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Mobile Telephone History
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Early Radio Discoveries
Over the next thirty years different inventors, including Preece and Edison, experimented with various induction schemes. You can read about many of them by clicking here (internal link). The most succesful systems were aboard trains, where a wire atop a passenger car could communicate by induction with telegraph wires strung along the track. A typical plan for that was William W. Smith's idea, contained in U. S. Pat. No. 247,127, which was granted on Sept 13, 1881. Edison, L. J. Phelps, and others came out later with improved systems. In 1888 the principle was successfully employed on 200 miles of the Lehigh Valley Railroad. Now, let's get back to true radio and Maxwell's findings, which lead to intense experimenting.
Maxwells' 1864 conclusions were distributed around the world and created a sensation. But it was not until 1888 that Professor Heinrich Hertz of Bonn, Germany, could reliably produce and detect radio waves. Before that many brushed close to detecting radio waves but did not pursue the elusive goal. The most notable were Edison and David Edward Hughes, who became the first person to take a call on a mobile telephone.
On November 22, 1875, while working on acoustical telegraphy, a science close to telephony, Thomas Alva Edison noticed unusual looking electro-magnetic sparks. Generated from a so called vibrator magnet, Edison had seen similar sparks from other eclectric equipment before and had always thought they were due to induction. Further testing ruled out induction and pointed to a new, unknown force. Although unsure of what he was observing, Edison leapt to amazing, accurate conclusions. This etheric force as he now named it, might replace wires and cables as a way to communicate. Under deadline to complete other inventions Edison did not pursue this mysterious force, although in later years he returned to consider it. Edison's vibrating magnet had in fact set up crude, oscillating electromagnetic waves, although these were too weak to detect at much distance. [Josephson]
D.E. Hughes and the first radio-telephone reception
From 1879 to 1886, London born David Hughes discovered radio waves but was told incorrectly that he had discovered no such thing. Discouraged, he pursued radio no further. But he did take the first mobile telephone call. Hughes was a talented freelance inventor who had at only 26 designed an all new printing telegraph (internal link). Like Edison and Elisha Gray he often worked under contract for Western Union. He went on to invent what many consider the first true microphone, a device that made the telephone practical, a transmitter as good as the one Edison developed.
Hughes noted many unusual electrical phenomena while experimenting on his microphone, telephone, and wireless related projects. The telephone, by the way, had been invented in 1876 and plans for constructing them had circulated around the world. Hughes noticed a clicking noise in his home built telephone each time he worked used his induction balance, a device now often used as a metal detector.
From the illustration and explanation on the previous page we know that turning current on and off to an induction coil can produce a clicking sound on another wire. It would seem then that Hughes was receiving an inductively produced sound, not a signal over radio waves. But Hughes noticed something more than just a click. In looking over the balance Hughes saw that he hadn't wired it together well, indeed, the unit was sparking at a poorly fastened wire. What would Sherlock Holmes have said? "Come, Watson, come! The game is afoot."
The spark we see isn't the radio signal, instead, it is light from energy released by excited or charged atoms between the spheres. And the spark does not indicate a single current flowing in one direction, but rather it is a set of oscillating, back and forth currents, too fast to observe.
Fixing the circuit's loose contact stopped the signal. Hughes correctly deduced that radio waves, electromagnetic, radiated emissions, were produced by the coil of wire in his induction balance and that the gap the spark raced across marked the point they radiated from. He set about making all sorts of equipment to test his hypothesis. Most ingenious, perhaps, was a clockwork transmitter that interrupted the circuit as it ticked, allowing Hughes to walk about with his telephone, now aided by a specially built receiver, to test how far each version of his equipment would send a signal.
At first Hughes transmitted signals from one room to another in his house on Great Portland Street, London. But since the greatest range there was about 60 feet, Hughes took to the streets of London with his telephone, intently listening for the clicking produced by the tick, tock of his clockwork transmitter. Ellison Hawks F.R.S., quoted and commented on Hughes' accounting, published years later in 1899:
"He obtained a greater range by setting 'the transmitter in operation and walking up and down Great Portland Street with the receiver in my hand and with the telephone to my ear.' We are not told what passers-by thought of the learned scientist, apparently wandering aimlessly about with a telephone receiver held to his ear, but doubtless they had their own ideas. Hughes found that the strength of the signals increased slightly for a distance of 60 yards and then gradually diminished until they no longer could be heard with certainty." [Hawks]
Since Hughes moved his experimenting from the lab to the field he had truly gone mobile. Although these clicks were not voice transmissions, I think it fair to credit Hughes with taking the first mobile telephone call in 1879. That's because his sparking induction coil and equipment put his signal into the radio frequency band, thus fulfilling part of our radio definition. Modulation, the act of putting intelligence onto a carrier wave such as the one he generated, would have to wait for others. This was an important first step, though, even though his clockwork mechanism signaled simply by turning the current on and off, like inductance and conductance schemes before.
