Arc transmitter
The arc transmitter , also called Poulsen transmitter after its inventor Valdemar Poulsen , was used to transmit messages in the long wave range and uses the negative differential resistance of an arc to generate vibrations.
Arc transmitters were used in the early 20th century through the late 1920s.
development
At the time of the first development of arc transmitters, the spark transmitters of the Marconi Company already existed in the form of pop-spark transmitters and machine transmitters . Disadvantages of this technique were:
- the machine transmitters only reached low frequencies, the spark transmitters had a low level of efficiency
- The spark transmitters caused strong interference - they were broadband, "dirty" transmitters. They produced a wide frequency spectrum, which prevents precise selection at the receiver; neighboring stations interfered with each other.
- Because of the long pauses between the individual attenuated wave trains of the spark transmitters, it was not possible to modulate them with speech or music - only Morse code could be used to transmit messages .
Nikola Tesla and the Canadian engineer Reginald Fessenden were the first to try to generate undamped waves with carbon electrodes, which they used in place of the spark gap in DC-excited spark transmitters. However, neither the frequency nor the energy of the generated vibrations were high enough for wireless telegraphy and telephony. Even the Englishman William Duddell was unable to meet the requirements for wireless telegraphy in 1900 with his "singing arc", which uses the electric arc method with carbon electrodes. It fed the arc via choke coils with direct current and connected a resonance circuit consisting of a coil and capacitor.
It was not until 1902 that Valdemar Poulsen succeeded in using an arc transmitter to generate undamped HF oscillations of sufficient frequency and energy using the basic circuit developed by William Duddell . He used a copper anode and a carbon cathode. The cathode rotated slowly and was automatically adjusted to a distance of 3–5 mm in order to achieve even burnout. For the transmitter to work properly, good cooling and deionization of the space between the electrodes were necessary. For this purpose, the copper anode and the “flame chamber” were cooled with water and a very strong magnetic field running across the flame “blew” the ions out of the arc. In addition, the arc burned in a hydrogen atmosphere . With this system undamped waves with frequencies up to 250 kHz (1200 m) were achieved. In 1904 Poulsen patented his system of the arc oscillator for undamped waves, the "Poulsen lamp", in 15 countries.
construction
The upper part with the strong cooling fins contains the combustion chamber with the two horizontally arranged electrodes. These are brought together briefly by the lever visible on the right to ignite the burning process. The two large coils supply the horizontal magnetic field. The motor visible under the lever turns the carbon cathode. The hydrogen-containing atmosphere was initially achieved by passing hydrogen through the combustion chamber. From 1906 on, a type of wick oiler was installed above the combustion chamber, which with a 1 kW transmitter put one to two drops of alcohol per second into the chamber and allowed it to evaporate.
advantages
Compared to the dampened vibrations of the pop-spark transmitters, the arc transmitter emits a much narrower frequency band and only a few spurious and harmonics . In this way, considerably larger ranges were achieved with the same transmission power and up to five times as many transmitters could be accommodated in one frequency band. On the other hand, the narrow-band transmission on the receiving end was no longer so easy to coordinate and only audible at a very specific point. Precise frequency agreements were now required for radio communication between two stations.
Technical adaptation
In order to use the new type of transmitter for wireless telegraphy, a few difficulties still had to be overcome. Unattenuated transmitters keyed in soundless telegraphy (A1) were not audible with the usual detector receivers, only a crack at the beginning of the Morse code indicated a transmitter. Poulsen and his colleague P. O. Pedersen developed a new type of detector: A battery- or spring-operated buzzer produced an audible tone to the rhythm of the received high frequency, such circuits were called "tikker" or "grinder".
The problem described here, which naturally also occurred with the machine transmitters and later with the tube transmitters , led to superimposition reception, which Reginald Fessenden ( Canada ) and 1905 Robert Goldschmidt ( Belgium ) had already considered in 1902 , but with the available (often mechanical ) Funding was not yet reliably feasible. It was not until 1913 that Alexander Meißner ( Telefunken ) succeeded in achieving the first flawless feedback reception using a circuit with a Lieben tube (based on Robert von Lieben ).
Another problem was the keying of the Poulsen transmitter. Since it takes a few seconds after each start until it oscillates stably, it cannot be keyed in its primary circuit. The solution was to use Morse code to change the resonant circuit coil and thus the transmission frequency by 1 to 5% ( FSK operation). In the receiver you could hear the second (keyed) frequency with the message; The first frequency with the "negative" Morse code was not used to transmit messages at that time. The modulation of the Poulsen transmitter with speech or music also caused difficulties. The microphone had to be connected in series with the antenna; at high transmission power, water-cooled multiple microphones were used to avoid overload. This made it impossible to talk to the transmitter remotely using a remote microphone.
It was not until 1913 that this problem could be satisfactorily solved by using a telephony throttle (named after its inventor Leo Pungs - from Lorenz Company - also known as the " Pungs throttle ") between the transmitter and the earth. This new component (it works according to the transducer principle) managed the modulation and keying of the high-frequency current with the help of three windings on a three-legged iron core with only 1% of the antenna power.
