858
14 CFR Ch. I (1–1–19 Edition)
§ 171.311
beam transmissions must not exceed 10
microseconds. The rise time at the
edge of each clearance pulse must be
less than 10 microseconds. Within the
fly-right clearance guidance section,
the fly-right clearance guidance signal
shall exceed scanning beam antenna
sidelobes and other guidance and OCI
signals by at least 5 dB; within the fly-
left clearance guidance sector, the fly
left clearance guidance signal shall ex-
ceed scanning beam antenna sidelobes
and all other guidance and OCI signals
by at least 5 dB; within the propor-
tional guidance sector, the clearance
guidance signals shall be at least 5dB
below the proportional guidance signal.
Optionally, clearance guidance may be
provided by scanning throughout the
approach guidance sector. For angles
outside the approach azimuth propor-
tional coverage limits as set in Basic
Data Word One (Basic Data Word 5 for
back azimuth), proper decode and dis-
play of clearance guidance must occur
to the limits of the guidance region.
Where used, clearance pulses shall be
transmitted adjacent to the scanning
beam signals at the edges of propor-
tional coverage as shown in Figure 8.
The proportional coverage boundary
shall be established at one beamwidth
inside the scan start/stop angles, such
that the transition between scanning
beam and clearance signals occurs out-
side the proportional coverage sector.
When clearance pulses are provided in
conjunction with a narrow beamwidth
(e.g., one degree) scanning antenna, the
scanning beam antenna shall radiate
for 15 microseconds while stationary at
the scan start/stop angles.
(3)
Data function format.
Basic data
words provide equipment characteris-
tics and certain siting information.
Basic data words must be transmitted
from an antenna located at the ap-
proach azimuth or back azimuth site
which provides coverage throughout
the appropriate sector. Data function
timing must be in accordance with
Table 7a.
T
ABLE
6—A
NGLE
S
CAN
T
IMING
C
ONSTANTS
Function
Max
value of
t
(usec)
T
o
(usec)
V(deg/
usec)
T
m
(usec)
Pause
time
(usec)
T
t
(usec)
Approach azimuth .....................................................................
13,000
6,800
0.02
7,972
600
13,128
High rate approach azimuth ......................................................
9,000
4,800
0.02
5,972
600
9,128
Approach elevation ...................................................................
3,500
3,350
0.02
2,518
400
N/A
Back azimuth .............................................................................
9,000
4,800
¥
0.02 5,972 600 9,128
T
ABLE
7a—B
ASIC
D
ATA
F
UNCTION
T
IMING
Event
Event time slot
begins at:
1
15.625
kHz clock
pulse
(number)
Time
(milli-
sec-
onds)
Preamble ...............................................
0 0
Data transmission (bits I
13
–I
30
) ..............
25 1
.600
Parity transmission (bits I
31
–I
32
) ............
43 2
.752
End function (airborne) ..........................
45
2 .880
End guard time: end function (ground)
................
3 .100
1
The previous event time slot ends at this time.
T
ABLE
7b—A
UXILIARY
D
ATA
F
UNCTION
T
IMING
—
(D
IGITAL
)
Event
Event time slot
begins at:
15.625
kHz clock
pulse
(number)
Time
(milli-
sec-
onds)
Preamble ...............................................
0 0
Address transmission (bits I
13
–I
20
) ........
25 1
.600
Data transmission: (bits I
21
–I
69
) .............
33 2
.112
T
ABLE
7b—A
UXILIARY
D
ATA
F
UNCTION
T
IMING
—
(D
IGITAL
)—Continued
Event
Event time slot
begins at:
15.625
kHz clock
pulse
(number)
Time
(milli-
sec-
onds)
Parity transmission (bits I
70
–I
76
) ............
82 5
.248
End function (airborne) ..........................
89
5 .696
End guard time; end function (ground)
................
5 .900
T
ABLE
7c—A
UXILIARY
D
ATA
F
UNCTION
T
IMING
—
(A
LPHANUMERIC
)
Event
Event time slot
begins at:
15.615
kHz clock
pulse
(number)
Time
(milli-
sec-
onds)
Preamble ...............................................
0 0
Address transmission (bits I
13
–I
20
) ........
25 1
.600
Data transmission: (bits I
21
–I
76
..............
33 2
.112
End function (airborne) ..........................
89
5 .696
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