A Tentative Statistical Study of Domestic Radio Interference

In B.S. 800 ¿Permissible Limits of Radio Interference¿ a certain degree of control of interference at the source is specified and in this paper an estimate is attempted of the probable reduction in the interference due to domestic sources which might be expected if B.S. 800 were applied. To this end a calculation is first made of the distribution among listeners of the susceptibility to interference based upon available statistics of the effective heights of aerials and of the magnitude of the coupling between aerial terminals and source of interference. This enables a calculation to be made for any coupling of the probability of interference to a given broadcast field when the distribution of intensity among interfering sources is known. The nature of the distribution of interfering voltages within a given type of appliance is studied and different types are compared. The statistical basis of the method of limitation adopted in B.S. 800 is explained and its implications in practice are considered. From this estimates are made of the distributions of the intensity of interference among domestic sources before and after suppression. From the formulae previously established it is then possible to calculate the ratio of the probability of interference after the application of B.S. 800 to that before, which gives the reduction of interference to be expected and also a relative estimate of the degree of protection afforded to the listener. The result discloses that a not unfavourable situation is provided by the British Standard in question, and although directions for the further reduction of interference at the source are suggested it is shown that substantial further amelioration would involve reduction of the susceptibility to interference of some receiving installations. This would mean some degree of standardization of such installations, the advantages of which are demonstrated.