First transmitter
In 1904 Poulsen established a connection between Lyngby and Copenhagen (15 kilometers) and two years later over 270 kilometers between Lyngby and Esbjerg . In order to test all possibilities, international connections were necessary. Negotiations and a. with Telefunken failed. Poulsen therefore founded the "Amalgamated Radio Telegraph Company Ltd." with English investors, based in London . In 1906 there were radio links over 900 km between Denmark and Cullercoats and over 1500 km between Denmark and Knockroe in Ireland. The Knockroe station was intended for further experiments in the promising radio operation with arc transmitters across the Atlantic. But nothing came of it, in 1907 the English donors went bankrupt. The "Amalgamated" was dissolved without having concluded a single deal.
As a result, Poulsen sold the rights to his invention in 1908. In Germany, the C. Lorenz company acquired the patents and was able to sell telegraphy stations with outputs between 1.5 and 4 kW for fixed transmission systems to the Army over the next few years. The navy also showed interest and purchased from Lorenz Poulsen transmitters with outputs of up to 6 kW for use on large ships. From 1910 these systems were gradually equipped with telephony accessories. At German coastal radio stations, a 4 kW arc transmitter for telegraphy was only installed in Norddeich in 1911 ; telephony attempts were also made from 1912 onwards. Arc transmitters were not used on German merchant or passenger ships, at least there are no reliable reports about them. In 1914 Lorenz set up large stations with Poulsen transmitters in Königsberg and Posen .
The arc transmitter was very well received in the USA . Already during the world exhibition in 1904 in St. Louis Poulsen had advertised his invention and looked for investors. In 1909 Cyril F. Elwell acquired the Poulsen rights for the United States in Copenhagen and also bought a transmitter (100 watts) from Poulsen. By 1912 Elwell had built 14 transmission systems that connected the major cities on the west coast of the USA and further east into the country (including San Francisco, Portland, Seattle, Salt Lake City). At dumping prices, it successfully competed with traditional wired intelligence services.
The US Navy also showed interest and initially ordered a 100 kW transmitter. Elwell brought the engineer Leonard Fuller on board to realize this project . With its ability, the construction of transmitters with several hundred kilowatts of primary power consumption succeeded. The Navy built a worldwide radio network with Poulsen transmitters during the First World War . Larger naval bases such as B. San Francisco and Hawaii received the meanwhile proven technology with an output of several hundred kilowatts. All larger ships in the Navy were equipped with Poulsen transmitters of low to medium power.
Arc transmitters with primary powers of 100 kW and well above have been installed around the world. B. in England ( Portsmouth ), Greece ( Saloniki ) and Egypt ( Cairo ). In France, Elwell built large stations on the Eiffel Tower in 1915/16 , in Nantes and Lyon . The French Navy had been working with arc transmitters since 1908 (range 120 to 160 km). A transmission system operated with a Poulsen lamp was built near Bordeaux , the HF output was 1000 kW. One of seven transmission frequencies between 12.8 kHz and 21.7 kHz could be switched optionally. The transmitter weighed 80 tons, most of it was in the electromagnet. The antenna - suspended from 8 masts at a height of 250 m - covered a well-grounded area of 1200 m × 400 m.
Malabar radio station
The Dutchman Cornelis Johannes de Groot built what is probably the most powerful arc transmitter based on the Valdemar Poulsen system in Malabar ( Java / present-day Indonesia) in 1922/23 . The arc transmitter technology was chosen because all the components required for it could be manufactured in the country itself. With a primary power consumption of 2400 kW, the transmitter was connected to the major Dutch station in Kootwijk (point-to-point traffic) over a distance of 11,500 km .
The station with the call sign PKX started service in July 1923 - just a few months after Telefunken had put a 400 kW machine transmitter there into operation. It was fed with 25 kV and transmitted on 49.2 kHz (6100 m). At least one other Poulsen transmitter (other source: three) was in Malabar.
Malabar transmitting antennas
Another interesting feature of the transmitter in Malabar is the construction of a slope antenna that was erected above the valley behind the station buildings. The antenna is held at the same height by transverse tensions that run from peak to peak across the valley. 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 strands, each 35 mm² in cross-section. It is 2000 m long, 240 m wide and precisely aligned with Kootwijk in the Netherlands at 324 °.
meaning
The arc technology developed by Valdemar Poulsen - together with the machine transmitters - shaped intercontinental radio communications in point-to-point operation with high transmission power on long wave for almost ten years. What distinguished the arc transmitter from the machine transmitter was the ability to operate mobile systems with low power economically. They were used in many fleets around the world.
From the mid-1920s, tube technology and the new medium of shortwave resulted in more reliable and more manageable options for long-distance radio traffic: They put an end to the long-wave giants for overseas radio. However, longitudinal waves are still used to transmit messages to submerged submarines, for which some of the former large stations are still used.
literature
- Heinrich Busch: The time of the arc transmitter . 2006 ( seefunknetz.de ).
- Nauticus. Shipping, shipbuilding, marine, marine research . 1938, ISSN 0077-6203 .
- Telefunken newspaper . No. 40/41 , October 1925, ZDB -ID 961314-6 .
- Fritz Trenkle : The German radio communication systems until 1945. Army, navy, aviation . tape 1 : The first 40 years . Hüthig, Heidelberg 1989, ISBN 3-7785-1952-2 .
- Dieter Vierus: CQD, SOS, MAYDAY. From pop-spark transmitters to satellite radio. 100 years of marine radio history . DSV-Verlag, Hamburg 1999, ISBN 3-88412-300-9 .
- Jonathan Zenneck : Textbook of Wireless Telegraphy . 2. Completely revised and increased edition of the guide. Enke, Stuttgart 1913.
