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>35°N&S >600 >600 >600 500
Input power to antenna
(e) (f) (g) (h)
Latitude 100 W 50 W 10 W 10 W
5°N – 5°S 50 30 10 <10
5° – 15°N&S 150 90 40 10
15° – 25°N&S 220 160 70 45
25° – 35°N&S 330 250 130 80
>35°N&S 330 250 130 100
ATT C-63 23/11/06
Annex 10 — Aeronautical Communications Volume I
2) By night, over land, and for 15 dB S/N ratio at the boundary of the coverage:
Input power to antenna
(a) (b) (c) (d)
Latitude 5 kW 5 kW 1 kW 500 W
5°N – 5°S 190 150 185 150
5° – 15°N&S 210 180 110 170
15° – 25°N&S 320 300 170 120
25° – 35°N&S 390 390 280 200
>35°N&S 390 390 390 310
Input power to antenna
(e) (f) (g) (h)
Latitude 100 W 50 W 10 W 10 W
5°N – 5°S 120 <10 <10 <10
5° – 15°N&S 125 115 <10 <10
15° – 25°N&S 150 130 <10 <10
25° – 35°N&S 100 170 <25 <15
>35°N&S 180 120 <50 <30
6.3.3.1 In all of the above tables, it has to be noted that:
a) the distances are given in kilometres, in accordance with ITU practice;
b) the figures in the final columns, with the heading 10 W, are calculated on the assumption that the low power NDB
uses a very inefficient antenna (see 6.3.2, assumption 5 h));
c) a star shown against a figure indicates that the coverage may be limited by aircraft and industrial noises.
6.3.3.2 It has also to be noted that:
a) if a frequency of 200 kHz were used in place of 300 kHz, this would not appreciably affect the coverage of low
power short range NDBs, but the coverage of the higher power, longer range beacons (for example, those with a
range of 150 km or more) would be increased, as compared with those shown in the tables, by about 20 per cent;
b) if a frequency of 400 kHz were used in place of 300 kHz this would not appreciably affect the coverage of low
power short range NDBs, but the coverage of the higher power, longer range beacons (for example, those with a
range of 150 km or more) would be decreased, as compared with those shown in the tables, by about 25 per cent;
c) use of an ADF receiver with a narrower band would, other things being equal, provide wider coverage for the same
radiated power of the NDB or, for the same coverage, an improved effective signal-to-noise ratio.
For example, if an admittance band of 1 kHz instead of 6 kHz were used, the coverage might be increased by as much as
30 per cent for the same radiated power or, alternatively, the effective signal-to-noise ratio might be increased by as much as
8 dB;
d) if a sector of the coverage of an NDB is over seawater, a greater coverage may be expected within that sector due to:
1) better ground wave propagation over seawater than over land;
23/11/06 ATT C-64
Attachment C Annex 10 — Aeronautical Communications
2) the noise level, which is highest over land, often drops fairly steeply with increasing distance from the land. It
might be assumed, therefore, that the distances shown in the tables could be increased by about 30 per cent by
day, and by about 20 per cent by night, when the path is over seawater;
e) if, however, the beacon is sited on an island remote from land masses (for example, in mid-Pacific or mid-Atlantic,
but not in the Caribbean), the coverage of the beacon is likely to be much greater, particularly in tropical latitudes,
than is indicated in the tables; and in such cases figures for coverage similar to those shown for latitudes more than
35°N and S may be assumed for all latitudes, due to the much lower level of atmospheric noise which prevails in
mid-ocean as compared with that experienced over, or in proximity to, land masses.
6.3.4 Limitation of coverage of a beacon at night due to “night effect”.
a) The distances, at night, at which the ground wave and sky wave components of the received field are likely to be
equal are as follows:
Frequency Over land Over sea
200 kHz 500 km 550 km
300 kHz 390 km 520 km
400 kHz 310 km 500 km
b) The distances, at night, at which the ground wave component of the received field is likely to exceed the sky wave
component by 10 dB are as follows:
Frequency Over land Over sea
200 kHz 300 km 320 km
300 kHz 230 km 300 km
400 kHz 200 km 280 km
c) It is, therefore, unlikely that reliable bearings can be obtained, at night, due to interaction of the two components of
the received field, at much greater distances than those shown in 6.3.4 b). These distances are independent of the
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