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assumed:
a) an 8.33 kHz channel, which is assigned 8.33 kHz
away from the assigned frequency of a 25 kHz
channel, is assumed to be co-channel with that
25 kHz channel;
b) an 8.33 kHz channel, spaced *16.67 kHz from the
assigned frequency of a 25 kHz channel is assumed
under all operating conditions (including all instabilities
and doppler shifts), to have an adjacent channel
rejection ratio of:
i) 23 dB aircraft against ground offset carrier systems;
ii) 30 dB aircraft against ground non-offset carrier
systems; and
84 NM aircraft against ground non-offset carrier
systems; and
118 NM aircraft against aircraft systems.
ii) Desired-to-undesired signal ratio.
The minimum distance required to provide sufficient
adjacent channel protection based upon a D/U ratio
(assuming equal ERP from the wanted and unwanted
signals) can be calculated given the maximum service
range of the wanted signal by:
Dadj = service rangel(l0 (ACR - D/U)/20)
Dadj = distance required between the edges of the
two service ranges operating on adjacent
channels
ACR = adjacent channel rejection
Dadj and service range expressed in the same units.
iii) 27 dB aircraft against aircraft systems.
Worst case conditions for planning purposes are used
here for a mixed environment of 8.33 kHz and 25 kHz
systems.
c) an 8.33 kHz channel which is assigned 25 kHz away
from the assigned frequency of a 25 kHz channel is
assumed to have an effective adjacent channel characteristic
of at least 60 dB.
2.5.2 Where it is necessary to take account of
the implementation of VHF stations which use 8.33 kHz
channel spacing,' in a region where 25 kHz assignments
occur, the assumptions of 2.5.1 a) to c) result in the
following:
a) where 8.33 kHz services are spaced e8.33 kHz away
from the assigned frequency of a 25 kHz channel, the
regionally agreed planning criteria for co-channel
assignments should be used, applying either the radio
horizon method (assumed to give at least 20 dB Dm) or
a desired-to-undesired signal ratio of 14 dB;
b) where 8.33 kHz services are spaced 216.67 kHz away
from the assigned frequency of a 25 kHz channel, the
following criteria should be applied:
i) Receiver mute lift criteria.
The minimum separation distance required for the
prevention of receiver mute lifts is:
187 NM aircraft against ground offset carrier
systems;
The D/U ratio used will depend on regionally agreed
planning criteria.
Note.- The application of the 14 dB planning
criteria assumes that it is highly unlikely that two
aircraft will be at the maximum edge of their respective
service volumes and at the closest point between these
two volumes.
C) 8.33 kHz channels spaced 25 kHz away from an
assigned frequency of a 25 kHz channel should be
planned in accordance with 2.2.
3. Criteria to be employed in establishing
adjacent channel frequency deployment of
VHF facilities that have a service range
beyond the radio horizon
For the most economical use of frequencies and to ensure
freedom from interference, planning must be based on an
accurate knowledge of equipment used. When the equipment
characteristics and field strength (or attenuation) curves are
on hand for the troposcatter regions, it is relatively easy to
determine the required geographical separation. When these
are not known, the maximum permitted antenna gain
stipulated in 4.1.6.1 will be assumed. There are several
conditions that must be calculated and compared to determine
the appropriate separation to be used. The conditions to
be compared are:
1) ground facility-to-aircraft;
2) aircraft-to-ground facility;
1111101 ATT A-4
Attachment A Annex I0 - Aeronautical Telecommunications
3) aircraft-to-aircraft; and
4) ground facility-to-ground facility.
Case 1.- For the case of protection of aircraft A from a
ground facility (see Figure A-4):
A. Determine the signal level S (dB re]. 1 pV/m) received
from the desired station at the limit of the service radius
at the protection altitude.
B. Assign the desired protection ratio P (dB) required at the
aircraft receiver.
C. Let receiver adjacent channel rejection be represented
by A (dB). Then the level L (dB re]. 1 pV/m) that can
be tolerated at the receiver antenna can be determined
by:
for situations where these$eld strengths will not normally be
exceeded more than 5 per cent of the time. These curves were
established by the Institute for Telecommunicatinns Sciences
and Aeronomy of the Environmental Science Services Administration
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