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combined linearly. The amplitude and phase masks that the
100 per cent raised cosine pulse shaping filter must satisfy are
shown in Figures A-6 and A-7 of this guidance material, while
those of the 60 per cent root raised cosine filter are shown in
Figures A-23 and A-24. These correspond to the transmit filter
requirements given in the definition of A-QPSK. Those
requirements apply to the transmitted signal before it
undergoes any non-linear amplification; their purpose is to
limit and control the distortion and ccrresponding degradation
in performance caused by non-linear amplification. There is no
requirement for actual modulators to be implemented in this
way, as long as the modulated RF signal is indistinguishable
from one that was generated by an ideal modulator.
3.2 Bounds on radiated power
spectral density
3.2.1 Spectrum masks. These spectrum masks allow for
degradation from the ideal Nyquist model that could occur due
to non-ideal system characteristics, e.g. saturation in the
amplifier chain.
3.2.2 Fmm-aircmfr. The spectral mask that must be
satisfied by any A-BPSK signal transmitted in the fromaircraft
direction is shown in Figure A-8 of this guidance
material. This mask is applicable for 100 per cent root raised
cosine filtering. This was derived assuming a non-linear
amplifier (Class C) is used on board the AES, but it is
applicable to Class A linear amplifiers as well. The same
spectral mask (Figure A-8) applies to A-QPSK. The spectral
mask (Figure A-22) applies to A-QPSK with a 60 per cent root
raised cosine filter.
3.2.3 To-aircrafl. The spectral mask that must be met in
the to-aircraft direction with A-BPSK is shown in Figure A-9
of this guidance material. This was derived assuming that all
amplifiers in the to-aircraft transmission path are operating
linearly. The corresponding spectral mask for A-QPSK is
shown in Figure A-10 of this guidance material.
211YOO
No. 75

　
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