Thales 421, Эксплуатация и обслуживание, Страница: 126 / 256

LLZ 421
Alignment Procedure LLZ−2F (Dip./Refl.) Operation and Maintenance
ILS 420
5−12
Ed. 07.08 SOAC
f) Set parameter ’CLR CSB RF−Level’ of TX1 to 0 W.
g) Measure the RF level of the CRS transmitter only.
h) Set parameter ’CRS CSB RF−Level’ of TX1 to 0 W.
i) Set parameter ’CLR CSB RF−Level’ of TX1 to 25 W.
j) Measure the RF level of the CLR transmitter only.
The difference ( RF Level
course only
− RF Level
clearance only
) between the two results in g) and j)
should be 18 dB. If necessary, the optimum value of the operating frequency can be determined
by extending the cable length between coupler 9 and X400 (power divider course,13 elements)
and coupler 8 and X700 (power divider course, 21 elements). The cable length is optimized for the
highest frequency 112 MHz. If necessary,it may be set to the desired length by inserting phase
adapters. Initial informative measurements can also be taken using the optional nearfield course
dipole, though the level differences which are obtained will be less than in the farfield due to near-
field disturbances in the course system.
k) Set parameter ’CRS CSB RF−Level’ of TX1 to 25 W.
l) Set parameters ’CRS SBO Amplitude’ and ’CLR SBO Amplitude’ to noted down values as deter-
mined in Section 5.3.6 and 5.3.7.
5.3.9 Measure Course Position at 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.
5.3.10 Performing Ground Check on Measurement Circle
Perform a ground check on the measurement circle (see Fig. 5−8) for each transmitter. 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 21 element an-
tenna is shown in Fig. 5−1.
50 %
40 %
30 %
20 %
10 %
0%
−10 %
−20 %
−30 %
−40 %
−50 %
−60° −40° −20° 0° 20° 40° 60°
Localizer (antenna 21 elements)
DDM
SDM
45 %
43 %
41 %
39 %
37 %
35 %
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 %)
CLR Width point
CLR Width point
DDM
SDM
Runway
Fig. 5−1 Example diagram for ground check on measurement circle (21 element)