Modulation of the Poulsen arc.

From the book 'Radio Telephony', 1918 by Alfred N. Goldsmith.

Loop modulation


In 1903, Valdemar Poulsen raised the arc to the status of the practically operative generator of radio frequency energy in considerable quantity by the following changes:
placing the entire arc in an atmosphere of hydrogen or a hydrocarbon vapor,
using a carbon electrode for the negative side and a copper anode water-cooled for the positive side,
rotating the carbon electrode slowly by motor drive and
placing an intense deflecting magnetic field transverse to the arc.

One disadvantage of the arc was, that when using telegraphy one could not hear if the carrier was present because the detector gave only direct current to the telephones. Poulsen solved this problem by inserting a 'tikker' between the detector and the telephones. The tikker was a switch, switching many times per second and in this way converting the direct current to a tone. The arc was very suitable for telephony and was normally modulated by several specially designed carbon microphones inserted in the ground connection of the transmitter.

500 kW Poulsen arc.     Poulsen arc

Description of the Poulsen arc:

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Harmsworth's Wireless Encyclopedia (1924)
Grundriss der Funken-Telegraphie (1920)


Schematic of transmitter Poulsen telephony receiver and transmitter.
Fly-wheel Poulsen arc for radio telephony. Used with small antenna systems. 
L being large in comparsion with the antenna inductance.  
Schematic of receiver
Portable station Poulsen transmitter station
Berliner - Poulsen arc for transportable military stations. Made by Telephone Manufacturing Corporation in Vienna. Station used for communication between Esbjerg and Lyngby in Denmark (distance of 270 km) in 1907.
The height of the antenna was 60 m, wavelength 1200 m, the supply power was 900 W and antenna power 300 W.
Modulated with 6 microphones in series (seen in the middle of the picture)
100 W arc 3 kW arc
100 W arc made by C. Lorenz in Berlin. 3 kW Berliner-Poulsen arc made by Telephone Manufacturing Corporation in Vienna.
Poulsen arc Arc made by the Danish Poulsen company Det Kontinentale Syndikat.
Arc from Telephone Manufacturing Corporation in Vienna.
The power was 10 - 25 kW
Austrian made arc
Ship station Berliner - Poulsen arc ship station.
Being used for either telegraphy or telephony. The arc, which was normally rated at about 8 kW input, is shown at the left. For telephony, it was used at reduced power, inasmuch as the multiple microphone transmitter at the middle would be incapable of modulating the full output. About 3.5 A (and never over 4) was passed through the transmitters.
3 kW German made arc Berliner - Poulsen 3 kW arc.
60 kW arc 100 kW arc
Federal Telegraph Company 60 kW Poulsen arc, corresponding to 500 V and 120 A.
It was this arc which has carried a portion of the trans-Atlantic traffic from Tuckertown, New Jersey to Hannover, Germany, a distance of 6500 km.
The antenna current was 120 A.
Federal Telegraph Company 100 kW Poulsen arc used for communication between the United States Naval Radio Station at Darien, Panama Canal Zone and Washington, a distance of 3000 km.
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