How does wireless telegraph work

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. How did wireless telegraphy reach so far? Ask Question. Asked 4 years, 10 months ago. Active 4 years, 9 months ago. Viewed 5k times.

And would these pulses still travel that far today with the same equipment? InterLinked InterLinked 2 2 silver badges 15 15 bronze badges. Add a comment. Active Oldest Votes. The transmitter power is only 20 watts but the biggest thing on it was the parabolic dish: - And doesn't this mean that there couldn't have been very many people using the systems, since operators within hundreds of miles would all be jamming the airwaves? This was indeed a big problem and there was a famous transmission from RMS Titanic that suggested that SS Californian should "shut-up" because it was blocking a transmission from Cape race on the Canada coast: - Titanic's on-duty wireless operator, Jack Phillips, was busy clearing a backlog of passengers' messages with the wireless station at Cape Race, Newfoundland, miles 1, km away, at the time.

Andy aka Andy aka k 21 21 gold badges silver badges bronze badges. At foot high, the line of sight is only about 20 miles and clearly Titanic could transmit and successfully be received at around miles during day time. Other than the ionosphere, lower frequencies don't actually transmit any further than higher frequencies.

As author of the answer I get notifications and I'l also interested in his response. Power levels of 5 mW are actually used for intercontinental contacts. Usually, such low levels are not used for telegraphy.

Instead, digital modes with very high level of error correction coding are used. Furthermore, if you look up how digital modulations work, you'll see that many receivers use the "integrate and dump" technique.

Received signal strength there depends on the bandwidth and the symbol interval. By using extremely low bandwidths and very long symbol intervals, you can make up for that.

At 1MHz, link loss is So let's say 10, km and therefore link loss is With 0 dBm 1 mW , receive power is Throw in some antenna gain and nearly every day is a good day: electronics. Show 19 more comments. The main transmitter was a rotary spark design, powered by a 5 kW motor alternator, fed from the ship's lighting circuit A spark gap transmitter is the simplest possible form of radio transmitter, modulated with on-off keying morse code. Back then there weren't really any rules.

We might find, in a certain number of the attempts just mentioned, a partial employment of these phenomena. Lindsay, for instance, in his project of communication across the sea, attributed to them a considerable role. These phenomena even permitted a true telegraphy without intermediary wire between the transmitter and the receiver, at very restricted distances, it is true, but in peculiarly interesting conditions.

It is, in fact, owing to them that C. Brown, and later Edison and Gilliland, succeeded in establishing communications with trains in motion. Mr Willoughby S. Smith and Mr Charles A. Stevenson also undertook experiments during the last twenty years, in which they used induction, but the most remarkable attempts are perhaps those of Professor Emile Rathenau.

With the assistance of Professor Rubens and of Herr W. Rathenau, this physicist effected, at the request of the German Ministry of Marine, a series of researches which enabled him, by means of a compound system of conduction and induction by alternating currents, to obtain clear and regular communications at a distance of four kilometres. Among the precursors also should be mentioned Graham Bell; the inventor of the telephone thought of employing his admirable apparatus as a receiver of induction phenomena transmitted from a distance; Edison, Herr Sacher of Vienna, M.

Henry Dufour of Lausanne, and Professor Trowbridge of Boston, also made interesting attempts in the same direction. In all these experiments occurs the idea of employing an oscillating current. Moreover, it was known for a long time since, in , the great American physicist Henry proved that the discharges from a Leyden jar in the attic of his house caused sparks in a metallic circuit on the ground floor—that a flux which varies rapidly and periodically is much more efficacious than a simple flux, which latter can only produce at a distance a phenomenon of slight intensity.

This idea of the oscillating current was closely akin to that which was at last to lead to an entirely satisfactory solution: that is, to a solution which is founded on the properties of electric waves.

Having thus got to the threshold of the definitive edifice, the historian, who has conducted his readers over the two parallel routes which have just been marked out, will be brought to ask himself whether he has been a sufficiently faithful guide and has not omitted to draw attention to all essential points in the regions passed through.

