Understanding television's grade A and grade B service contours

The Grade A and Grade B service contours of a television broadcast station are used for a host of administrative purposes by the FCC including the regulation of CATV systems. Additionally, the contours are used by most stations for promotional and marketing purposes. The numerical values associated with these contours represent levels of field strength; consequently, assumptions were made in their determination as to noise limitation, the antenna gain, and transmission-line loss of the receiving system. Also, consideration was given to the subjective nature of the picture quality and the statistical variation of the field strength with time and location. The nature of these variables is discussed and the assumed values are tabulated in a format suitable for easy understanding and for analysis of possible future changes.