My old ground rods and wires coming into my lab are still there and yesterday while I was monitoring the VLF spectrum with them and my Spectrum Lab (DL4YHF's audio spectrum analyzer) free software for VLF monitoring. I decided to transmit again and see how much clearer the audio would come in using the Spectrum Lab software's Natural Radio quick setting that has a sophisticated filter that completely eliminates the 60Hz power line buzz and nearly all of its harmonics (it's AMAZING) and lets you listen to the whole audio range of ELF/VLF spectrum buzz free that I have been enjoying for a few days now.
So I ran outside and stuck two small probes in the ground about 20 feet apart and drove them a few inches into the ground. These are about thirty feet from the old transmitting poles that I was using for receive poles yesterday. I then fed a 12 Volt peak to peak audio signal, as verified by my oscilloscope, to those poles and played some music from my laptop. The clarity and strength was AMAZING! Then I used my ol' trusty HP 4204A oscillator to drive some clean sine waves and various frequencies, being sure the output stayed at exactly 12 Volts peak to peak and put a DMM with high frequency Ammeter inline so I could see how mush current was flowing between the ground rods and see how much power was being put into the ground.
At 3 kHz - 20.5 mA = 86mW.
At 7kHz - 22.0 mA = 93mW.
at 150kHz - 31.0 mA = 131mW.
So as I went up in frequency, the rods drew more current which prove the capacitive effect that others have observed using the earth dipole to transmit ELF/VLF signals.
Once years ago the farmer who owns the land behind my House let me put a 3rd ground rod FAR down his fence line and run another wire zip tied to that fence to my lab. It was the furthest I've ever transmitted a strait audio signal through the ground, nearly a quarter a mile and the poles were about half that distance apart from each other. I should have tried the 40 volts DC pulse circuit then, no telling how far it would have went, but I wanted to send audio only, not do any Morse Code work. I'm still not finished with my work on this yet. I have a tube amplifier audio output transformer coming that I intend to use to step up a decent sized audio amp output to a kilovolt or so and hopefully put some real power into the ground and once again see how far I can get the signal to go.
I've done so much experimentation on this subject but would have to spend hours trying to explain everything I've learned. My experiments have taught me:
Suffice it to say transmitting audio and VLF/ELF through the ground using ground conduction with ground rods (Earth Dipole) actually works and will transmit about twice as far as the poles are apart, using 170 volts or less peak to peak audio signals. The farther you spread the poles from each other, the further the signal will go. The Earth Dipole is DIRECTIONAL especially when receiving! You must line up the receiving poles facing the direction of the incoming signal from the transmitter. If you plug the receiving poles into the ground parallel with the transmitting poles it's as if the signal wave strikes both poles at the same time and there is no voltage potential difference for the OpAmps to amplify. The signal coming from the transmit rods is kind of the opposite, the signals radiates out the sides the strongest but also 100's of yards in the direction the poles are lined up with.
There is much more experimentation and documentation that needs to be done.
placing two conductive rods into the ground and putting DC or AC voltage to them will cause current to flow between those rods but the current also spreads out a long distance surrounding the rods.
There may be Eddy currents involved at very long distances and other factors that could cause really long range to be viable. I hope someone else out there will also want to do some work with this subject. I'll report back if and when I learn anything else. -73's fellow ground radio and radio enthusiasts.
