: Formulas for calculating the interference noise power in base band and interference reduction factor of frequency modulated TV system interfered by RF signals are derived. The RF signal may be a FM telephone signal

a FM television signal or an impulse radar signal. Some useful conclusions based on theoretical analysis are also presented. The approximation used in calculating the interference reduction factor is discussed

and then some typical interference objectives including RF protection ratio and base band signal-to-noise ratio are calculated in detail.In the formulas derived

almost all important variables which affect the value of the interference reduction factor have been taken into account. These variables are carrier frequency off-set value

pre-emphasis factor

weighting factor

video spectral distribution and nominal peak to peak frequency deviation. If neglecting all the variables except nominal peak to peak frequency deviation

the derived formula may be reduced very closely to the approximate expression of results from objective measurements given by CGIR Rep. 634-1. This shows that the formulas given in this paper are a theoretical development to that local experimental knowledge. It is now possible to compute the interference into FM TV systems and the computation is as reliable as that in telephony. It is believed that the derived formulas will be usefulto interference analysis and co-ordination.