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network userentity of the aircraft ATN intermediate system.
If the provision of a VHF subnetwork service to an ATN
intermediate system were considered an essential service for
a particular installation, the VDL functionality of the VDR
would need to be certified as an essential function. The use of
VDL for ATS communications is not, however, intended to
require two aircraft radios to operate simultaneously in M L
mode.
5.3 Registmtion of aircraft with
VDL network operators .
5.3.1 For normal communications service, it is to be
expected that aircraft operators will. be requiied to register
their aircraft with the network operators. In emergency or
back-up situations, it must be- possible for any VDL-equipped
aircraft to establish connectivity over any VDL ground station
network.
5.3.2 Registration of. aircraft VDL stations with VDL
network operators is desirable for network management since,
,for example, a network operator may identify a temporary
fault in the VDL communicatims from an aircraft and would
wish to contact the operator of the aircraft in order to have the
fault resolved. Registration of aircraft is also useful in
planning the required ground station network capacity. Registration
with a VDL.gmund station network operator does not
necessarily imply that the aircraft operator will be charged for
use of the VDL ground station network.
Annex 10 - AeronrruticaI Telecommunic&'ons
FIGURE FOR ATTACHMENT B
VDL subnetwork
Figure B-1
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ATTACHMENT A TO PART 11. GUIDANCE MATERIAL
FOR COMMUNICATION SYSTEMS
1. VHF COMMUNICATIONS
1.1 Audio characteristics of VHF
communication equipment
1.1.1 The aeronautical radiotelephony services represent
a special case of the application of radiotelephony, in that the
requirement is for the transmission of messages in such a way
that fidelity of wave form is of secondary importance,
emphasis being upon fidelity of basic intelligence. This means
that it is not necessary to transmit those parts of the wave
form which are solely concerned with individuality, accent and
emphasis.
1.1.2 The effective acceptance bandwidth for 8.33 kHz
equipment is required to be at least plus and minus 3 462 Hz.
This value considers the general case, i.e. air-to-ground
transmissions and consists of 2 500 Hz audio bandwidth,
685 Hz for an aircraft transmitter instability of 5 ppm, 137 Hz
for a ground receiver instability of 1 ppm and 140 Hz due to
Doppler shift (2.2.2.4 and 2.3.2.6 of Part I1 refer).
1.2 Off-set carrier system
The following are examples of offset cartier systems which
meet the requirements of Part 11, 2.2.1.1.1.
a) 2-carrier system. Carriers should be spaced at plus and
minus 5 kHz. This requires a frequency stability of
plus or minus 2 kHz (15.3 parts per million at
130 MHz).
b) 3-carrier system Carriers should be spaced at zero and
plus and minus 7.3 kHz. This requires a frequency
stability of plus or minus 0.65 kHz (5 parts per million
at 130 MHz).
The following are examples or 4- and 5-carrier systems
which meet the requirements of Part 11, 2.2.1 .I .l.
c) 4-carrier system. Carriers should be spaced at plus and
minus 2.5 kHz and plus and minus 7.5 kHz. This
requires a frequency stability of plus or minus 0.5 kHz
(3.8 parts per million at 130 MHz).
d) 5-carrier system. Carriers should be spaced at zero,
plus and minus 4 kHz and plus and minus 8 kHz. A
frequency stability in the order of plus or minus 40 Hz
(0.3 parts per million at 130 MHz) is an achievable
and practicable interpretation of the requirement in this
case.
Note 1.- The carrierfiequency spacings referred to above
am with respect to the assigned channel frequency.
Note 2.- In aircraft receivers which employ a measurement
of the received carrier-to-noise ratio to operate the mute,
the audio heterodynes caused by the reception of two or more
off-set carriers can be interpreted as noise and cause the
audio output to be muted even when an adequate wanted
signal is present. In order that the airborne receiving system
can conform with the sensitivity recommendations contained
in Part 11, 2.3.2.2, the design of the receivers may need to
ensure that their sensitivity is maintained ot a high level when
receiving off--set carrier transmissions. The use of a carrier
level override is an unsatisfactory solution to this requirement,
but where it is employed, setting the override level as low as
possible can ameliorate the problem.
1.3 Immunity performance of COM
receiving systems in the presence of
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