5.3
Course sector width adjustment
The required course sector width (CS) can be pre-adjusted by two methods:
1. DDM measurement of ADU antenna feed outputs.
2. DDM field check.
Preferably both methods should be carried out and compared.
5.3.1
DDM check of ADU O/P
At each antenna feed output of the ADU the measured DDM is a result of the SBO/CSB ratio
according to the formula
where
CSB is a fixed value.
SBO is adjustable by the SBO attenuator in the cabinet.
γ
is 0° when the 90°-stub is inserted into the SBO and clearance transmitter is switched off.
For each course sector width (CS) of the array a set of corresponding DDM values exists
unique for each antenna O/P.
For CS = 4°:
For other CS values use the formula:
Example
A3 DDM for CS = 3.5°:
PROCEDURE
Turn off the clearance transmitter. Insert the 90°-stub into the course SBO path.
Connect a directional coupler with 50
Ω
load to antenna O/P A3.
% DDM
µ
A
% SDM
A3
-33.7
-326
40.0
A4
-24.9
-241
40.0
A5
-17.9
-173
40.0
DDM
2 SBO
⋅
CSB
-------------------COS
γ
=
DDM
A n
( )
DDM
4
°
( )
4
°
⋅
CS
---------------------------------
=
DM
A3
(
)
33.7 4
⋅
–
3.5
---------------------
38.5%
=
=
Summary of Contents for NM 7000 Series
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