1902 Wireless Telephone

[bobskie]

I came across this article supposedly from the Saint Louis Post-Dispatch on January 12th 1902. It states that a man discovered wireless telephony by sending signals through the ground. It's an interesting read but I personally believe some sort of trickery must have been at play here, I can't see how the concept would work. What do you think? link

[M0FYA Andy]

I recall doing some experiments as a youngster, using an audio amplifier to feed two spikes in the ground, and going some distance away with another two spikes to knock in the ground connected to a pair of headphones.
It certainly worked, although I don't think the distance attempted was more than 100 feet.

Andy

[G6Tanuki]

In the 1970s a group of us schoolkids played around with "ground communication" while we were also studying for our RAEs.

A public-address amplifier [100V line-output] connected to a pair of spades rammed into the ground about 20 yards apart gave good 'copy' on another couple-of-spades-and-a-DLR5-headset about 1/4mile away. Biggest problem was mains-hum!

I also did some experiments using a self-excited PL509 oscillator running at around 70KHz, AMed by the same 100V-line PA amp. Receiver was a CR100. With that I got nearly a mile, and no mains hum though the modulation-quality was awful [don't modulate a free-running oscillator!]

I gather that during WWI bayonets were used as 'earth' connections for ground-loop telephones in the trenches.

[n_r_muir]

In WW1 the Germans intercepted British front line telephone and Morse buzzer set communications, not necessarily by "tapping into the lines" but by inserting metal rods into the ground, some distance apart. By connecting these rods to an audio amplifier, communications could be intercepted. This was because the British field telephones were only directly connected to the switch boards by one wire, the other terminal was connected to ground via a metal rod. It was these "ground return currents" that were being intercepted and suitably amplified.

Discovery of these German "Moritz" intercept posts lead to the use of 2 wire connections for field telephones and the invention of the Fullerphone for more secure Morse transmission over wires.

Ross

[bobskie]

That's very interesting, I didn't think the ground would be conductive enough to carry signals over such a distance. It's interesting to see some of these inventions from the past that are buried in the mists of time. If this had been discovered a few years earlier perhaps we would have received radio and communicated in a very different way, at least for a time.

[Biggles]

One leg of a normal twisted pair telephone line if earthed by a fault can cause all manner of problems. Hum is one symptom even if miles away from any DNO equipment. I have seen earth faults take enough current to busy the line on auto exchanges. I suppose it all depends on ground conductivity, which seems to be pretty good where I work, much of the land being waterlogged most of the year round.
Alan.

[Herald1360]

The ground is like a 3 dimensional distributed resistor so not all of the current between the driven electrodes flows directly between them, some will spread out over a large area. Two spaced spikes some distance away will have a voltage, however small, between them. If there's a few mV and no other noise, it's enough to be useful.

[Wendymott]

Not directly connected.. forgive the "pun".. but Ground resistivity survey instruments use a 4 wire method... to detect buried walls and trenches etc, where a constant AC current is inserted in two of the probes.. and the voltage detected by the other two probes. Two fixed probes are placed at the outer edge of the survey site, one voltage and one current. The other two probes, again one voltage and one current, are moved across the suspected anonomoly .. if the object is a wall the resistance would increase, due to the lack of moisture, whereas a ditch with loose fill would be low resistance retaining more water. Its just a wien bridge really.
AC was used to minimise probe polarisation if DC was used.
We developed these instruments in the early 70's at Bradford University, and are still available today.

[emeritus]

I seem to remember that in Victorian times, someone experimentally used ground currents to communicate between the Isle of Wight and the mainland using pairs of electrodes spaced-apart by a large distance.

[Amraduk]

In the late 1950s, I was still at school when we first had a phone installed, when we still had a manual exchange, it had to be a shared service, AKA a 'party line'. An earth connection was used in conjunction with one of the legs, A for one phone and B for the other, so that the appropriate phone could be rung depending on which of the two subscribers was being called.

When the exchange was changed to an automatic one, a push button was added to the phones just above the dial, to make a call, the button was pressed to indicate which subscriber wanted to make the call and you then got dialling tone. This was again by using the earth which was connected via the button to one leg or the other. The earth continued to be used with one leg or the other for ringing the appropriate bell.

There was an occasion, when the legs got crossed over, so calls were directed to the wrong party! No doubt any calls made during that period would have also been charged to the wrong subscriber! If we had a call that was meant for the other 'party' I was able to tell them to use our phone number instead. I don't remember how long the fault lasted but I don't think it was very long.

Regards,

Dave.

[Graham G3ZVT]

Originally Posted by bobskie

I came across this article supposedly from the Saint Louis Post-Dispatch on January 12th 1902. It states that a man discovered wireless telephony by sending signals through the ground. It's an interesting read but I personally believe some sort of trickery must have been at play here, I can't see how the concept would work. What do you think? link

I certainly played around with ground communication in the early '70, but my light-beam telephone was more successful.
A similar technique to the ground telephone was used between divers and their support boats.

Graham.
G3ZVT

[Brigham]

Over short distances, the 'return' leg of a two-wire telegraph circuit has less resistance than the Earth.
Over a certain distance, the Earth return becomes the 'line of least resistance', rapidly approaching zero ohms.
The width of the Earth path is the relevant factor.

[Graham G3ZVT]

It seems that HVDC submarine interconnectors use the sea as the return path.

Single wire earth return AC power transmission is used in some parts of the world.

Graham.
G3ZVT