Abstract
Communicati u test on short waves across the Pacific was carried out in order to see what wave length should be used for Trans-Pacific communication and to find the wave length which gives the signal strength at a certain distance both at night and in the daytime.
The 500 watts short wave transmitter was installed on board S. S. Shinyo Maru for that purpose, while the short wave transmitters of the Training School of the Departmcnt of Communicatons, Shiba, Tokyo, of Iwatsuki Radio Station near Omiya and of Ottishi Radio Station near Nemuro were utilized for the transmission to S. S. Shinyo Maru.
The wave lengths of these stations were as follows;
Transmission was done two or three times a day by each station, so that we should be able to compare the daytime and night transmissions.
S. S. Shinyo Maru left Yokohama on Feb. 21 and arrived at San-Francisco via Honolulu on March 8th this year.During her voyage the stations concerned sent test signals as scheduled which were received by others every day. During her homeward voyage from the departure at San Francisco on March 17th to the arrival at Yokohama on April 2nd, We made the same test.
The signal strength measured every day were plotted against distances, from which we find the following facts;
(1) 40.5 meter wave may be used with fairly good result for the whole range up to 8400 kilometers at night.
(2) 21.5 meter wave is far better than 40.5 meter wave for daytime transmission.
3) Skip distance phenomena is remarkably shown by the audibility curves, and (i) The shorter the wave the more skip distance we have. (ii) The shorter wave skips more at night than in the daytime.
(4) For a certain distance there is one wave which gives the same signal strength both at night and in the daytime. From the curves we got 21.5 meter for 3100km., 30 meter for 1500km. and40.5 meter for 520km. A curve is drawn from these data showing a relation between the distance and the wave length, which is very valuable for choosing the wave length to be used for a certain distance. It must be noted that this curve is good only in this season(February 20 to April 2)of the year. Probably the curve will be lowered in summer and raised in winter, becau e the shorter wave is suitable in summer and the longer wave in winter, which fact was evidenced by our short wave test of more than one year.
