Milestones:Yosami Radio Transmitting Station, 1929


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Kariya City, Japan
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Yosami Radio Transmitting Station, 1929

In April 1929, the Yosami Station established the first wireless communications between Japan and Europe with a long wave operating at 17.442 kHz. An inductor-type high-frequency alternator provided output power at 500 kW. The antenna system used eight towers, each 250m high. The facilities were used for communicating with submarines by the Imperial Japanese Navy from 1941 to 1945 and by the United States Navy from 1950 to 1993.

Establishment of wireless communications in Japan

Before the First World War, Japan did not have its own overseas communication networks and depended on the wired networks operated by a foreign company. After the First World War, the Japanese government recognized that its own communication network was indispensable for dealing with the increasing amount of trade and diplomatic negotiations and decided to establish the long wave wireless transmitting stations for communications between Japan and the US and between Japan and Europe. The station for communication with US was established in 1927 in Iwaki, north of Tokyo, and the station for Europe in 1929 in Yosami near Nagoya.

Long wave generation using machine-senders

In the 1920s when there was no vacuum tube with high output power, long waves (continuous carrier waves) with high output power were generated by machine-senders, i.e., high frequency (HF) generators. Two types of generator were proposed for the machine-senders, as described in the following item (h). In the Yosami station, an inductor-type alternator was selected with the idea of high output power. The station started communications to Warsaw in Poland on April 15, 1929 as the first destination with a long wave of 17.442kHz and output power of 500kW. Communications to Berlin, Paris and London followed in turn.[1] By using the generator with such high output power, the long wave could cross a long distance of 9000km, i.e., the Eurasian Continent. Long wave stations around the world in the 1920s are shown in Table 1.[2]

Long wave transmitting stations around the world in the 1920s.

Area Name of Station Wavelength (km) Output Power (kW) Country
North America Rocky Point, NY 16.12/16.45 200/200 USA
North America Coram Hill, NY 17.5 200 USA
North America New Brunswick [N.J.] 13.75/13.265 200/200 USA
North America Marion [Mass.] 11.62/13.505 200 USA
North America Tuckerton [N.J.] 15.9 200 USA
North America Barnegat [N.J.] 16.7 200 USA
North America Bolinas [Calif.] 13.345 200 USA
North America Kahuku [Hawai] 16.3/16.975 200/200 USA
South America Rio de Janeiro 19 400 Brazil
South America Monte Glande 12.65 500 Argentina
South America Buenos Aires 16.8 500 Argentina
Europe Nauen 13/18.06 400/400 Germany
Europe Eilvese 14.65 200 Germany
Europe Carnarvon 14.1 200 United Kingdom
Europe Rugby 5 150 United Kingdom
Europe St. Assise 19.675/14.3 400/400 France
Europe Lafayette 19.1 400 France
Europe Torrenuova 14.45 500 Italy
Europe Kootwiyk 17.85 500 Holland
Europe Verberg 17.4 200 Sweden
Europe Stavanger 12.14 100 Norway
Europe Warsaw 18.28 200 Poland
Europe Ruysselede 18.52 500 Belgium
Asia Marabar 15.6 500 Java
Asia Saigon 20.55  ?? Indochina
Asia Iwaki 14.6 500 Japan
Asia Yosami 17.2 500 Japan
Oceania Sydney  ??  ?? Australia
Africa Abu Zabal 11 500 Egypt
  • Grimeton long wave transmitting station in Verberg of Sweden was registered as a World Heritage site by UNESCO in 2005.[3]

Advancement of short wave technology

In those days, short wave communication technologies had rapidly advanced, because short waves reflect at the ionosphere and enables long-distance communications with smaller power than long waves transmitted as ground waves. Within several years after completion of the Yosami Station, therefore, its long wave facilities became auxiliary ones for periods when short waves could not be used because of fluctuations of the ionosphere in winter.[4] Due to the success of the short waves, the Iwaki long wave transmitting station for communications with the US was dismantled and many other long wave stations in the world were also replaced with the short wave stations.

