Monday, February 14, 2011

Radio Panorama RP8: Signaling Through the Earth

In the early eras of history, electricity was observed as a static phenomenon; that is, an electrical charge was observed for example, when amber material was rubbed with a cloth. The electrical charge remained on the surface of the amber for a period of time, and it did not dissipate immediately; that is, it was not a form of flowing electricity, but it was a stationary, or static charge.
However, when experimenters began to generate and experiment with moving, or current electricity, they discovered that a circuit was involved. In other words, it was not possible to induce a moving current of electricity through a single open wire, there had to be a return for the electricity, a circle, a circuit.
It would be suggested that the need of a closed circuit for the flow of electricity was first demonstrated at the time when Luigi Galvani in Italy joined two wires, zinc & copper, and touched the other end of each wire on the leg of a frog. This procedure made the muscles of the frog twitch. Although it was not understood clearly at the time, back in the year 1780, this experiment demonstrated the flow of electricity through a closed circuit.
Likewise, 20 years later, Alessandro Volta also in Italy, invented, developed, the battery cell. He inserted two joined wires, zinc and copper into a solution of salt water and he discovered that this created a flow of electricity, an electrical current.
During the year 1837, both Samuel Morse in the United States and Cooke & Wheatstone in England developed a telegraph system with the use of a twin wire circuit. That is, the electrical signal had to travel from the first location along a connecting wire to a second location, and back to the original location along another wire.
However, during the following year, 1838, Professor Karl von Steinheil in Munich Germany experimented with the concept of using the earth as the return segment of a telegraph circuit, thus eliminating the need for the return wire. He inserted a metal plate into the earth at each end of the telegraph circuit. He suggested that therefore it might be possible to use the earth itself as a connecting medium for the transmission of a telegraph signal, a wireless signal if you please.
When the Overland Telegraph was constructed in Australia in 1872, a single galvanized iron wire connected Darwin in the north and Adelaide in the south, a distance of nearly 2,000 miles. Each end of the wire was enabled with an earth connection.
In 1866, the dentist Mahlon Loomis, experimented with the concept of using the sky and the earth as the twin connecting media for a wireless telegraph circuit. He flew two kites, each with a spark gap and a connecting wire onto a plate in the ground, at a distance of 14 miles in the Blue Ridge Mountains in the American state of Virginia. This system worked, but he did not realize that he had succeeded in transmitting a wireless signal through the sky, not through the ground.
in 1880, Professor John Trowbridge at Harvard University in Cambridge Massachusetts experimented with the concept of transmitting wireless signals through the earth and he successfully received the university’s ticking time signals at a distance of one mile. However, he discovered that the signal strength quickly dissipated due to the fact that the signal transmitted through the earth was omnidirectional at ever widening circles.
Now when Guglielmo Marconi began his early wireless experiments in Bologna Italy, he discovered that he could transmit a wireless signal over a significant distance with the use of a spark gap transmitter and a spark gap receiver, each connected to an elevated aerial and an earth plate inserted into the ground.
Almost simultaneously, Alexander Popov in Russia developed a workable wireless system using a similar concept.
Thus it was that early wireless experimenters discovered that the earth could be used as a transmitting medium for wireless signals though it was a highly inefficient procedure. However, when wireless and then radio came to stay, the usage of an earth grounding did play an important part in the circuitry.
Another concept for the early wireless experimenter was the usage of water as a connecting medium for the transmission of intelligible signals, and that’s our story for another occasion.
(AWR Wavescan/NWS 103 via Adrian Peterson)