Thales 421, Operation And Maintenance, Page: 99 / 256

LLZ 421
Operation and Maintenance Alignment Procedure LLZ−1F (Dip./Refl.)
ILS 420
4−9
Ed. 01.10 SOAC
4.3 SETTING OF TRANSMITTER AND ANTENNA
4.3.1 Adjusting CRS CSB Signal
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 CSB SDM’ of both TX to 40 %.
e) Set parameter ’CRS CSB DDM’ of both TX to 0 %.
f) Set parameter ’CRS SBO Amplitude’ of both TX to 0 %.
g) Measure SDM and DDM of CSB course signal for TX1 with the portable DDM instrument in the
radiation field at the measurement circle (close to the course line) or use RF signal from nearfield
dipole and connect it to portable instrument. If necessary, correct SDM and DDM of TX1 to get an
indication of 40.0 % SDM and 0.0 % DDM.
h) Open dialog ’Transmitter1−Waveform Data#1’, open dialog ’Transmitter2−Waveform Data#1’.
Set parameter ’Ident AM’ for both TX e.g. to 10 %
.
Use portable instrument. Check if IDENT is mea-
sured by execut. monitors.
i) Set TX2 on aerial. Perform the same procedure as for TX1 in step g) and h).
j) Switch both TX off.
4.3.2 Set CSB/SBO Phase
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 portable DDM instrument at a distance of approx. 1000 m (test point A or A’,
Fig. 4−6) and at approx. 2° away from course line; then set CRS SBO Phase so that the instrument
indicates DDM 0 (Phase in Quadrature).
NOTE: Range of values 0...359°
f) Read out phase value determined in e). Then add or subtract 90° to or from it and enter as new
value, so that150 Hz predominates to the left of the course line, as seen in the radiation direction.
If not, a further 180° must be either added or subtracted (Normal Phase).
g) Set TX2 on aerial and repeat the phasing for TX2 with steps b) to f).
h) Switch both TX off.
4.3.3 Check SBO null of Course Antenna
The DDM null must not deviate from the nominal course line by more than ±10 cm at a distance of
300 m from the LLZ antenna, and the DDM must rise in a linear fashion from the null on either side.
If not, the dipoles must be phased as follows in pairs. To perform this procedure refer to the appropri-
ate Part 3 of the LLZ−manuals: Antenna System Description for Dipole/Reflector, Chapter 4.