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Initiation of the turn-on process shall not commence sooner than 1 microsecond prior to the virtual origin.
Note 1.— The time “during the pulse” encompasses the total interval from the beginning of pulse transmission to its end.
For practical reasons, this interval may be measured between the 5 per cent points on the leading and trailing edges of the
pulse envelope.
Note 2.— The power contained in the frequency bands specified in 3.5.4.1.3 e) and f) is the average power during the
pulse. Average power in a given frequency band is the energy contained in this frequency band divided by the time of pulse
transmission according to Note 1.
3.5.4.1.4 Pulse spacing
3.5.4.1.4.1 The spacing of the constituent pulses of transmitted pulse pairs shall be as given in the table in 3.5.4.4.1.
3.5.4.1.4.2 DME/N. The tolerance on the pulse spacing shall be plus or minus 0.25 microsecond.
3.5.4.1.4.3 DME/N. Recommendation.— The tolerance on the DME/N pulse spacing should be plus or minus
0.10 microsecond.
3.5.4.1.4.4 DME/P. The tolerance on the pulse spacing shall be plus or minus 0.10 microsecond.
3.5.4.1.4.5 The pulse spacings shall be measured between the half voltage points on the leading edges of the pulses.
3.5.4.1.5 Peak power output
3.5.4.1.5.1 DME/N. Recommendation.— The peak effective radiated power should not be less than that required to
ensure a peak pulse power density of approximately minus 83 dBW/m2 at the maximum specified service range and level.
‡3.5.4.1.5.2 DME/N. The peak equivalent isotropically radiated power shall not be less than that required to ensure a
peak pulse power density of minus 89 dBW/m2 under all operational weather conditions at any point within coverage
specified in 3.5.3.1.2.
Note.— Although the Standard in 3.5.4.1.5.2 implies an improved interrogator receiver sensitivity, it is intended that the
power density specified in 3.5.4.1.5.1 be available at the maximum specified service range and level.
3.5.4.1.5.3 DME/P. The peak equivalent isotropically radiated power shall not be less than that required to ensure the
following peak pulse power densities under all operational weather conditions:
a) minus 89 dBW/m2 at any point within the coverage specified in 3.5.3.1.2 at ranges greater than 13 km (7 NM) from
the transponder antenna;
b) minus 75 dBW/m2 at any point within the coverage specified in 3.5.3.1.2 at ranges less than 13 km (7 NM) from the
transponder antenna;
c) minus 70 dBW/m2 at the MLS approach reference datum;
Annex 10 — Aeronautical Communications Volume I
23/11/06 3-46
d) minus 79 dBW/m2 at 2.5 m (8 ft) above the runway surface, at the MLS datum point, or at the farthest point on the
runway centre line which is in line of sight of the DME transponder antenna.
Note.— Guidance material relating to the ERP may be found in Attachment C, 7.2.1 and 7.3.8.
3.5.4.1.5.4 The peak power of the constituent pulses of any pair of pulses shall not differ by more than 1 dB.
3.5.4.1.5.5 Recommendation.— The reply capability of the transmitter should be such that the transponder should be
capable of continuous operation at a transmission rate of 2 700 plus or minus 90 pulse pairs per second (if 100 aircraft are
to be served).
Note.— Guidance on the relationship between number of aircraft and transmission rate is given in Attachment C, 7.1.5.
3.5.4.1.5.6 The transmitter shall operate at a transmission rate, including randomly distributed pulse pairs and
distance reply pulse pairs, of not less than 700 pulse pairs per second except during identity. The minimum transmission
rate shall be as close as practicable to 700 pulse pairs per second. For DME/P, in no case shall it exceed 1 200 pulse pairs
per second.
3.5.4.1.6 Spurious radiation. During intervals between transmission of individual pulses, the spurious power received
and measured in a receiver having the same characteristics as a transponder receiver, but tuned to any DME interrogation or
reply frequency, shall be more than 50 dB below the peak pulse power received and measured in the same receiver tuned to
the reply frequency in use during the transmission of the required pulses. This provision refers to all spurious transmissions,
including modulator and electrical interference.
‡3.5.4.1.6.1 DME/N. The spurious power level specified in 3.5.4.1.6 shall be more than 80 dB below the peak pulse
power level.
3.5.4.1.6.2 DME/P. The spurious power level specified in 3.5.4.1.6 shall be more than 80 dB below the peak pulse
power level.
3.5.4.1.6.3 Out-of-band spurious radiation. At all frequencies from 10 to 1 800 MHz, but excluding the band of
frequencies from 960 to 1 215 MHz, the spurious output of the DME transponder transmitter shall not exceed minus 40 dBm
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