Arc converter

The arc transmitter, also called Poulsen transmitter in its mature form after its inventor, was used for message transmission in the long wave range and uses the negative differential resistance of an electric arc to generate oscillations.

Arc transmitters were used in the early 20th century until the late 1920s.

Development

At the time of initial development of arc transmitters already exist, the radio station of the type Marconi ( pop radio transmitter ) and machine stations. Disadvantages of this technique were:

Nicola Tesla and Reginald Fessenden, the Canadian engineer therefore tried as the first generation of undamped waves with carbon electrodes, which they put in DC coil, radio transmitters instead of the spark gap. However, neither the frequency nor the energy of the vibrations produced high enough for wireless telegraphy and telephony. Also, the Englishman William Duddell could not meet with his working after the arc method with carbon electrodes "singing arc" the conditions for wireless telegraphy in 1900. He fed the arc over inductors with DC and turned a resonant circuit of a coil and capacitor after.

Only the Dane Valdemar Poulsen succeeded in 1902 by the basic circuit of Duddell with an arc transmitter RF undamped oscillations of sufficient frequency and energy to produce. He used an anode made of copper, and a cathode of carbon. The cathode was rotated slowly and was automatically tracked to a distance of 3-5 mm, so as to achieve an even burn. For the proper operation of the station a good cooling and deionization of the space between the electrodes were necessary. For this, the copper anode and the " flame chamber " were cooled with water and a transverse to the flame very strong magnetic field " blew" the ions from the arc gap. In addition, the arc burning in a hydrogen atmosphere. With this system have been achieved undamped waves with frequencies up to 250 kHz (1200 m). 1904 Poulsen was his system of arc oscillator for undamped waves " Poulsen lamp ", patented in 15 countries.

Construction

The upper portion with the strong cooling fins comprising the combustion chamber with the two horizontally arranged electrodes. These are brought together by a short visible right lever to ignite the burning process. The two large coils provide the horizontal magnetic field. The visible under the lever motor rotates the cathode from coal. The hydrogen-containing atmosphere was initially achieved by the fact that hydrogen was passed through the combustion chamber. From 1906, a kind of wick oiler was placed over the combustion chamber, the one to two drops of alcohol per second was for a 1 kW transmitter into the chamber and allowed to evaporate there.

Benefits

The transmitter emits the arc compared to the damped oscillations of the pop radio station from a much narrower frequency band, and very little by-products and harmonics. Thus were obtained in the same transmission performance significantly greater ranges and could accommodate in a frequency band up to five times at stations. On the other hand, the narrow-band emission at the receiver side was not so easy to vote and audible only at a very specific point. For the radio traffic between two stations was needed now more accurate frequency arrangements.

Technical adjustment

To use the new type of transmitter for the wireless telegraphy were still some difficulties to deal with. In the unaccented telegraphy (A1 ) keyed undamped transmitter were not audible with the usual detector receivers, only a small tick sound at the beginning of the Morse code was close to a transmitter. Poulsen and his associate PO Pedersen developed a novel detector: A battery - powered or spring Summer delivered the rhythm of the received high frequency audible sound, such circuits were called " Tikker " or " grinder ".

The problem described here, which of course occurred machinery and later at the tube stations even when the led to the heterodyne reception, 1902 by Reginald Fessenden (Canada) and 1905 Robert Goldschmidt (Belgium ) has already been covered, but with the available (often mechanical was ) means not yet be reliably performed. It was only in 1913 succeeded Alexander Meissner ( Telefunken ) with a circuit with love tube (after Robert von Lieben ) the first proper feedback channels.

Another problem was the keying of the transmitter Poulsen dar. Since he needs a few seconds after each start until he swings stable, it can not be palpated in its primary circuit. As a solution we came forward to change by the Morsetastung the resonant circuit coil and thus the transmit frequency by 1 to 5% ( FSK mode ). In the receiving apparatus was heard the second ( gated ) frequency with the message; The first frequency with the "negative" Morse was at that time not to be used for message delivery. The modulation of the Poulsen transmitter with speech or music presented difficulties. The microphone must be connected in series with the antenna in high transmission power water-cooled multiple microphones were used to avoid overloading. This, however, was a remote Discuss the transmitter by a remote microphone not possible.

It was not until 1913 could this problem by using a telephony throttle ( after its inventor Leo Pungs - Fa Lorenz - also called " Pungs choke " ) are satisfactorily resolved between the transmitter and the earth. This new component ( it operates on the transducer principle) brought about by means of three windings on a three -legged iron core having only 1% of the antenna performance, the keying modulation and the high frequency current.

First transmitter

1904 Poulsen presented a connection between Lyngby and Copenhagen ( 15 kilometers ) and two years later, over 270 km between Lyngby and Esbjerg ago. In order to test all possibilities, international connections were necessary. Negotiations, inter alia, with Telefunken failed. Poulsen has founded with English investors, the " Amalgamated Radio Telegraph Company Ltd.. " Based in London. Even in 1906 there were radio links more than 900 km between Denmark and Cullercoats and over 1500 km between Denmark and Knockroe in Ireland. The station Knockroe was provided for further experiments in profit- promising radio operation with arc transmitters across the Atlantic. But nothing came, in 1907, the English went bankrupt donors. The " Amalgamated " was to have dissolved without a single transaction completed.

