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2) the currents in the radiating elements of a particular dipole array are equal and in time phase.
b) Counterpoise. A square counterpoise with minimum dimensions of 9 m × 9 m, usually elevated about 1.8 m (6 ft)
above the ground and, if fabricated from wire mesh, with the dimension of the mesh not exceeding 7.5 cm × 7.5 cm.
ATT C-57 23/11/06
Annex 10 — Aeronautical Communications Volume I
5.1.3 Fan marker beacons for use only at low altitudes (low power fan marker beacons). A radiating system capable of
providing the field strengths indicated in Chapter 3, 3.1.7.3.2.
5.1.4 Fan marker beacons for general use (high power fan marker beacons)
a) Radiating system. A radiating system consisting of four horizontal co-linear half-wave (approximate) radiating
elements mounted approximately one-quarter wavelength above the counterpoise. The current in each of the antenna
elements should be in phase and should have a current ratio of 1:3:3:1.
Note.— The current distribution between elements and their height above the counterpoise may be altered to
provide patterns for specific operational requirements. Improved vertical patterns for certain operational needs may
be achieved by adjusting the height of the dipole arrays above the counterpoise to a value of one-quarter
wavelength or greater, but less than a half wavelength.
b) Counterpoise. A rectangular counterpoise with minimum dimensions of 6 m × 12 m, usually elevated about 1.8 m
(6 ft) above the ground and, if fabricated from wire mesh, with the dimension of the mesh not exceeding
7.5 cm × 7.5 cm.
5.2 Identification coding for fan marker beacons
associated with a four-course radio range
5.2.1 Fan marker beacons located on the legs of a four-course radio range do not normally require an identification
signal relating to a particular geographic location, but only a signal that will indicate the leg with which they are associated.
5.2.2 In the case of a four-course radio range having not more than one marker on any leg, it is current practice to
identify a marker by a single dash if on the leg bearing true north or nearest to north in a clockwise direction (east), and to
identify a marker on other legs by two, three or four dashes according to whether the leg with which it is associated is the
second, third or fourth leg from north in a clockwise direction. Where more than one fan marker beacon is associated with
one leg of a four-course radio range, the marker nearest to the station is identified by dashes only, the next nearest by two
dots preceding the dashes, and the third by three dots preceding the dashes, and so on.
Note.— In certain special circumstances, the above coding system may lead to ambiguities due to two markers
associated with the legs of different but overlapping radio ranges being geographically close together. In such cases, it is
desirable to use a distinctive identification coding with one of the marker beacons.
6. Material concerning NDB
6.1 Guidance material on NDB field strength requirements
in latitudes between 30°N and 30°S
6.1.1 In order to obtain a satisfactory service within the rated coverage of an NDB located in latitudes between 30°N
and 30°S, a minimum value of field strength of 120 microvolts per metre would be required, except where practical
experience in the operation of NDBs over several years has revealed that a minimum field strength of 70 microvolts per
metre would be adequate to meet all the operational needs. In some specific areas, field strength values considerably in
excess of 120 microvolts per metre would be required. Such areas are:
a) Indonesia and Papua New Guinea, Myanmar, Malay Peninsula, Thailand, Lao People’s Democratic Republic,
Democratic Kampuchea, Viet Nam and Northern Australia;
23/11/06 ATT C-58
Attachment C Annex 10 — Aeronautical Communications
b) Caribbean and northern parts of South America;
c) Central and South Central Africa.
6.1.2 The field strength of 120 microvolts per metre is based upon practical experience to date and is a compromise
between what is technically desirable and what it is economically possible to provide.
6.2 Guidance material on meaning and application
of rated and effective coverage
6.2.1 Rated coverage
6.2.1.1 The rated coverage as defined in Chapter 3, 3.4.1, is a means of designating actual NDB performance, in a
measurable way, which is dependent on the frequency, the radiated power, and the conductivity of the path between the NDB
and a point on the boundary where the minimum value of field strength is specified.
6.2.1.2 The rated coverage has been found to be a useful means of facilitating regional planning and, in some instances,
may be related to effective coverage.
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