Transmission Loss in Radio Propagation

The utility of the concept of transmissionloss in radio-propagation analysis is explored. The transmission loss of a radio system is defined to be the ratio of the power radiated from the transmitting antenna to the resulting signal power available from a loss-free receiving antenna. After discussing some methods of measuring transmission loss, its calculation for representative systems is discussed. It is shown that a measure of transmission loss often adopted, namely the attenuation relative to the free-space value, sometimes leads to errors and confusion in the presentation of the results of measurements and in applications to radio systems; the use of the over-all transmission loss of a system avoids these pitfalls. A discussion is given of the expected variation with time (fading) of the transmission loss expected for radio systems involving ionospheric or tropospheric propagation. This discussion involves the theory of the Rayleigh distribution and its limitations in such applications. A definition is then derived for the effective noise figure of a radio system which includes the external noise picked up on the receiving antenna. This definition is used to explain the method of determining the maximum range of a radio system. Finally a discussion is given of the maximum range of a radio system as limited by interference from other radio signals plus noise rather than from noise alone.