47 C.F.R. § 73.190 Engineering charts and related formulas.
Title 47 - Telecommunication
(a) This section consists of the following Figures: 2, r3, 5, 6a, 7, 8, 9, 10, 11, 12, and 13. Additionally, formulas that are directly related to graphs are included. (b) Formula 1 is used for calculation of 50% skywave field strength values.
The skywave field strength, F The slant distance, D, is given by: The geomagnetic latitude of the midpoint of the path, Φ Φ The short great-circle path distance, d, is given by: Where: d° = arccos[sin a Where: a a b b a b Note (1): If |F Note (2): North and east are considered positive; south and west negative. Note (3): In equation (7), k = −1 for west to east paths (i.e., b (c) Formula 2 is used for calculation of 10% skywave field strength values.
The skywave field strength, F F Where: Δ = 6 when | FM| < 40 Δ = 0.2 | FM| − 2 when 40 ≤ | F Δ = 10 when | F (d) Figure 6a depicts angles of departure versus transmission range. These angles may also be computed using the following formulas:
Where: d=distance in kilometers n=1 for 50% field strength values n=2 or 3 for 10% field strength values and where K1=0.00752 K2=0.00938 K3=0.00565 Note: Computations using these formulas should not be carried beyond 0.1 degree. (e) In the event of disagreement between computed values using the formulas shown above and values obtained directly from the figures, the computed values will control. [28 FR 13574, Dec. 14, 1963, as amended at 30 FR 12720, Oct. 6, 1965; 33 FR 15420, Oct 17, 1968; 48 FR 42959, Sept. 20, 1983; 49 FR 43963, Nov. 1, 1984; 50 FR 18844, May 2, 1985; 51 FR 4753, Feb. 7, 1986; 52 FR 36879, Oct. 1, 1987; 56 FR 64869, Dec. 12, 1991]
Title 47: Telecommunication
PART 73—RADIO BROADCAST SERVICES
Subpart A—AM Broadcast Stations
§ 73.190 Engineering charts and related formulas.