This paper is chiefly the detailed descriptions of the experimental researches on telegraph and telephone communications through channels by radio relay, which have been recently carried out in the Electrotechnical Laboratory. It begins with the historical sketch of radio telephone investigations in the Laboratory, stating that two-way radiophone system, wire and wireless telephone connection system, and carrier wave telegraph and telephone systems over overhead telegraph and telephone lines and power transmission lines, which have been newly developed quite independently of the art of the Western Hemisphere, were all born from the investigations in connection with the application of triode, which had been originally stimulated by the imperfection of T. Y. K radiophone system invented in 1912. It is stated next that, applying the results of the above investigations, the field experiments of two-way radiophone connected to wire lines were performed, the distance being extended from 15km between Toba and Kamishima at Ise Bay to 110km between Awoinori and Hakodate at the northern part and, further, to 220km between Fukuoka and Fuzan at the southern part.
Owing to the last severe earthquake in Japan, the Fukuoka-Fuzan experiment unfortunately had to be suspended and ac_??_rding little data have been collected. But at the Awomori-Hakodate circuit, all experimental data had been gathered before the disaster occurred. The data in detail involved in the present paper are therefore of the circuit.
The first experiment between Awomori and Hakodate was carried out as early as in 1920. On account of the shortage in power source and the disturbance from the spark transmitters, which were in use at that time, at the same stations, the purpose of the test was not attained. The second experiment was executed in 1923. The power source has been enlarged, the transmitting and receiving stations separated from each other at the distances of two or three kilometers, and the exsisting spark sets replaced by new valve transmitters. These alternations and improvements have made the stations possible to establish the simultaneous working of two-way radiophone and duplex radio-telegraph.
The radiophone transmitters are of plate circuit modulation type and of about 200 watts in total plate input of power tubes, while the, receiving sets are of retroaction type tube detector and two-stage audio-frequency amplifier. With these sets, conversation is easily accomplished through land lines, 290km and 370km long, connected respectively at each end, and the experiment was furthered with land lines, 290km and 720km long. The radio telegraph transmitters are of audible frequency modulation and of about 300 watts in plate input, the plate current of which is directly modulated by a 500 cycle 2500 volt alternator, while the receiving sets are also of retroaction type. For transmitters, of either station an antenna 30 meters high for telegraph and an antenna 60 meters high for telephone are employed, which are suspended from different wooden poles, situated nearby, while, for receivers, two different antennas 40 meters high are suspended from a single wooden pole. The wave lengths used were carefully selected not to interfere with those used in public radio telegraph stations in the vicinity 300 meters and 400 meters for telegraph, and 700 meters and 850 meters for telephone are at last adopted. The radio telegraph and telephone systems are now put in practical operation with satisfaction.
As the result of the present tests, it is concluded that a radiophone transmitter requires antenna power about three times as strong as a ratio telegraph transmitter does, and that the former consumes total input power six times as large as the latter. It is also estimated that a radiophone transmitter with land lines connected at both ends needs total power supply forty-eight folds as big as a radio telegraph transmitter.

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