Then sold Poulsen 1908, the rights to his invention. In Germany the company C. Lorenz acquired the patents and was able to sell in the next few years in the army telegraphy stations with capacities between 1.5 and 4 kW for fixed transmitters. The Navy showed interest and acquired by Lorenz Poulsen transmitter with power up to 6 kW for use on large ships. These systems have been equipped since 1910 gradually with telephony additives. In German coast stations a 4 -kW arc transmitter for telegraphy was built only in northern dike in 1911, from 1912, there were also attempts telephony. In German trading or passenger ships arc transmitters have not been used, at least there are no reliable reports about it. Lorenz built in 1914 in Königsberg, and poses major stations with Poulsen stations.

Well received was the arc stations in the United States. Even during the 1904 World's Fair in St. Louis Poulsen had campaigned for his invention and sought investors. Cyril F. Elwell purchased in 1909 in Copenhagen, Poulsen rights for the United States and also bought the same one transmitter ( 100 watts) of Poulsen. By 1912, Elwell built 14 wireless systems with which the large cities were connected on the west coast of the USA and further east into the country ( including the following: San Francisco, Portland, Seattle, Salt Lake City). Dumping prices he competed successfully with the traditional wired intelligence services.

The U.S. Navy showed interest and initially ordered a 100 kW transmitter. For the realization of this project, Elwell took the engineer Leonard Fuller on board. With its ability to construct transmitters succeeded with several hundred kilowatts of primary power. The Navy built during the First World War on a world-wide radio network with Poulsen stations: Larger naval bases such as San Francisco and Hawaii were the now proven technology with powers of several hundred kilowatts. All major Navy ships were equipped with transmitters Poulsen small to medium capacity.

Worldwide arc transmitters were built with primary outputs of 100 kW and considerably higher: for example, in England (Portsmouth ), Greece ( Thessaloniki ) and Egypt (Cairo ). In France Elwell built 1915/16 major stations on the Eiffel Tower, in Nantes and Lyon. The French Navy since 1908 arc transmitters worked (range 120 to 160 km). Is powered by Poulsenlampe transmitter was near Bordeaux, the RF power was 1000 kW. One of seven broadcasting frequencies between 12.8 kHz and 21.7 kHz could be selectively switched. The transmitter weighed 80 tons, most of it stuck in the electromagnet. The antenna covered - to 8 poles in 250 m height hanging - a well- grounded area of 1200 m × 400 m from.

Radio station Malabar

Probably the strongest arc transmitter according to the Valdemar Poulsen system built the Dutchman Cornelius de Groot 1922/23, in Malabar (Java / Indonesia today ). They opted for the technique of arc transmitter, because all components needed for the country could be produced even. With a primary power input of 2400 kW transmitter was over a distance of 11,500 km in the connection with the Dutch wholesale station in Kootwijk ( point-to -point traffic ).

The station with the call sign PKX adopted in July 1923 - just months after Telefunken there had taken a 400 -kW machines transmitter in operation - the service on. She was fed with 25 kV and sent to 49.2 kHz ( 6100 m). At least one other Poulsen transmitter ( another source: three) stood in Malabar.

Transmit antennas Malabar

Interestingly transmitter systems in Malabar is also the construction of a slope antenna, which was built above the valley behind the station buildings. The antenna is held by transverse tension, which are performed from peak to peak across the valley, at the height. The highest part of the antenna is about 480 m above the valley floor and about 800 m higher than the antenna feed. The actual antenna consists of seven copper wires of 35 mm ² cross-section. It is 2000 m long, 240 m wide and oriented 324 ° exactly Kootwijk in the Netherlands.

Importance

Developed by Valdemar Poulsen arc technique coined - together with the machine stations - nearly ten years the intercontinental radio communications in point-to - point operation with large transmission power on the long wave. What distinguished the arc transmitter from the transmitter equipment, the possibility was also operate mobile systems with small power economically. Applications found in many fleets in the world.

From the mid- 1920s caused by the vacuum tube technology and the new medium of shortwave reliable and manageable opportunities for wide area radio: They prepared the long-wave colossi an end.

Literature sources

• Heinrich Busch: The Time of the arc transmitter. 2006 ( Online).
• Nauticus. Shipping, shipbuilding, marine, marine research. 1938, ISSN 0077-6203.
• Telefunken -Zeitung. No 40/ 41, October 1925, ZDB - ID 961314-6.
• Fritz Trenkle: The German radio message attachments to 1945 Army, Navy, aviation.. Volume 1: The first 40 years Hüthig, Heidelberg, 1989, ISBN 3-7785-1952-2.
• Dieter Vierus: CQD, SOS, MAYDAY. From the pop radio transmitter for satellite radio. 100 years of history of the marine radio. DSV -Verlag, Hamburg 1999, ISBN 3-88412-300-9.
• Jonathan Zenneck: Textbook of wireless telegraphy. 2 completely reworked and enlarged edition of the Guide. Enke, Stuttgart 1913.