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would be equivalent to a desired operational coverage and the relation must be assessed regionally.
6.2.3.8 Some States have recorded data on NDBs and their effective coverage; and collection of similar information
would be a practical way of obtaining an assessment of effective coverage in terms of rated coverage of facilities in a given
area. This information would also be useful for future regional planning. In order to reduce the number of factors involved in
assessing effective coverage, it would be desirable to establish criteria for determining the limit of useful coverage in terms of
the reaction of the bearing indicator. The data referred to previously, together with measurements of actual field strength
within the coverage of the NDB, would also permit determination of the effectiveness of existing installations and provide a
guide to improvements that may be necessary to achieve a desired effective coverage.
ATT C-61 23/11/06
Annex 10 — Aeronautical Communications Volume I
6.3 Coverage of NDBs
6.3.1 Introduction
6.3.1.1 The following studies have been based on the latest propagation and noise data available to the ITU. They are
included in this Attachment as general guidance in respect of NDB planning. Attention is called particularly to the
assumptions made.
6.3.1.2 When applying the material, the validity of the assumptions in respect of the particular conditions under
consideration should be carefully examined and, in particular, it should be noted that the assumed signal-to-noise ratios
require considerable further study before they can be accepted as representative of the ratios limiting useful reception.
6.3.2 Assumptions
1. Operating frequency — 300 kHz.
Reference is made, however, where appropriate, to frequencies of 200 kHz and 400 kHz.
2. a) Average soil conductivity:
(σ = 10–13 e.m.u.)
b) Average seawater conductivity:
(σ = 4.10–11 e.m.u.)
3. The level of atmospheric noise (RMS) which is likely to prevail: 1) by day, 2) by night, over land masses, within the
belts of latitude mentioned. [The values of expected noise have been derived from Recommendation ITU-R P.372-6 and have
been taken as the average noise by day and by night during equinox periods, i.e. the values which are likely to be exceeded
20–25 per cent of the year.]
4. Input powers to the antenna of the NDB of:
a) 5 kW
b) 1 kW
c) 500 W
d) 100 W
e) 50 W
f) 10 W
5. The following average values of radiation efficiencies of antennas, i.e. the ratio of:
Radiated power
Input power to antenna
Input power Radiation efficiency
to antenna of antenna
a) 5 kW 20% (–7 dB)
b) 5 kW 10% (–10 dB)
c) 1 kW 8% (–11 dB)
d) 500 W 5% (–13 dB)
e) 100 W 3% (–15 dB)
f) 50 W 2% (–17 dB)
g) 10 W 1% (–20 dB)
h) 10 W 0.3% (–25 dB)
23/11/06 ATT C-62
Attachment C Annex 10 — Aeronautical Communications
i) The figure for a) is included because it is possible to realize this efficiency by the use of a more elaborate antenna
system than is usually employed.
ii) The figure for h) is included because many low power NDBs use very inefficient antennas.
6. An admittance band of the ADF receiver of 6 kHz.
7. Required ratios of signal-(median) to-noise (RMS) of:
a) 15 dB by day;
b) 15 dB by night.
6.3.3 Results of studies
A.— Minimum field strengths required at the boundary of the rated coverage:
By day for By night for
Latitude 15 dB S/N ratio 15 dB S/N ratio
5°N – 5°S 320 μV/m (+50 dB) 900 μV/m (+59 dB)
5° – 15°N&S 385 μV/m (+39 dB) 700 μV/m (+57 dB)
15° – 25°N&S 340 μV/m (+32 dB) 320 μV/m (+50 dB)
25° – 35°N&S 18μV/m (+25 dB) 120 μV/m (+42 dB)
>35°N&S 18μV/m (+25 dB) 150 μV/m (+35 dB)
A star shown against a figure indicates that a higher value of field strength — probably 2 or 3 times the values shown
(plus 6 to plus 10 dB) — may be necessary in the presence of high aircraft noise and/or industrial noise.
B.— Coverage of NDBs (expressed in terms of the radius of a circle, in kilometres,
with the NDB at the centre) which may be expected under the assumptions made:
1) By day, 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 320 300 170 120
5° – 15°N&S 510 470 320 250
15° – 25°N&S >600 600 450 350
25° – 35°N&S >600 >600 600 500
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