Ought we not to place by the side, or perhaps in front, of the authors who have devised the practical appliances, those scholars who have constructed the theories and realised the laboratory experiments of which, after all, the apparatus are only the immediate applications? If we speak of the propagation of a current in a material medium, can one forget the names of Fourier and of Ohm , who established by theoretical considerations the laws which preside over this propagation?

When one looks at the phenomena of induction, would it not be just to remember that Arago foresaw them, and that Michael Faraday discovered them? It would be a delicate, and also a rather puerile task, to class men of genius in order of merit. The merit of an inventor like Edison and that of a theorist like Clerk Maxwell have no common measure, and mankind is indebted for its great progress to the one as much as to the other.

Before relating how success attended the efforts to utilise electric waves for the transmission of signals, we cannot without ingratitude pass over in silence the theoretical speculations and the work of pure science which led to the knowledge of these waves.

It would therefore be just, without going further back than Faraday, to say how that illustrious physicist drew attention to the part taken by insulating media in electrical phenomena, and to insist also on the admirable memoirs in which for the first time Clerk Maxwell made a solid bridge between those two great chapters of Physics, optics and electricity, which till then had been independent of each other.

And no doubt it would be impossible not to evoke the memory of those who, by establishing, on the other hand, the solid and magnificent structure of physical optics, and proving by their immortal works the undulatory nature of light, prepared from the opposite direction the future unity. In the history of the applications of electrical undulations, the names of Young, Fresnel, Fizeau, and Foucault must be inscribed; without these scholars, the assimilation between electrical and luminous phenomena which they discovered and studied would evidently have been impossible.

Since there is an absolute identity of nature between the electric and the luminous waves, we should, in all justice, also consider as precursors those who devised the first luminous telegraphs. Claude Chappe incontestably effected wireless telegraphy, thanks to the luminous ether, and men, such as Colonel Mangin, who perfected optical telegraphy, indirectly suggested certain improvements lately introduced into the present method.

But the physicist whose work should most of all be put in evidence is, without fear of contradiction, Heinrich Hertz. It was he who demonstrated irrefutably, by experiments now classic, that an electric discharge produces an undulatory disturbance in the ether contained in the insulating media in its neighbourhood; it was he who, as a profound theorist, a clever mathematician, and an experimenter of prodigious dexterity, made known the mechanism of the production, and fully elucidated that of the propagation of these electromagnetic waves.

He must naturally himself have thought that his discoveries might be applied to the transmission of signals. It would appear, however, that when interrogated by a Munich engineer named Huber as to the possibility of utilising the waves for transmissions by telephone, he answered in the negative, and dwelt on certain considerations relative to the difference between the periods of sounds and those of electrical vibrations.

This answer does not allow us to judge what might have happened, had not a cruel death carried off in , at the age of thirty-five, the great and unfortunate physicist. We might also find in certain works earlier than the experiments of Hertz attempts at transmission in which, unconsciously no doubt, phenomena were already set in operation which would, at this day, be classed as electric oscillations.

It is allowable no doubt, not to speak of an American quack, Mahlon Loomis , who, according to Mr Story, patented in a project of communication in which he utilised the Rocky Mountains on one side and Mont Blanc on the other, as gigantic antennae to establish communication across the Atlantic; but we cannot pass over in silence the very remarkable researches of the American Professor Dolbear , who showed, at the electrical exhibition of Philadelphia in , a set of apparatus enabling signals to be transmitted at a distance, which he described as "an exceptional application of the principles of electrostatic induction.

Place should also be made for a well-known inventor, David E. Hughes , who from to followed up some very curious experiments in which also these oscillations certainly played a considerable part. It was this physicist who invented the microphone, and thus, in another way, drew attention to the variations of contact resistance, a phenomenon not far from that produced in the radio-conductors of Branly, which are important organs in the Marconi system.

