Evening Post, 13 January 1912, p 9
HOW THE SYSTEM WORKS.
Some years ago, when wireless telegraphy flashed into tho public eye as the nine hundred and ninety-ninth nine days’ wonder of a wonderful age, I attended with many other interested folk a lecture on the subject by an electrician of note.
It was a fashionable enough gathering, for wireless was new and people wanted something fresh to talk about, but I did not envy the lecturer his task. If he had been explaining the steam-engine or the motorcar or even the aeroplane it would have been comparatively easy. There is something visible and tangible and intelligible in their working. A lecture on chemistry, botany, geology, astronomy, or biology, a discourse on eugenics or an exposition of the Mendelian theory, would have been child’s play beside the Herculean task of demonstrating the principles of radiotelegraphy.
Needless to say, the lecturer failed. He began with a lot of weird diagrams on the screen, which to the average man looked like a game of noughts and crosses decorated with primitive hieroglyphics of snakes climbing poles or encircling other snakes. Doubtless to the ladies present it might have recalled the how-to-do-it illustrations of the latest fancy stitch on an up-to-date sewing machine.
And the lecturer’s language was interlarded with strange words never heard, in good society — “ions,” “farads,” “ohms” (some people wondered if there was not an “h” misplaced somewhere), “amperes,” “kilowatts” (that’s somewhere in Ireland, isn’t it?), “choke-coils” (must be the way they hang people by electricity in America!), “Leyden jars” (how nice they would be for jam or pickles!), “aerials,” “coherers,” and so forth ad lib.
The only words recognised were apparently “Marconi” and “wireless,” and those provoked inopportune applause which pained the expert. He got tired of it all and wound up the entertainment with some experiments, which at least gave the audience something for their money. They were duly edified by crackling sparks, ringing bells, exploding squibs by wireless in the further corner of the hall, and the sworn testimony of friends who put on the telephone ear-caps and heard noises in them.
But for all the knowledge of the principles of radio-telegraphy they picked up at that popular lecture, they might have been witnesses of the mysteries of the Black Art. For unless you know something of the elementary laws of electricity, you will not be able to understand wireless.
After what has been said, it seems only like courting the fate of that popular lecturer to try to explain the working of wireless in the columns of the newspaper. But the temptation is there; the subject is exceedingly fascinating, and, moreover, of much interest to New Zealand, in view of the projected establishment of wireless stations at different places in the Dominion.
Our own post office in Wellington has been operating a station with considerable success for many months now, and the sending and receiving of radio-telegrams to and from vessels at sea is a regular branch of departmental business.
We have our own investigators in radio-telegraphy, and it is quite on the cards that they may contribute to the improvement of the system in various directions themselves. Among these is Mr P.O. Spry, the City Motor Inspector, who has been a practical student of wireless telegraphy for a good many years now. He has experimented largely with home-made apparatus on different systems, and has met with most encouraging results. It is to him I owe much of the information on the subject I want to present in an intelligible form as an explanation of the working of wireless. I hope I do not misrepresent him.
To the man on the street, paradoxical as it may seem, the only visible apparatus of a wireless station is the wires. You can see them suspended between the Post Office tower, where the station is situated, and adjacent high buildings. These are the “aerials” in wireless telegraphy; from them messages are flung off, as it were, into space, and by them messages from space are received. They are, so to put it, the Cape Farewell of wireless, the first and last of it.
It requires complicated electrical apparatus to charge the aerial with the electrical energy, whose radiations are felt hundreds of miles away. It requires equally complicated apparatus to detect and receive the faint radiations from other stations hundreds of miles away. If we assume the existence of such apparatus, the phenomenon of wireless telegraphy may at the outset be more readily understood.
The aerials are loose ends flung into the air, feelers, antennae, as the wires are technically known. These are charged with electricity at enormous pressure from twenty to a hundred times the voltage of the ordinary city electric lighting circuits — as much as 50,000 volts sometimes, though Marconi in his Trans-Atlantic stations uses about 12,000.
So long as the aerial remains charged a tremendous electrical strain is imposed on the surrounding ether. The electrical energy is, as it were imprisoned in the aerial, and endeavours to burst its bonds and complete the circuit with the earth. If the electrical strain is suddenly removed, the ether, as it were, collapses, producing radiating waves, which travel with the speed of light, 186,000 miles a second.
The removal of the strain is effected by the Morse key through a system of complicated electrical apparatus, and by the same key the process is continued. The aerial is instantly recharged, the electrical strain returns, and by another depression of the key is removed, the ether collapses, and another series of waves is sent out.
By suitable apparatus these waves in the code of the Morse alphabet are detected, received, and interpreted in some far-away station perhaps hundreds of miles at sea.
It is hard to describe with sufficient clearness the machinery and apparatus employed in the transmission and receipt of wireless messages. The current is generated by dynamos, sometimes steam-driven, as in the great Marconi stations, or driven by oil engines, as in the stations designed for service in New Zsaland.
The voltage is stepped up up enormously by transformers, the primary coils of which are in the circuit broken by the Morse key. The secondary coils lead to a circuit with a high-potential condenser, consisting of large jars with tinfoil or copper plate inside and out. This condenser stores up electrical energy and imparts it through an inductance coil at a slow rate, electrically speaking, to the radiating aerials.
The current is alternating with extremely high frequency — 45,000 periods in the Marconi high power stations. Oscillations of high frequency are produced in the aerials or elevated conductors with the result that energy in the form of electric waves is radiated through space. The two circuits employed in transmission are tuned in electric resonance and groups of waves are omitted at regular, intervals in such a manner that their cumulative effect produces a clear musical note in the receiver.
The tuning is an essential part of wireless telegraphy. The length of the waves sent out depends on the capacity and inductance of the aerial and also of the frequency of the alternations. In commercial wireless telegraphy the wave lengths used are 300 and 600 metres. By varying the inductance and capacity of the elevated conductors the tuning may be adjusted.
The detection and receiving of messages is done by very delicate instruments tuned to harmonise with the transmitting apparatus. There are many forms of detector, some of which depend on the use of rare minerals for rectifying the direction of the current. The problem of receiving messages has been solved in a score of ways.
But the problem of wireless telegraphy still has its mysteries. As Commendatore Marconi, the pioneer of wireless, puts it. “Although we have — or believe we have — all the data necessary for the satisfactory production of electric waves, we are still far from possessing any very exact knowledge concerning the conditions governing the transmission of these waves through space, especially over what may be termed long distances. Although it is now perfectly easy to design, construct, and operate stations capable of satisfactory commercial working over distances up to 2500 miles, no really clear explanation has yet been given of many absolutely authenticated facts concerning these waves.” If Marconi does not know, who does?
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