Notes on Radio Transmission

Considerable data on radio transmission have been obtained the past few years in connection with the establishment and operation of various radio-telephone services by the Bell System. It is the purpose of these notes to present certain aspects of some of these data which may be of interest in the development of a general physical picture of radio transmission and in indicating the effects of disturbances accompanying storms in the earth's magnetic field. The general results which are arrived at are: 1. Neglecting short time fading, the maximum field strength received at a given point for frequencies up to at least 4 megacycles are in general agreement with those calculated by the inverse-distance law and the minimum field strength (over-water transmission) are in approximate agreement with those calculated by the Austin-Cohen formula. 2. There appears to be a daylight absorption band in the neighborhood of 40 kilocycles (North Atlantic transmission) which reduces minimum daytime fields in that vicinity below the minimum limit given above. 3. The effect of solar disturbances is to increase the absorption to "sky wave" transmission throughout the entire radio-frequency spectrum generally and to reduce or eliminate the 40-kilocycle absorption band thereby increasing daylight fields for transmission on frequencies in that vicinity.