Interference between Very-High-Frequency Radio Communication Circuits

Interference between different radio circuits is an old problem, one which in the past generally has been solved by trial and error and by hand tailoring (special filters, etc.). With the general increase in the usage of radio communication, however, the amount of potential interference is greatly increased. This paper will be concerned principally with the v.h.f. problem. There is generally a large difference between transmitting and receiving power levels. As a result, spurious radiations, spurious responses, and lack of sufficient receiver selectivity may in many instances cause interference. Situations are described in which such interferences are likely. In mobile systems interference can occur if the interfering station is close enough to "capture" it from the desired signal. This, in turn, depends upon the selectivity and spurious response of the receiver and the amount of spurious radiation from the transmitter. The problem can be approached in a statistical manner. The types of spurious radio behavior which are common causes of interference are discussed. Sample measurements are given to illustrate the relative magnitude of the various modes of behavior. Formulas are given which permit computation of the frequency of the disturbances. A method is described for making charts suitable for a given type of equipment from which the spurious frequencies can be read directly as a function of the operating frequency.