Unfortunately, fatigued and in ill-health, Hughes ceased his researches at the moment perhaps when they would have given him final results. In an order of ideas different in appearance, but closely linked at bottom with the one just mentioned, must be recalled the discovery of radiophony in by Graham Bell, which was foreshadowed in by C.

A luminous ray falling on a selenium cell produces a variation of electric resistance, thanks to which a sound signal can be transmitted by light. That delicate instrument the radiophone, constructed on this principle, has wide analogies with the apparatus of to-day. Starting from the experiments of Hertz, the history of wireless telegraphy almost merges into that of the researches on electrical waves.

All the progress realised in the manner of producing and receiving these waves necessarily helped to give rise to the application already indicated. The experiments of Hertz, after being checked in every laboratory, and having entered into the strong domain of our most certain knowledge, were about to yield the expected fruit.

It was Professor R. Threlfall who seems to have been the first to clearly propose, in , the application of the Hertzian waves to telegraphy, but it was certainly Sir W.

Crookes who, in a very remarkable article in the Fortnightly Review of February , pointed out very clearly the road to be followed.

He even showed in what conditions the Morse receiver might be applied to the new system of telegraphy. About the same period an American physicist, well known by his celebrated experiments on high frequency currents and experiments, too, which are not unconnected with those on electric oscillations, M.

Tesla, demonstrated that these oscillations could be transmitted to more considerable distances by making use of two vertical antennae, terminated by large conductors. The new mode of transmission had to compete with existing cable networks.

Marconi sold his earliest systems to lighthouses and ships, which could not access the cable network and yet had most need of rapid communication. Communication between ship and shore was by Morse code, as it was for conventional telegraphy. The equipment only transmitted messages for about miles in daylight, although that figure doubled or tripled after dark thanks to the refraction of long-wave radiation in the ionosphere.

At this time, wireless operators worked for the Marconi company and as well as communicating with other ships, they also relayed passenger messages—the new technology was something of a fashionable novelty, and first-class passengers would have enjoyed being able to send messages ashore. Titanic was fitted out with some of the best wireless equipment available. But there was not yet an established practice of keeping a clear channel for emergency communications.

This early wireless telegraphy wasn't like calling a telephone, with the ability to speak to one person directly—instead, the channels were open to everyone at the same time. Since Titanic's wireless operators were transmitting over the same frequency as other ships, and the channels were jammed with passenger communications, several ice warnings from other vessels were either missed or ignored. If this wasn't enough, on most ships there was only a single wireless operator, who worked a long shift and then closed down for the night.

But as Titanic collided with an iceberg in calm seas on the night of 14 April , Harold Cottam, operator on nearby Cunard liner Carpathia, was still awake. He was in a position to receive the first distress signal from Titanic, sent by senior wireless operator Jack Phillips.

The International Radiotelegraphic Convention, signed in , had agreed on SOS—three dots, three dashes, three dots in Morse code—as the international distress signal. The Convention had come into force in , but 'CQD', the Marconi Company's distress signal, was still widely used at the time of Titanic's voyage, including by Jack Phillips. For two hours on Titanic, Phillips and assistant operator Harold Bride continued to send out a stream of distress signals and messages that were picked up by other vessels.

The Royal Flying Corps began research into how wireless telegraphy could be used to help home-defence aircraft during German bombing raids. In the RFC developed a lightweight aircraft receiver and a Marconi half-kilowatt ground transmitter.

These transmitters were located on aerodromes in raid-threatened areas. The aircraft receiver was tuned in advance, and the pilot had to unreel a ft. Trials started in May and pilots reported that signals were clearly heard up to ten miles but at longer distances they weakened. Further adjustments were made and by November clear signals could be heard over twenty miles. Pilots could now be informed about enemy aircraft movements and therefore had a far better chance of successfully reaching them before they dropped its bombs on Britain.

Fighters were put on readiness at Four pilots briefly saw bombers, which quickly vanished. Two pilots, Oswell and Lucas, flying BE. Oswald followed a Gotha flying at 11, ft.