Submarine communications using long waves

As soon as the Second World War began, long waves were highlighted again. Electromagnetic waves penetrate more deeply into water with lower frequency; the penetration depth is almost 10-20m in the region of long waves.[5] Due to this feature, the long wave facilities in the Yosami Station came to be used for submarine communications by the Japan Navy during the War. After the War, the US Navy reused the Station for submarine communications during 1955-1993.[6]

Yosami was opened as the first long wave wireless communications station between Japan and Europe in 1929 and operated for more than 60 years in spite of advancements in short wave technologies. In these periods, the Station served for trade and diplomatic negotiations between Japan and Europe before the Second World War and for the submarine communications during and after the War. Now, the main long wave facilities once used at the Station are preserved in the newly-built Yosami Memorial Museum next to the original site and open to the public. The IEEE Milestone plaque may be visited at the museum.

Technical Details of the Yosami Station

The outstanding feature of long wave facilities at Yosami Station is the generation system to obtain long waves with high output power. To achieve a long wave of 17.442kHz and high output power of 500kW, a system combining inductor-type alternator and frequency-multiplying transformer was used, in which the alternator generated a frequency of 5.814kHz and the transformer tripled it to the required frequency, i.e. 17.442kHz. In those days, there were two methods for producing long waves; one was the use of the Alexanderson-type HF generator which was invented by Ernst Alexanderson,[7][8] and the other the use of the system combining conventional inductor-type alternator and multiplier transformer.[5][9] Both types of generator had many inductors like cogwheels on the periphery of the rotor and generated high frequency currents induced by inductor revolution, although the structure of rotor in each generator was quite different. The Alexanderson-type generator had a very narrow and light rotor, which enabled higher rotating speed, i.e., high frequencies without any frequency multipliers, while the output power was low, typically about 200kW because of low magnetic flux. This generator is already designated as an IEEE Milestone in 1992 under the name of “ Alexanderson Radio Alternator, 1904”.[10] On the other hand, the conventional inductor-type alternator used at the Yosami Station had a wide and heavy rotor as described in Table 2,[11] which enabled higher output power, though the rotating speed was slower than that of the Alexanderson-type and, as a result, it was necessary to use the frequency multiplier. For the Yosami Station, the inductor-type generator was selected because the long wave had to cross over the uneven Eurasian Continent between Japan and Europe with a long distance of 9000 km, but not the flat ocean.

Comparison of the generators between Yosami and Grimeton Stations

Until quite recently, two stations, Yosami Station in Japan and Grimeton Station at Verberg in Sweden, have remained the long wave facilities. Both stations are in a striking contrast; the Yosami Station employed the conventional inductor-type generator made in Germany, while the Grimeton Station employed the Alexanderson-type generator made in the US. The Yosami Station was dismantled in 2006 and the whole system was preserved in the newly-built Yosami Memorial Museum next to the original Yosami Station site. The Grimeton Station, however, is still alive and was designated a World Heritage site by UNESCO in 2005.[3] The Yosami and Grimeton Station generators are compared in Table 2. According to some reports, Telefunken in Germany shipped the last and largest generator with output power of 550kW as a machine-sender to the Yosami Station in Japan in 1928.[5][12] From these reports, it is presumed that the alternator in Yosami Memorial Museum is the largest remaining inductor-type generator in the world.

Configuration of transmitter and revolution speed control

The second feature of the Yosami Station is the method for stabilizing the frequency of long waves. The Station has two sets of transmitters for current and backup uses. Each set was composed of 4 machines, i.e., induction motor (920kW), DC generator (860kW), DC motor (730kW) and inductor-type alternator (700kVA) connected in series. Here, it should be noted that the alternator was not directly driven by the induction motor but by DC machines in the line.[4] The rotating speed of the alternator was measured and transmitted to the DC generator through a feedback loop so that the DC generator changed the DC output power according to the rotating speed. This is the so-called Ward-Leonard feedback system to obtain the stable rotating speed of the alternator. As a result, the frequency of long waves was kept constant.

