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4.2.1.5.1 The channel number (Ct) shall be defined with
respect-to the centre frequency on the to-aircraft transmission
path by the formula:
Ct =
frequency of transmission (MHz) - 1 510.0
0.0025
4.2.1.5.2 The channel number (Ct) shall be defined with
respect to the centre frequency on the from-aircraft
transmission path by the formula:
,- f requency of transmission (MHz) - 1 6 11.5
4.2.2 Frequency accuracy
The frequency of transmission from the aircraft earth station,
as would be received at the satellite, shall not vary from the
nominal channel frequency by more than 2383 Hz due to all
causes.
Part I Annex 10 - Aeronautical Telecommunications
Note.- The frequency of Fransmissions received by a
subsonic aircraft should not vary from the nominal channel
frequency by more than k2.18 kHz due to ull causes.
4.2.3 Aircraft earth stations
RF characteristics
Note.- The following requirements apply over the entire
transmit and receive frequency bunds.
4.2.3.1 GENERALAN TENNA
CHARACTERISTICS
4.2.3.1.1 Reference coverage volume. Antenna systems
shall be installed to meet performance requirements for
transmitting and receiving over a coverage volume of 360
degrees of azimuth and from 5 to 90 degrees in elevation from
a horizontal plane for aircraft in straight and level flight.
4.2.3.1.1.1 Recommendation.- To the maximum extent
possible, antenna systems should be installed to meet
pe$omzance requirements for trartsmitting and receiving over
a coverage volume of 360 degrees in azimuth and from 5 to
90 degrees in elevation from a horizontal plane for aircraft
uttirudes of +20/-5 degrees of pitch and *25 degrees of roll.
4.2.3.1.2 Polarization. The polarization shall be righthand
circular for both receiving and transmitting,,in _accordance
with the definition of CCIR Recommendation 573.
4.2.3.1.3 Antenna switching. Aircraft earth stations that
require more than one antenna shall be capable of switching
from one antenna to another in the same antenna sub-system
so as to introduce a signal interruption of not more than
40 ms.
Note.- 4.2.3.2 and 4.2.3.3 outline the requirements for
high gain and low gain antennas only. This does not preclude
the future introduction. of mid-gain antennas; however; some
of the considerations which must be mde before such un
introduction are described in the guidance material contained
in Attachment A to Part I qf Anne-x 10, Volunle Ill.
4.2.3.2 LOW GAIN ANTENNA
SUB-SYSTEMS
4.2.3.2.1 Gain-to-noise temperature ratio. Receiving
sub-systems employing low gain antennas shall achieve againto-
noise temperature ratio (G/T) of not less than -26 dB/K
over not less than 85 per cent of the reference coverage
volulne defined in 4.2.3.1.1 ; and not less than -3 1 dB/K over
the remaining 15 per cent of the reference coverage volume.
The only exception to this is the region greater than 70
degrees in elevation from the horizontal plane where the G/I
may be not less than -28 dB/K.
4.2.3.2.2 Axial ratio. The axial ratio shall be less than
6 dB for elevation angles of 45 to 90 degrees and less than
20 dB for elevation angles of 5 to 45 degrees or the AES
antenna shall have sufficient gain to compensate for additional
polarization loss in excess of that caused by the axial ratios.
The condition for including the compensation shall assume the
satellite axial ratio to be 2.5 dB, with major axes of the
polarization ellipses orthogonal.
4.2.3.2.3 Recommendation.- To the maximum extent
possible, the G/T should be not less than -26 dB/K and the
axial ratio should be less than 6 dB over 100 per cent of the
reference coverage volume.
4.2.3.3 HIGH GAIN ANTENNA
SUB-SYSTEMS
4.2.3.3.1 Gain-to-noise temperature ratio. Receiving'
sub-systems employing high gain antennas shall achieve a
gain-to-noise temperature ratio (G/T) of not less than -13
dBK over not less than 75 per cent of the reference coverage
volume and shall be not less than -25 dB/K over the remaining
25 per cent of the reference coverage volume defined in .
4.2.3.1.1.
4.2.3.3.2 Axial ratio. The axial ratio shall be less than
6 dB over the 75 per cent of the reference coverage, volume
referred to in 4.2.3.3.1 where the G/T must exceed -13 dB/K
or the AES antenna shall have sufficient gain to compensate
for additional polarization loss in excess of that caused by this
axial ratio. The condition for including the compensation shall
assume the satellite axial ratio to be 2.5 dB, with the major
axes of the polarization ellipses orthogonal.
4.2.3.3.3 Recommendation.-- To the maximum extent
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