Thales 421, Эксплуатация и обслуживание, Страница: 100 / 256

LLZ 421
Alignment Procedure LLZ−1F (Dip./Refl.) Operation and Maintenance
ILS 420
4−10
Ed. 01.10 SOAC
4.3.4 Course Width
a) Switch both TX on and set TX1 on aerial.
b) Open dialog ’Transmitter1−Waveform Data#1’, open dialog ’Transmitter2−Waveform Data#1’.
c) Set parameter ’CRS CSB RF−Level’ of both TX to 25 W.
d) Set parameter ’CRS SBO Amplitude’ of both TX to 40 %.
e) Measure DDM with the portable DDM instrument at the width points of the threshold at a distance
of 107 m to the left or right (test point B or C, Fig. 4−6). Then set CRS SBO Amplitude so that DDM
is −15.5 % on left (150 Hz predominant), as seen from DDM measurement point or +15.5 % on
right (90 Hz predominant), as seen from DDM measurement point.
NOTE: Sign + or − depends on measurement equipment used.
f) Set TX2 on aerial.
g) Set parameter ’CRS SBO Amplitude’ of TX2 for DDM 15.5 % at the width points, as well.
h) Note down the amplitude values.
4.3.5 Measure Course Position at the Threshold
Measure DDM with the portable DDM instrument at the threshold along the nominal course line at
at least 3 different points at a distance of approx. 10 m, and form the mean value. The mean value
should not deviate from the nominal course line by more than ±2m. If not repeat the null setting for
the course antenna. To perform this procedure refer to the appropriate Part 3 of the LLZ−manuals:
Antenna System Description for Dipole Reflector Antenna System.
4.3.6 Performing Ground Check on Measurement Circle
Perform a ground check on the measurement circle (see Fig. 4−6 (D) and Fig. 4−7) for each transmit-
ter. Measure the DDM and SDM on each ground check point (−35°, −30°,
…
, 0°,
…
, +30°, +35°)
and draw a diagram with these values. As example, a typical diagram resulting from measurement
with a 14 element antenna is shown in Fig. 4−1.
NOTE: The DDM should rise in linear fashion from the course line until it exceeds 18 %, then remain
greater than 18 % up to an azimuth angle of ±35°.
50 %
40 %
30 %
20 %
10 %
0%
−10 %
−20 %
−30 %
−40 %
−50 %
−60° −40° −20° 20° 40° 60°
Localizer (antenna 14 elements
DDM
SDM
40 %
38 %
37 %
35 %
33 %
NOTE: Typical DDM and SDM values. Result of measurement depends on runway length and threshold distance
150 Hz predominant
90 Hz predominant
linear range (±15.5 %)
DDM
SDM
Runway
0°
TX1
TX2
Fig. 4−1 Example diagram for ground check on measurement circle (here 1F, 14 element)