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The effective radiated power contained in the 0.5 MHz measurement frequency band specified in 3.5.4.1.3 e) can be
calculated by integrating the power spectral density in the frequency domain or equivalently by integrating the instantaneous
power per unit time in the time domain using the appropriate analogue or digital signal processing techniques. If the
integration is performed in the frequency domain then the resolution bandwidth of the spectrum analyser must be
commensurate with the 5 per cent duration interval of the DME pulse. If the integration is performed in the time domain at
the output of a 0.5 MHz five pole (or more) filter then the time sample rate must be commensurate with the pulse spectrum
width.
7.1.12 Special considerations for DME/P associated with ILS
7.1.12.1 For those runways where it is intended to install DME associated with ILS and where early MLS/RNAV
operations are planned, installation of DME/P is preferred.
7.1.12.2 When it is intended to use the DME/P ranging information throughout the terminal area, interrogation pulse
pairs with the correct spacing and nominal frequency must trigger the transponder if the peak power density at the transponder
antenna is at least minus 93 dBW/m2. This sensitivity level is based on the values contained in Chapter 3, 3.5.4.2.3.1
and it is applied to DME/P IA mode, where at this level DME/P IA mode is intended to comply with DME/N reply efficiency
and at least DME/N accuracy.
23/11/06 ATT C-72
Attachment C Annex 10 — Aeronautical Communications
ATT C-73 23/11/06
7.2 Guidance material concerning DME/N only
7.2.1 Effective radiated power (ERP) of DME/N facilities
7.2.1.1 The power density figure prescribed in 3.5.4.1.5.1 of Chapter 3 is on the following assumptions:
Airborne receiver sensitivity –112 dBW
Airborne transmission line loss +3 dB
Airborne polar pattern loss
relative to an isotopic antenna +4 dB
Necessary power at antenna –105 dBW
Minus 105 dBW at the antenna corresponds to minus 83 dBW/m2 at the mid-band frequency.
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.
7.2.1.2 Nominal values of the necessary ERP to achieve a power density of minus 83 dBW/m2 are given in Figure C-20.
For coverage under difficult terrain and siting conditions it may be necessary to make appropriate increases in the ERP.
Conversely, under favourable siting conditions, the stated power density may be achieved with a lower ERP.
7.2.1.3 The use of Figure C-20 is illustrated by the following examples. In order to achieve the necessary nominal
power density at slant range/levels of 342 km (185 NM)/12 000 m (40 000 ft), 263 km (142 NM)/12 000 m (40 000 ft) and
135 km (73 NM)/6 000 m (20 000 ft), ERPs of the order of plus 42 dBW, plus 36 dBW and plus 30 dBW respectively would
be required.
7.3 Guidance material concerning DME/P only
7.3.1 DME/P system description
7.3.1.1 The DME/P is an integral element of the microwave landing system described in Chapter 3, 3.11. The DME/P
signal format defines two operating modes, initial approach (IA) and final approach (FA). The IA mode is compatible and
interoperable with DME/N and is designed to provide improved accuracies for the initial stages of approach and landing. The
FA mode provides substantially improved accuracy in the final approach area. Both modes are combined into a single
DME/P ground facility and the system characteristics are such that DME/N and DME/P functions can be combined in a
single interrogator. The IA and FA modes are identified by pulse codes which are specified in Chapter 3, 3.5.4.4. In the MLS
approach sector, the DME/P coverage is at least 41 km (22 NM) from the ground transponder. It is intended that the
interrogator does not operate in the FA mode at ranges greater than 13 km (7 NM) from the transponder site, although the
transition from the IA mode may begin at 15 km (8 NM) from the transponder. These figures were selected on the
assumption that the transponder is installed beyond the stop end of the runway at a distance of approximately 3 600 m (2 NM)
from the threshold.
Annex 10 — Aeronautical Communications Volume I
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)
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