Field strength
(13) Field strength. The electric field strength in the horizontal plane. (14) Free space field strength. The field strength that would exist at a point in the absence of waves reflected from the earth or other reflecting objects. (15) Frequency departure. The amount of variation of a carrier frequency or center frequency from its assigned value. (16) Frequency deviation. The peak difference between modulated wave and the carrier frequency. (17) Frequency modulation. A system of modulation where the instantaneous radio frequency varies in proportion to the instantaneous amplitude of the modulating signal (amplitude of modulating signal to be measured after pre-emphasis, if used) and the instantaneous radio frequency is independent of the frequency of the modulating signal. (18) Frequency swing. The peak difference between the maximum and the minimum values of the instantaneous frequency of the carrier wave during modulation. (19) Multiplex transmission. The term multiplex transmission means the simultaneous transmission of two or more signals within a single channel. Multiplex transmission as applied to FM broadcast stations means the transmission of facsimile or other signals in addition to the regular broadcast signals. (20) Percentage modulation. The ratio of the actual frequency deviation to the frequency deviation defined as 100% modulation, expressed in percentage. For FM broadcast stations, a frequency deviation of 75kHz is defined as 100% modulation.