the ratio, expressed in decibels, between two voltages occurring at the output terminals of a given channel A, viz due to the wanted signal intended for channel A, and U'index B due to the unwanted si, in a set of radio channels arranged in the ascending order of their centre frequencies, the difference in frequency between the centre frequencies of two adjacent channels (IEC 50-713), kahe naaberkanali kesksageduste erinevus