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±3 (±10)
±6 (±20)
±3 (±10)
±3 (±10)
±3 (±10)
±6 (±20)
±37 (±121)
±37 (±121)
±3 (±10)
±6 (±20)
±20 (±66)
±20 (±66)
±3 (±10)
±6 (±20)
Note 1.— The figures for “non-specular multipath” and for “garble” are the totals of the up-link and down-link
components.
Note 2.— PFE contains both bias and time varying components. In the above table the time varying components and
most site related errors are assumed to be essentially statistically independent. The bias components may not conform to any
particular statistical distribution.
In considering these error budgets, caution is to be exercised when combining the individual components in any
particular mathematical manner.
Note 3.— The transmitter wave form is assumed to have a 1 200 nanosecond rise time.
ATT C-77 23/11/06
Annex 10 — Aeronautical Communications Volume I
7.3.4 System implementation
7.3.4.1 While the DME/P may be implemented in various ways, the instrumental and propagation errors assumed are
typical of those obtainable with equipment designs which provide internal time delay drift compensation and which establish
timing reference points by thresholding on the leading edge of the first pulse of a pulse pair using the following techniques:
a) IA mode. A conventional technique which thresholds at the 50 per cent amplitude point;
b) FA mode. A delay-attenuate-and-compare (DAC) technique which thresholds between the 5 per cent and 30 per cent
amplitude points.
7.3.4.2 Accuracy standard 1 can be achieved using a delay of 100 nanoseconds and an attenuation of 5 to 6 dB. It is
also required that the threshold amplitude point of both the delayed pulse and the attenuated pulse lie within the partial rise
time region.
7.3.4.3 The example above does not preclude time of arrival measurement techniques other than the DAC from being
used, but it is necessary in any case that threshold measurements take place during the pulse partial rise time.
7.3.5 DME/P interrogator signal processing
7.3.5.1 During acquisition
a) The interrogator acquires and validates the signal within 2 seconds before transitioning to track mode even in the
presence of squitter and random pulse pairs from adjacent channels, which result in a 50 per cent system efficiency.
b) After loss of the acquired signal in either the IA or FA mode, the interrogator provides a warning output within
1 second, during which time the guidance information continues to be displayed. After loss of signal, the
interrogator returns to the search condition in the IA mode in order to re-establish track.
7.3.5.2 During track
When track is established, the receiver output consists of valid guidance information before removing the warning. The
validation process continues to operate as long as the interrogator is in track. The interrogator remains in track as long as the
system efficiency is 50 per cent or greater. While in track, the receiver provides protection against short duration, large
amplitude erroneous signals.
7.3.5.3 Range date filter
The accuracy specifications in Chapter 3, 3.5.3.1.3.4, as well as the error budgets discussed in 7.3.3, assume that the
higher frequency noise contributions are limited by a low pass filter with a corner frequency of qw as specified in
Figure C-21. Depending upon the user’s application, additional filtering for noise reduction can be used provided that the
induced phase delay and amplitude variation do not adversely affect the aircraft flight control system’s dynamic response.
The following sections recommend additional features which should be incorporated into the data filter.
7.3.5.4 Velocity memory
The data filter may require a velocity memory in order to achieve the specified accuracies in Chapter 3, 3.5.3.1.3.4 with a
system efficiency of 50 per cent. It should be noted that low system efficiencies can occur in the IA mode during
identification transmissions.
23/11/06 ATT C-78
Attachment C Annex 10 — Aeronautical Communications
DME/P
INTERROGATOR
RAW
DISTANCE
ESTIMATES
RECEIVER
OUTPUT
FILTER 2
ABSOLUTE
POSITION
REFERENCE
PATH
FOLLOWING
ERROR
FILTER 0
PATH
FOLLOWING
ERROR
CONTROL
MOTION NOISE
FILTER 1
CONTROL
MOTION
NOISE
A
B
+-
GUIDANCE
FUNCTION
DME/P
CORNER FREQUENCIES (RADIANS/SEC)
1.5 0.5 10
0 1 2*
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