Transatlantic radio telephone transmission

This paper gives analyses of observations of long-wave transmission across the Atlantic over a period of about two years. The principal conclusions which the data seem to justify are as follows: 1. Solar radiation is shown to be the controlling factor in determining the diurnal and seasonal variations in signal field. Transmission from east to west and west to east exhibit similar characteristics. 2. Transmission in the region bordering on the division between the illuminated and the darkened hemispheres is characterized by increased attenuation. This manifests itself in the sunset and sunrise dips, the decrease in the persistence of high night-time values in summer and the decrease in daylight values during the winter. 3. Definite correlation has been found between abnormal radio transmission and disturbances in the earth's magnetic field. The effect is to decrease greatly the night-time field strength and to increase slightly the daylight values. 4. The limit of the high-night-time value of signal field strength for transatlantic distance is essentially that given by the Inverse Distance Law. The normal daylight field strengths obtained in these tests can be aproximated by a formula of the same form as those earlier proposed but with somewhat different constants. 5. The major source of long wave static, as received in both England and the United States, is indicated to be of tropical origin. 6. In general, the static noise is lower at the higher frequencies. At night the decrease with increase in frequency is exponential. In day-time the decrease with increase in frequency is linear in the range of 15 to 40 kilocycles. The difference between day and night static is, therefore, apparently due largely to daylight attenuation. 7. The effect of the static noise in interfering with signal transmission. as shown by the diurnal variations in the signal-to-noise ratio, is found to be generally similar on both sides of the Atlantic. 8. Experiments in both the United States and England with directional receiving antennas of the wave antenna type show an average improvement in the signal-to-static ratio of about 5 as compared with loop reception.