1、 Rec. ITU-R P.368-9 1 RECOMMENDATION ITU-R P.368-9 Ground-wave propagation curves for frequencies between 10 kHz and 30 MHz (1951-1959-1963-1970-1974-1978-1982-1986-1990-1992-2005-2007) Scope This Recommendation provides information on the field strength and its dependence on ground characteristics
2、due to ground-wave propagation at frequencies less than 30 MHz. The ITU Radiocommunication Assembly, considering that, in view of the complexity of the calculation, it is useful to have a set of ground-wave curves for a range of standard frequency values and ground characteristics, recommends 1 that
3、 the curves of Annex 1, applied in the conditions specified below, should be used for the determination of ground-wave field strength at frequencies between 10 kHz and 30 MHz; 2 that, as a general rule, these curves should be used to determine field strength only when it is known that ionospheric re
4、flections will be negligible in amplitude; 3 that these curves should not be used in those applications for which the receiving antenna is located well above the surface of the Earth; NOTE 1 That is, when rd1the field-strength curve obtained by the Millington method ( 1) lies between the curves corr
5、esponding to the two different electrical properties E(1, 1) and E(2, 2). At the distance d = 2 d1, where d1is the distance from the transmitter to the border separating the two sections, the curve goes through the mid-point between the curves E(1, 1) and E(2, 2) provided that the field strength is
6、labelled linearly in decibels. In addition, the same curve approaches an asymptote, which differs by m dB from the curve E(2, 2) as indicated in Fig. 12, where m is half the difference in decibels between the two curves E(1, 1) and E(2, 2) at d = d1. The point at d = 2 d1and the asymptote make it ea
7、sy to draw the resulting field-strength curve. Figure 13 shows the curve for a two-section path with electrical constants changing from 2, 2to 1, 1where the modulus of the complex permittivity | (1, 1) | | (2, 2) |. The above-mentioned procedure can be applied here bearing in mind that the asymptote
8、 is now parallel to the curve of the E(1, 1). 16 Rec. ITU-R P.368-9 For paths consisting of more than two sections, each change can be considered separately in the same way as the first change. The resulting curve has to be a continuous curve, and the portions of curves are displaced parallel to the
9、 extrapolated curve at the end of the previous section. The accuracy of the graphical method is dependent on the difference in slope of the field-strength curves, and is therefore to an extent dependent on the frequency. For the LF band, the difference between the method described in 1 and this appr
10、oximate method is normally negligible, but for the highest part of the MF band the differences in most cases will not exceed 3 dB. Figures 14 to 50 contain field-strength curves as a function of distance with the electrical characteristics of the ground as a parameter. Rec. ITU-R P.368-9 17 18 Rec. ITU-R P.368-9 Rec. ITU-R P.368-9 19 20 Rec. ITU-R P.368-9 Rec. ITU-R P.368-9 21 22 Rec. ITU-R P.368-9 Rec. ITU-R P.368-9 23 24 Rec. ITU-R P.368-9 Rec. ITU-R P.368-9 25 26 Rec. ITU-R P.368-9 Rec. ITU-R P.368-9 27 28 Rec. ITU-R P.368-9 Rec. ITU-R P.368-9 29 30 Rec. ITU-R P.368-9
