Thales 421 - Set Course SBO Amplitude (Course Width)

LLZ 421
Operation and Maintenance Alignment Procedure LLZ−2F (Dip./Refl.)
ILS 420
5−11Ed. 07.08
SOAC
5.3.6 Set Course SBO Amplitude (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. 5−7). 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 amplitude values.
5.3.7 Set Clearance SBO Amplitude
NOTE: Clearance power should be set as low as possible, to avoid disturbances on the course signal.
a) Set TX1 on aerial.
b) Open dialog ’Transmitter1−Waveform Data#1’, open dialog ’Transmitter2−Waveform Data#1’.
c) Set parameter ’CLR SBO Amplitude’ of both TX to 40 %.
d) Measure DDM at the measurement circle and find the minimum DDM value outside the course area
±10°.......±35° (typically around 25°).
e) Set parameter ’CLR SBO Amplitude’ for a DDM indication of approx. 22 % at this point.
NOTE: Adjust to approx. 18 % for 13 elements dipole/reflector antennas.
f) Measure the DDM from +40° to −40° at the measurement circle. The DDM should rise in linear
fashion from the course line until it exceeds 18 %, then remain more than 18 % up to an azimuth
angle of ±35°.
g) Set TX2 on aerial and repeat d), e) and f) for TX2.
h) Note down amplitude values.
5.3.8 Set and Check Capture Ratio
a) Check that cable W29 (13 and 21 elements) between coupler 9 and X400 (power divider course
13 elements) and coupler 8 and X700 (power divider course 21 elements) necessary for setting
the capture ratio corresponds to the operating frequency.
b) Switch both TX on and set TX1 on aerial.
c) Open dialog ’Transmitter1−Waveform Data#1’, open dialog ’Transmitter2−Waveform Data#1’.
d) Set parameter ’CRS SBO Amplitude’ of TX1 to 0 %.
e) Set parameter ’CLR SBO Amplitude’ of TX1 to 0 %.
NOTE: Check the capture ratio by measuring the relative RF levels of the CSB course and CSB clea-
rance on the course line in the farfield (at least 1000 m). The level difference should be
 16 dB for the 13 element, and  18 dB for the 21 element antenna.