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of the United States.
Note 2.- For power levels other than I kW the necessary
corrections under "C" would have to be made. For example,
5 kW ERP requires a minus 7 dB correction.
E. The facility-to-facility separation D is d (km) plus
service radius (km).
Case 2.- Aircraft (A)-to-ground facility (see Figure A-4):
A. Determine signal level Sg at the ground facility
receiving antenna for proper system operation.
B. Proceed as in Case 1, where
D. Distance d (km) from protection point to undesired
facility to provide protection established by "C", is
found by application of L to the appropriate curves.
Note 1.- Figures A-8 to A-15 are field strength curves
appropriate for the average temperate climate over land or
sea, which may be used to determine geographical separation
C. Ground facility-to-ground facility separation will also be
determined as in Case 1 (D = d + service radius (km)).
Note.- Where ground facility receivers have sensitivities of
less than 1 microvolt across 50 ohms, Case 2 is most likely to
yield the separation to be used.
Figure A-4. Air-to-ground (facility from A)
and ground-to-air (A from facility)
ATT A-5
Annex I0 - Aeronautical Telecommunications Volume V
Figure A-5. Facility-to-facility separation based on air-to-air
(A from B) and ground-to-ground (C and D)
Aircraft
Wanted Unwanted
t r a n s m / ~ i \ transmitter
100 watts ERP 100 watts ERP
Radio horizon Radio horizon
Figure A-6. VOLMET planning
(illustrating co-channel protection)
Aircraft
?
I
I
I
I
Wanted Unwanted
transmitter transmitter
Figure A-7. VOLMET planning (illustrating adjacent
channel protection)
ATT A-6
Attachment A Annex 10 - Aeronautical Telecommunications
Case 3.- Aircraft (A)-to-aircraft (B) (see Figure A-5):
A. Establish service radius and protection altitude for
facility to be protected (see aircraft A in Figure A-5).
B. Determine closest point to aircraft A that aircraft B will
be transmitting to the ground facility site and the altitude
where this will take place.
C. Proceed as in Case 1, using the aircraft (B) contacting
ground facilities as the undesired signal.
E. The distance d to aircraft B (undesired) obtained from
the curves, plus the service radius of the facility to be
protected, will determine the separation between aircraft
B and the ground facility protected.
F. Facility-to-facility separation may then be determined
graphically or by trigonometric means.
Case 4.- Ground facility-to-ground facility (see
Figure A-5).
A. Determine signal level that can be tolerated at the
receiver antenna at one facility by L = Sg - P + A (see
Case 1).
B. Then facility-to-facility separation for these conditions
is read directly from the curves (after correcting for
transmitter power of other facilities if different from
1 kW).
C. Should equipment at the two facilities have different
characteristics, repeat procedure in "A" and "B for the
other combinations of equipment.
D. Of the two distances derived, use the greater to compare
with other cases (see below).
Note.- In most instances, it will be found that the
facility-tofacility consideration will not be the controlling
factor in determining geographical separation
Facility separation will then be the greatest distance derived
for Cases 1 to 4.
4. Criteria to be employed in
establishing geographical separation
between ground stations and between
aircraft and ground stations for co-channel
operation of VHF facilities that have a service
area beyond the radio horizon
Geographical separation of co-channel facilities can be
calculated by using the method given in 2 above except that
the adjacent channel rejection A is omitted from
consideration.
5. Criteria employed in establishing
co-channel frequency deployment of
VHF VOLMET facilities
In the case of VHF VOLMET services, the geographical
separation between co-channel stations should be 55.6 km
(30 NM) plus twice the distance to the radio horizon from an
aircraft at the highest altitude flown by aircraft in the area
concerned. (See Figure A-6.)
Note.- At 27.8 km (15 NM) beyond the radio horizon, the
field strength at 13 500 m (45 000 fi), from a transmitter of
100 W ERe will be approximately at the receiver muting level
of 5 microvolts per metre.
6. Criteria employed in establishing
adjacent channel frequency deployment
of VHF VOLMET facilities
6.1 For aircraft receivers designed for operation in a
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