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Power required at antenna –110 dBW
The power required of minus 100 dBW is obtained at 118 MHz with a power density of minus 107 dBW/m2; minus
107 dBW/m2 is equivalent to 90 microvolts per metre, i.e. plus 39 dB referenced to 1 microvolt per metre.
Note.— The power density for the case of an isotropic antenna may be computed in the following manner:
2
10 log
Pd Pa 4
λ
= −
π
where
Pd = power density in dBW/m2;
Pa = power at receiving point in dBW;
λ = wavelength in metres.
3.1.2 Nominal values of the necessary ERP to achieve a field strength of 90 microvolts per metre (minus 107 dBW/m2)
are given at Figure C-13. For coverage under difficult terrain and siting conditions, it may be necessary to make appropriate
increases in the effective radiated power. Conversely, practical experience has shown that under favourable siting conditions,
and under the less pessimistic conditions often found in actual service, satisfactory system operation is achieved with a lower
ERP.
Note.— The nominal effective radiated powers, expressed as a function of level and range, are based upon consideration
of basic theoretical data from various sources (such as ITU-R and NBS) modified empirically to reflect typical operational
experience.
3.1.3 The use of Figure C-13 is illustrated by the following examples. In order to achieve the necessary field strength at
342 km (185 NM)/12 000 m (40 000 ft), 300 km (162 NM)/12 000 m (40 000 ft), and 166.5 km (90 NM)/6 000 m (20 000 ft),
nominal effective radiated powers of plus 23 dBW, plus 17 dBW and plus 11 dBW respectively are required.
3.1.4 In order to facilitate frequency and equipment planning, wherever practicable, ERP categories corresponding to
plus 23 dBW, plus 17 dBW and plus 11 dBW should be employed. These ERP values should be indicated during regional
planning activities.
23/11/06 ATT C-42
Attachment C Annex 10 — Aeronautical Communications
25
(46)
50
(93)
75
(139)
100
(185)
125
(232)
150
(278)
175
(324)
200
(371)
NM
(km)
3 000
(10 000)
6 000
(20 000)
9 000
(30 000)
12 000
(40 000)
15 000
(50 000)
Metres
(feet)
Nominal VOR effective radiated power required
to provide –107 dBW/m power density, 90 microvolts
per metre field strength, at various slant
ranges/levels with a typical antenna array
located 4.9 m (16 ft) above ground
2
Level above facility
Slant range distance from VOR antenna
11 dBW
17 dBW
23 dBW
Note 1.— These curves are based on extensive
experience of a number of facilities and indicate the
nominal effective radiated power to assure the
specified power density on a high percentage of
occasions taking into account propagation and
typical ground/aircraft installation characteristics.
0
0
Note 2.— These curves display coverage versus power only. For frequency planning guidance, refer to 3.4 of Attachment C.
Figure C-13
ATT C-43 23/11/06
Annex 10 — Aeronautical Communications Volume I
3.1.5 A VOR having an ERP of plus 23 dBW approximates to a VOR previously referred to in Annex 10 as
Category A (transmitter power 200 W). Possible relationships between ERP and transmitter output powers are illustrated by
the following examples:
Example I Example II
Transmitter power +23 dBW +18 dBW
Ground transmission line loss –2 dB –1 dB
Antenna gain relative to an isotropic antenna +2 dB +6 dB
ERP +23 dBW +23 dBW
Similarly, a VOR having an ERP of plus 17 dBW approximates to a VOR previously referred to in Annex 10 as Category B
(transmitter power 50 W). Possible relationships between ERP and transmitter output powers are illustrated by the following
examples:
Example I Example II
Transmitter power +17 dBW +10 dBW
Ground transmission line loss –2 dB –1 dB
Antenna gain relative to an isotropic antenna +2 dB +8 dB
ERP +17 dBW +17 dBW
3.1.6 It is recognized that the above ERP categories may achieve a greater coverage than is necessary for some
operational requirements. A suitable lesser coverage might be achieved by a VOR facility having an ERP of approximately
plus 11 dBW as follows:
Example I Example II
Transmitter power +11 dBW +7 dBW
Ground transmission line loss –2 dB –1 dB
Antenna gain relative to an isotropic antenna +2 dB +5 dB
ERP +11 dBW +11 dBW
3.2 Guidance in respect of siting of VOR
3.2.1 The site should be on the highest ground in the vicinity to obtain the greatest line-of-sight coverage and should be
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