Some Experiences with Short-Wave Wireless Telegraphy

An analysis is given of the factors that may be expected to determine the transmission phenomena peculiar to any given short-wave channel. It is considered that the wavelength that will give the greatest probability of satisfactory communication is determined by (a) the great circle distance between sender and receiver, (b) the geographical positions of the stations, (c) the time of year, and (d) the time of day. It is pointed out why the latitudes of the stations will be a pertinent factor. It is shown how in China in 1927-28 it became desirable to be able to predict the effects of the various factors, and in particular to predict the "best wavelength." The development of the British military short-wave system in that country and the inauguration of a series of tests are described. The method employed in the tests is critically examined. A summary is given of the working experiences and the results of the tests over the various "links." The diurnal and seasonal variations of best wavelength are recorded, and it is shown that the seasonal variations coincide approximately with the equinoxes. The results of traffic-handling experience and tests are combined into a "range-best wavelength diagram" for the belt of latitude lying between 30 deg. and 40 deg. North, and the question as to how closely the diagram might apply to other parts of the world is discussed.