Milestones:Yosami Radio Transmitting Station, 1929

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 [3]. 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].

(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 [1]. 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.
(4) 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 [4]. 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[5].
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.