Now, we can signal using a spark transmitter without a coil. This would be just like a car spark plug. When spark plugs fire up they spew electrical energy across the electromagnetic spectrum; this noise wreaks havoc in nearby radios. It's typical of all unmodulated electrical energy called, appropriately enough, RFI, for radio-frequency interference. Light dimmers, electrical saws, badly adjusted ballast in fluorescent light bulbs, dying door bell transformers, and so on, all generate RFI. If you turn the source of RFI on and off you could communicate over short distances using Morse code. But only by interfering with true radio services and causing the wrath of your neighbors. By contrast to spuriously generated electrical noise, Hughes deliberately formed electromagnetic waves which easily travelled a great distance, were tuned to more or less a specific frequency, and were picked up by a receiver designed to do just that.
Beginning in 1879 Hughes started showing his equipment and results to Royal Society (external link) members. On February 20, 1880 Hughes was sufficiently confident in his findings to arrange a demonstration before the president of the Royal Society, a Mr. Spottiswoode, and his entourage. Less knowledgeable in radio and less inquisitive than Hughes, a Professor Stokes declared that signals were not carried by radio waves but by induction. The group agreed and left after a few hours, leaving Hughes so discouraged he did not even publish the results of his work. Although he continued experimenting with radio, it was left to others to document his findings and by that time radio had passed him by.
Coils and what makes up an oscillating electromagnetic wave
The coil Hughes used raised the audio frequency signal on his line to the lower end of the radio band, providing an essential element of our radio definition. How was the frequency raised? Voice, conversations, music, and all other acoustic sounds reside in the the audio frequency band, far below the radio frequency band. Our range of hearing extends to perhaps 20,000 cycles a second, whereas the radio band starts around 100,000 cycles per second, with normal radio frequencies much higher. Let's stop right here to make a distinction between audio or acoustic signals and radio waves.
Sound waves are acoustic waves, with no electrical component. They are simply vibrations in the air, a physical pressure made by the utterance of a speaker or other sound source. Sounds in the audio and radio band both travel in waves but otherwise they are completely dissimilar. Acoustic waves are sounds made manifest by a physical distrubance, electromagnetic or radio waves are the product of radiated electrical energy.
When put on a wire a sound occupies the frequency it would normally take up if not on the wire, that is, if a normal conversation is taking place at around 500Hz, then the conversation would naturally set up at 500Hz if put on a wire. That's a simple example, of course, since the telephone system for several reasons limits this baseband or voice band channel on a telephone wire to around 300Hz to 3,000Hz.
As the diagram above show a wire laid flat exhibits only a simple electromagnetic field when current flows. But if you scrunch it together, start running dozens of feet of wire around a core, spacing each loop nearly on top of each other, well, now you've really changed the dynamics of that line. You might have 25 feet or more of wire on a five inch core.
Have you ever seen an A.M. radio antenna in an old style radio? All that wire, wrapped around a ferrite core, is designed to tune frequencies from around 560,000 cycles per second, to about 1,600,000 cycles per second. The length of the wire tries to represent the length of the radio wave itself, although in practice it may be a quarter wavelength in size or less. The closer in size your antenna comes to the size of the wavelength you want to listen to, the better your chances are of receiving it. If you took that same antenna, no core needed, and wired it into a telephone line, you will probably raise the signal on the baseband channel into the low end of the radio band.
Modern radios don't use this principle to produce a high frequency carrier wave, of course, but the point I am making is that an induction coil to produce electromagnetic radio waves was an element which distinguished Hughe's work from more primitive schemes.
So who did complete the first radio telephone call using voice? None other than Alexander Graham Bell, the man who invented the telephone and of course made the first call on a wired telephone to Thomas Watson. Bell was also first with radio, although in a way you probably wouldn't imagine.
Time out for terms!
Inductive reactance is the proper term for opposition to current flow through a coil. Resistance of a circuit and inductive reactance, both measured in Ohms, makes up impedance. The other confusing term in radio is AC.
In many radio discussions AC does not mean the alternating current that powers your appliances, rather, it means the way audio signals alternate in a wave like fashion. Huh? As we've just seen above and on the on the previous page , we need a change in current flow through a coil to get radiation. Current must go on and off to release the electromagnetic energy stored within the coil.
AC in radio means the natural alternating current of a voice signal, that is, the normal up and down waveform of the analog signal. In this case the rise and fall of a signal above a median point, that is, the top and bottom of a wave. Alternating current. Get it? A battery powered walkie talkie illustrates the difference between AC signaling current and AC power current.
A battery powered radio transmitter uses direct current to do all things. Including converting your voice, through the microphone, into a signal it can transmit. But the signal it transmits is not called a DC signal but an AC signal. That's because the radio rapidly oscillates (or alternates) the original signal. This is the needed step to get the signal high enough in the frequency band so that it will radiate from the antenna. AC, in this case, is not the power coming out of a wall outlet, it is the alternating current formed by waves of acoustical energy in the voice band converted into electrical waves by the radio circuitry.