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6.2.1.3 The application of rated coverage to frequency planning is governed by the following criteria:
6.2.1.3.1 Frequencies should be deployed having regard to the rated coverage of the NDBs concerned, so that the ratio
of the signal strength of any NDB at the boundary of its rated coverage to the total field strength due to co-channel stations
and adjacent channel stations (with an appropriate allowance for the selectivity characteristics of a typical airborne receiver)
is not less than 15 dB by day.
6.2.1.3.2 The figures set forth in Attachment B to Volume V of Annex 10 should be applied, as appropriate, in
determining the allowance to be made for the attenuation of adjacent channel signals.
6.2.1.4 It follows from the application of rated coverage to frequency deployment planning that, unless otherwise
specified, protection against harmful interference can only be ensured within the rated coverage of an NDB and, then, only if
the radiated power of the NDBs is adjusted to provide within reasonably close limits the field strength required at the limit of
the rated coverage. In areas where the density of NDBs is high, any NDB providing a signal at the limit of its rated coverage
materially in excess of that agreed in the region concerned will give rise, in general, to harmful interference within the rated
coverages of cochannel or adjacent channel NDBs in the area concerned, and will limit the number of NDBs which can be
installed in the region within the available spectrum. It is important, therefore, that increases in radiated power beyond that
necessary to provide the rated coverage, particularly at night when sky wave propagation may give rise to interference over
long distances, should not be made without coordination with the authorities of the other stations likely to be affected (see
Chapter 3, 3.4.3).
6.2.1.5 Frequency planning is considerably facilitated if a common value of minimum field strength within the desired
coverage is used.
6.2.1.6 Extensive experience has shown that in relatively low noise level areas, such as Europe, the figure of
70 microvolts per metre is satisfactory.
6.2.1.6.1 Experience has also shown that the figure of 120 microvolts per metre is generally satisfactory for higher
noise level areas but will be inadequate in areas of very high noise. In such areas, the information given in 6.3 may be used
for general guidance.
ATT C-59 23/11/06
Annex 10 — Aeronautical Communications Volume I
6.2.2 Relationship to effective coverage
6.2.2.1 Rated coverage may have a close correlation to effective coverage under the following conditions:
a) when the minimum field strength within the rated coverage is such that, for most of the time, it exceeds the field
strength due to atmospheric and other noise sufficiently to ensure that the latter will not distort the information
presented in the aircraft to the extent that it is unusable;
b) when the ratio of the strength of the wanted signal to that of interfering signals exceeds the minimum required value
at all points within the coverage, in order to ensure that interfering signals will also not distort the information
presented in the aircraft to the extent that it is unusable.
6.2.2.2 Since, normally, the lowest signal within the coverage will occur at its boundary, these conditions imply that at
the boundary the field strength should be such that its ratio to atmospheric noise levels would ensure usable indications in the
aircraft for most of the time and that, in respect of the boundary value, overall planning should ensure that the ratio of its
value to that of interfering signals exceeds the required value for most of the time.
6.2.2.3 Although the value of 70 microvolts per metre used for frequency deployment has been found successful in
Europe (i.e. north of 30° latitude) in giving coverage values which closely approximate to effective coverage most of the time,
experience is too limited to prove the suitability of the 120 microvolts per metre value for general application in areas of high
noise. It is to be expected that rated coverages in high noise based on a boundary value of 120 microvolts per metre will, on
many occasions, be substantially greater than the effective coverage achieved. In such areas, in order to secure a better
correlation between rated coverage and an average of the achieved effective coverage, it may be advisable to choose a
boundary value based more closely on the proportionality of noise in that area to the noise in areas where a boundary value
has been satisfactorily established (e.g. Europe), or to determine an appropriate value from a statistical examination of
achieved effective coverages in respect of an NDB in the area of known performance.
6.2.2.4 It is important to appreciate, however, that minimum values of field strength based on a simple comparison of
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