Damped wave

Marconi's image on a postage stamp from Moldova

Generates simplified sketch of an arc transmitter, the undamped waves

The term damped (English: damped wave), also damped wave, is a historical name of Telecommunications, for a special form of electromagnetic waves, such as arise in the first working method of wireless radio transmission. Was used this method exclusively for the wireless transmission of short or long radio signals, the Morse code. A transmission of sound was generated, the damped waves with the apparatus is not possible.

Function

Sending, the emission of the transmit power takes place at the earliest method of wireless communication with the discharge of the transmitting capacitor by two reactions:

• A spark gap which is formed between the electrodes and
• A bang

Due to the spark gap and the loud bang bang the name radio stations received this transmission method, (English: spark -gap transmitter). Its principle is based on a breadboard with a spark coil, the oscillator from Hertz, with which the physicist Heinrich Hertz, the predicted by James Clerk Maxwell, electromagnetic wave | electromagnetic waves proved and for the first time over a distance of 10 m, wirelessly sent.

The capacitor comprises two electrodes, is one pole with which one end of an induction coil connected to a wire in which a first "first -half of a circuit " is formed. From still free second pole, a wire does not now but at the coil but to an electrode in the form of a metal ball. Also, the wire from the other coil end leads are still free to just such a sphere with the same electrode, which is the other a few inches over. This results in the "second half" of, but with the above, the short straight line between the electrodes, the open circuit. From the top, looking from the perspective plan view, has the circuit so, symbolically, the shape of the letter C.

Now, when the capacitor is charged again by a short to and disconnection of a voltage source, the capacitor discharges through a spark which jumps between the two balls. Since the discharge current flows in advance on one side by the coil, it creates an electromagnetic wave, the round is radiated.

Disadvantages

In order not only a einzeles, but to be able to send multiple characters, the capacitor must be charged and discharged repeatedly. This creates the sequence: Power source switch - Switch off power source - capacitor charges up, apparatus sends - capacitor is discharged - switch power source - Switch off power source - capacitor charges up, apparatus sends - capacitor is discharged. The switch on the power source happens - in simple terms, on the Morse key. If pressed briefly created the Morse point at longer pressing - the bottom line.

These sequences of repeating the charging and discharging, which always occurred in succession, so often made ​​, how many characters are to be transferred. On the one hand it created a waveform with varying gradually increasing increasing and decreasing amplitude and sudden emergent break.

The second striking at this waveform was that they were in the no regulation of the transmission frequency is possible at the transmitter still radiated a very wide bandwidth. The consequence of these disorders means that during the transmission process, in the neighborhood no other stations more simultaneously, for example of another radio operator, was able to work. Like, not even a parallel responses of the receiving station was possible.

Pop radio stations - first vorgefürt independently, by David Edward Hughes ( 1893) and Guglielmo Marconi ( 1895), as well as the Next escaped lungs to the impact, or the clear radio transmitter that could not be solved as the central problem, therefore, were in the English-speaking world as " dirty" ( engl.: dirty ) refers.

By this damped signal of the spark transmitter they were practical only usable for transmitting messages in Morse code telegraphy. Despite the range records Marconi, as crossing the Atlantic in 1901, their era ended in wireless telegraphy to 1920. Damped waves were designated emission from the 1938 " International Telecommunications Union " as " Class B" and de facto prohibited. An example of the present, which problems represent broadband waves for the rest of the message traffic, such as radio astronomy, ultra-wideband waves (UWB ). While they are with less power, such as the historical waves radiated, the scattering of UWB is still at about 500 megahertz.

Successor

Already at the turn of the century was followed by experiments in order to produce the counterpart in the historical sense, the undamped waves. The first step was to replace an electrode through technical coal, as for example, Nikola Tesla did. The then fully developed channels including sound transmission principle, the useful, undamped waves allowed for the first time, was Valdemar Poulsen arc transmitter of 1904 and later in 1905 by Reginald Fessenden presented machines transmitter.