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(RLOS) separation criteria (whichever is smaller) may
be used.
Note.- Guidance material relating to the establishment of
the minimum separation distance based on the desired to
undesired signal protection ratio of 14 dB is contained in
Attachment A.
4.1.5.2 In the case of those VHF facilities providing
service beyond the radio horizon, except where there is an
operational requirement for the use of common frequencies for
groups of facilities, planning for co-channel operations shall
be such that points at the protection heights and at the limits
of the functional service area of each facility are separated by
distances not less than the sum of distances from each point to
its associated radio horizon.
Note 1.- The distance to the radio horizon from a station
in an aircraft is normally given by the formula:
where D = distance in nautical miles;
h = height of the aircraft station above earth;
K = (corresponding to an effective earth's radius
of 4/3 of the actual radius);
= 2.22 when h is expressed in metres; and
= 1.23 when h is expressed in feet.
Note 2.- In calculating the radio line-of-sight distance
between a ground station and an aircraft station, the distance
from the radio horizon of the aircraft station computed from
Note I must be added to the distance from the radio horizon
of the ground station. In calculating the latter the same
formula is employed, taking for h the height of the ground
station transmitting antenna.
Note 3.- The criterion contained in 4.1.5.2 is applicable in
establishing minimum geographical separation between VHF
facilities, with the object of avoiding co-channel air-to-air
interference. Guidance material relating to the establishment
of separation distances between ground stations and between
aircraft and ground stations for co-channel operations is
contained in Section 3 of Attachment A. Guidance material
relating to adjacent channel frequency deployment is
contained in Section 2 of Attachment A.
Note 4.- Guidance material on the interpretation of 4.1.5.1
and 4.1.5.2 is contained in Attachment A.
4.1.5.3 The geographical separation between facilities
working on adjacent channels shall be such that points at the
protection heights and at the limit of the functional service
range of each facility are separated by a distance sufficient to
ensure operations free from harmful interference.
Note.- Guidance material covering separation distances
and related system characteristics is contained in Attachment A.
4.1.5.4 The protection height shall be a height above a
specified datum associated with a particular facility, such that
below it harmful interference is improbable.
4.1.5.5 The protection height to be applied to functions or
to specific facilities shall be determined regionally, taking into
consideration the following factors:
a) the nature of the service to be provided;
b) the air traffic pattern involved;
c) the distribution of communication traffic;
d) the availability of frequency channels in airborne equipment;
e) probable future developments.
4.1.5.6 Recommendation.- Where the protection
heights determined are less than those operationally desirable,
separation between facilities operating on the same frequency
should not be less than that necessary to ensure that an
aircraft at the limit of the functional service range and the
operationally desirable protection height of one facility does
not come above the radio horizon with respect to adjacent
facilities.
Note.- The effect of this recommendation is to establish a
geographical separation distance below which harmful interference
is probable.
4.1.5.7 The geographical separation between VHF
VOLMET stations shall be determined regionally and,
generally, shall be such that operations free from harmful
interference are secured at the highest altitude flown by
aircraft in the area concerned.
Note.- Guidance material on the interpretation of 4.1.5.7
is contained in Attachment A.
4.1.5.8 Frequencies in the aeronautical mobile VHF band
used for national services, unless worldwide or regionally
allotted to this specific purpose, shall be so deployed that
minimum interference is caused to facilities for the
international air services in this band.
4.1.5.9 Recommendation.- The problem of inter-State
interference on frequencies allotted worldwide or on a
regional basis to national services, should be resolved by
consultation between the administrations concerned.
4.1.5.10 The communication coverage provided by a
VHF ground transmitter shall, in order to avoid harmful
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