Signaling and antenna system

The last feature is the antenna system. Signaling was done by Morse signals obtained by making the carrier wave of 17.442kHz off and on intermittently in the signal circuit.[4] Then the Morse signals were sent to 16 antenna wires mounted on 8 towers 250m high and transmitted skyward. Antenna specifications were as follows; electrostatic capacity was 0.06μF, specific wave length was 8700m, and total resistance was 2.6Ω. The lower part of the towers weighing 300 tons was isolated from the ground by ceramic insulators. Under the whole area of antenna wires of 1760m by 880m, earth wires of copper were buried at a depth of 60cm.  The Yosami Station opened in 1929, in which the last and the largest machine-sender of the conventional inductor-type alternator was installed. The long wave station facilities operated without any serious accidents for about 60 years. This high reliability shows the most sophisticated electrical engineering of the day, and the facilities should become a memorial as an industrial heritage site of communication technology.

Comparison of generator between Yosami and Grimeton Stations

Name of Station Long Wave Generation System Specifications of HF Generator and Frequency Multiplier Size and Weight of Rotor
Yosami HF Generator, Conventional inductor-type, Frequency Tripler Conventional inductor-type, (Designed by TELEFUNKEN and manufactured by AEG in Germany), No. of inductor: 256, Revolution speed: 1360 rpm, Output frequency: 5.814 kHz, Output power: 500 kW, Saturating Transformer-type, Input frequency: 5.814 kHz, Output frequency: 17.442 kHz Diameter: 1.87 m, Width: 1.1 m, Weight: 21.2 tons
Grimeton HF Generator only Alexanderson-type, (Manufactured by General Electric in USA), No. of inductor: 488, Revolution speed: 2115 rpm, Output frequency: 17.202 kHz, Output power: 200 kW Diameter: 1.6 m, Width: 0.08 m, Weight: 1.5 tons (estimated)


  1. ”Report on the Yosami Radio Transmitting Station”, (ed. by the Chubu Society for the Industrial Heritage, 1999), p.22. (in Japanese)
  2. E.Feyerabent et al,”Handwörterbuch des Electrischen Fernmeldewesens”, (Verlag von Julius Springer, Berlin, 1929), pp.607-608. (in German)
  3. 3.0 3.1
  4. 4.0 4.1 4.2 K.Tanaka, H.Nakamura, Y.Sugiura and S.Ishida,”YOSAMI Radio Transmitting Station: The Birthplace for the First Wireless Communications Between Japan and Europe with Long Wave in 1929”, Transactions of International Conference TICCIH 2005, pp.94-101.
  5. 5.0 5.1 5.2 G.Klawitler, K.Herold and M.Oexner, “Langwellen- und Längstwellenfunk,” (Siebel Verlag, 2000), pp.19-20, pp.36-37 and pp.43-45. (in German)
  6. J.L.Howard (the Commander of the US Navy):Letter of thanks on the occation of the Yosami Station’s sixtieth anniversary in 1989.
  7. US Patent No.902195: Ernst F. W. Alexanderson,”Telephone-Relay”,application filed at Jan.25,1908 and patented at Oct. 27, 1908.
  8. W.A. Graham: “Description of the 200kW Alexanderson Alternator”, Radio Corporation of America Circular No. 405, 1924.
  9. Patentschrift No.208260: R.Goldschmidt, “Verfahren und Schaltungsanordnung zur Erzeugung von Hochfrequenzströmen, insbesondere fur die drahtlose Telegraphia”. Patentiert im Deutschen reiche vom 5. Sep.1907 ab. Ausgegeben Den 20. Marz 1909. (in German)
  11. “Investigation Report on High Frequency Generator for Long Wave Communications”, (ed. by Specialist Committee of High Frequency Generator in Yosami Station, IEICE Tokai Section, 2007), pp.24-25. (in Japanese)
  12. TELEFUNKEN-ZEITUNG, No. 44, p. 95(1926). (in German)

More information

A report on the dedication ceremony


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