HISTORY OF THE RADIO

 
 
 
 

 

 

 

  

A RETROSPECTIVE GLANCE

With the telegraph and the telephone, the man already could communicate to great distances, even through the seas thanks to underwater cables, but only between the points in which these cables arrived. But still the boats, vehicles, zones little populated, etc. were isolated.

The overcoming to these difficulties began if possible with a series of discoveries:

During the development of the electricity, they had appeared several theories to explain many classes of electrical phenomena, creia at the outset that the electrical action happened remote on the different bodies that thus could experience it.

But the discovery of the electrical current motivated that doubts surgan on that one mysterious action. Faraday did not believe in that action adistancia, and in 1835, when writing on a perfected form of voltaic battery, he observed that the electrical current propagated as if discreet particles of electricity existed.

The ideas of Faraday did not fall in the forgetfulness and his compatriot Maxwell gathered them later thirty years, to translate them to the mathematical language, drawing from them the most transcendental conclusions.

James Clerk Maxwell in 1867 presented its electromagnetic theory (Electricity and Magnetism) to the Real Sociedad of London. This theory, obtained by pure mathematical calculation, predicted the possibility of creating electromagnetic waves and their propagation in the space. These waves would propagate by the space at the speed of 300 thousand kilometers per second.

The first attempts to confirm this theory were realised by professor Fitzgerald, of Dublin, but they did not give practical results until, the German physicist Hertz, who did not know the investigations of Fitzgerald, undertook the same task.

The German Heinrich Hertz in 1887, confirmed the theory of Maxwel experimentally, broadcasting and studying the electromagnetic waves with his oscillator and a resonator, realised the first transmission without threads, than from then hertzian waveses would be denominated in their honor.

This experiment served to confirm the ideas of Maxwell and let glimpse the possibility of producing electrical waves at a distance and of catching them by means of suitable equipment. It was, then, the first attempt of radio communication by means of the electromagnetic waves, and the first practical result of which there was to germinate all the series of experiments.

The discovery of Hertz, although allowed to verify the existence of the electromagnetic waves and their parcidas properties to those of the light waves, thus confirming shiningly the theory of Maxwell, did not have immediate practical results, because the resonator, that revealed the presence of the waves, only could work to very short distance of equipment that produced them.

In 1884 Calzecchi Onesti it discovered the electrical conductibility that they take filings from iron in the presence of the electromagnetic waves, that is of the hertzian waveses

The Branly French, in 1890, I construct its primitive choesor (coherer), that allowed to verify the presence of broadcast waves, that is to say to detect them, and that it would be used by all the investigators who then wanted the communication without threads (without cables).

The coherer of Branly consists of a crystal tube within which are iron filings, something tight, between two metallic poles that communicate with an electrical battery. The resistance of filings too much is lifted so that pass the current of the battery, but in the presence of a hertzian waves this conductibility increases and the current that happens through equipment can notice making sound an electric bell.

With equipment of Branly the hertzian waveses to much more considerable distances could attract that with the resonator of Hertz, but, anyway, could not still obtain practical applications. The Popov Russian believed to find in the tube of Branly sensible equipment to reveal the march of storms, because the electrical unloadings of stormy clouds bring about the wave form, able to be revealed by the coherer.

The Popov Russian (1859-1905) found the best system to radiate (to send) and to catch the waves: the antenna, constituted by metallic thread. 

After perfecting this equipment, Popov added to the receiving system an extended metallic thread in vertical sense, so that, when rising in the atmosphere, he could catch better the electrical oscillations. This thread was united by one of its ends to one of the poles of the coherer, whereas the other end communicated with earth and thus any difference of potential that settled down between these poles, caused by the passage of an electromagnetic wave coming from stormy clouds, made sound the timbre of equipment, whose more or less frequent peal gave idea of the march of the storm.

In this way it was born the first antenna, call thus because, to maintain the metallic thread devised by Popov, a support of aspect similar to the masts or antennas of the ships had to be used.

The 24 of March of 1896 I realise the first signal communications without threads.

These first transmissions were constituted by simple impulses, obtained by means of powerful electrical unloadings of current stored in condensers or bottles of Leyden. A turn of conductive wire, located to few meters of the unloading, produced a smaller unloading between its open ends.

The oscillator of Hertz, the detector of Branly and the antenna of Popov was, then, the three indispensable elements to establish a radio communication system, but it was necessary also to constitute a set that could work surely to have commercial applications.

