Signal Contour

Signal contours are either modeled (estimated) or measured field strengths at a given level. Contours are given confidence levels, most commonly, F(50,50), which means that the predicted electromagnetic field strength occurs at 50% of the receivers 50% of the time. In land mobile radio, the F(50,50) value is employed in calculating the "service contour." The F(50,10), which means that the predicted electromagnetic field strength occurs at 50% of the receivers 10% of the time, value is used in the calculation of the "interference contour." 47 CFR 74.683(a) states the unit of measure of ech contour shall be in dB above one micro-volt per meter, which is written as dBµ, or often as dBu, with the "u" substituting for the Greek letter mu "µ."

Contours may also be mathematically altered to correct for differences in height or to over-simplify accounting for adjacent channel power ratio across dissimilar modulation techniques and adjacent channel separation rather than employ TIA TR8 TSB-88.1 methodology. The use of contour values in this manner is a rough guide, rather than an attempt at precise measurement and also consensus process which may change frequently, unless the methodology is codified into FCC Rules and Regulations (i.e., 90.187 on VHF and UHF trunking).

Television

Grade	Channels	Contour
A	2-6	68 dBµ F(50,50)
A	7-13	71 dBµ F(50,50)
A	14-69	74 dBµ F(50,50)
B	2-6	47 dBµ F(50,50)
B	7-13	56 dBµ F(50,50)
B	14-69	64 dBµ F(50,50)

FM Broadcast Radio

Service	Contour
Protected Service Area	95.563 dBµ F(50,50) (= 60 mV/m)

Land Mobile Radio

Band	Frequencies	Service Contour	Interference Contour
VHF Low Band	30-50 MHz	31 dBµ F(50,50)	13 dBµ F(50,10)
VHF High Band	150-174 MHz	37 dBµ F(50,50)	19 dBµ F(50,10)
UHF	450-512 MHz	39 dBµ F(50,50)	21 dBµ F(50,10)
	700 and 800	40 dBµ F(50,50)	22 dBµ F(50,10)

Related Links

• Handy FCC Conversion Utilities
• Technical Factors Affecting the Assignmant of Facilities in the Domestic Public Land Mobile Radio Service - Carey, 1964
• Development of VHF and UHF Propagation Curves for TV and FM Broadcasting - Damelin, Daniel, Fine, and Waldo, 1966
• 73.683 Field strength contours and presumptive determination of field strength at individual locations
• 90.187 Trunking in the bands between 150 and 512 MHz
• DA 02-1319 Analytical Method for Determining Additional Frequency Coordination Requirements for Certain Private Land Mobile 150-470 MHz Applications
• Adjacent Channel Power Ratio (ACPR) at Wikipedia
• Coverage Impact of Implementing Narrowband Equipment - Olson, 2010