Nobody had been able to obtain it, until in 1895 Marconi realised definitive experiments that provided the inventor title to him of the radio communication.

This phenomenon that began to show the electrical resonance was studied by Marconi, who in Bologna (Italy) in 1896 and just by 20 years of age secured his first practical official notices.

Using a vertical wire or “antenna” instead of cut ring and using a “detector” or equipment that allowed to discover very weak signals, soon it managed to contact until distances of 2400 M.s

Gradually it was increasing the reach of his transmissions, until in 1896 it asked for and it obtained the first patent of a system of wireless telegraphy.

Guillermo Marconi at the time of his first
experiments and their primitive emitter of sparks.

The used wavelength was located over 200 meters, which forced to use antennas of colossal dimensions. The receiver based its operation on the denominated coherer. Brandley and Lodge were two of their main perfeccionadores. In essence, the coherer was constituted by a glass tube, plenty of iron filings, which in the presence of a signal of high frequency, coming from the antenna, became driver and allowed the passage of a current that drove a timbre. When the coherer disappeared the current continued leading, reason why a blow had to occur him so that it was deactivated. These details give an idea of the difficulties with that were the investigators of that one then. 

One of the receivers used by Marconi, we can appreciate
“antenna”, the “coherer”, the “headsets” and the batteries.


In 1897, the English O.J. Lodge invented the syntony system, that allows to use the same receiver to receive different emissions.

In 1897, using a transmitter formed by a great induction coil and lifting the transmitting antennas and receiving with the help of kites (I commit), it increased the reach of the equipment to 14.5 km Also demonstrated that the transmission could be on the sea, establishing the communication between two boats of Italian navy military, to distances of 19 km the previous figure gives an idea us of his receiver.

The first contact by radio in France took place in 1898 between Torre Eiffel and Pantheon (4 km), in Paris.

In the 1899 investigator and inventor Guillermo Marconi it managed again to send a message by radio through the English Channel being united Dover with Wimereux (46 km).  

It is in this 1899, that happened the first demonstration of the value of the communications by radio to give but security to the trips in the sea, when the crew of boat “R.F. Mathews” could be saved after the shock of the boat with a light, thanks to the call of help by radiotelegraphy.

Transmitting antenna installed by Marconi in Poldhu

But in fact it is possible to be shelp that the Era of Telegrafía without Threads began a crude day, 12 of December of 1901, to the 12:30 p.m. and after lifting the receiving antenna with globes and kites up to 120 meters. of height, in some large cabins left in San Juan de Terranova (Canada) where Marconi helped by the Srs. Paget and Kemp, was able to catch a series of three points, letter S of the Morse code, a signal that finished crossing the 3,600 kilometers that separated Marconi of (Poldhu) Cornwall, in Great Britain (England). This signal was the culmination of many years of experimentation.

After the transatlantic event of Marconi in 1901, in the United States a vertiginous development in the self-construction and experimentation of equipment TSF is registered (it telegraphs without threads). 

Towards the year of 1900 they began to use the CRYSTAL detectors OF GALENA for the detection replacing the Branly coherer, the soft sensible, but much more even unstable era.

The galena crystal detector, allows the passage of the current in a single
direction, precursor of the semiconductors.

In 1904, the English J.A. Fleming contributed to the radio the first type of emptiness valve, the diode, that aside from other applications allowed to replace with advantage the troublesome detector of galena, which was continued utilzando in small receivers until the Fifties.

Valve of Fleming used as detector

With the invention in 1905 of the lamp triode (also called “audion”) by the American - the Lees De Forest, already could be amplified the electrical signals used in radio and to generate waves that were not tipsy as until then.

Valve “Audion” invented by Of Forest in 1905

With tension of only some hundredth of volts it was possible to obtain a signal of continuous or maintained transmission, which annulled the transmitters of sparks quickly. But it is more, the continuous signal easily it was modulated by carbon microphones, of the type who still is used commonly in the telephones nowadays, and allowed the voice transmission.

It was this same Dr. Lee DeForest that gave to beginning to the first radio transmissions of music and voice, using the bulb of his invention to generate electromagnetic waves, instead of the sparks.  Their transmissions from their house in California were rather experimental until finally, in 1920, the Westinhouse Electric and Manufacturing Co., established in Pittsburgh the first commercial radiofusora station: good well-known “KDKA”.

In this way radiotelegraphy took step to the radiotelephony, that would be an immense field of possibilities to the great human adventure in the communications.

Purchase constructed and ready experiments to use

More Experiments