NORMARC NM 7000 Series, Installation & Commissioning Handbook

Page: 71 / 189

1.3.1 DDM check of ADU O/P (output port)
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.
For each course sector width (CS) of the array a set of corresponding DDM values exists
unique for each antenna O/P.
For CS = 5°:
For other CS values use the formula:
Example
A3 DDM for CS = 5.4°:
PROCEDURE
Insert the 90°-stub into the SBO path.
Connect a directional coupler with 50* load to antenna O/P A3.
Connect the NM3710 (use 20 dB attenuator at NM3710 I/P) to the directional coupler's for-
ward port.
Adjust the SBO attenuator (for the Tx to air) until the DDM value equals the previously calcu-
lated value for the CS.
%DDM µA %SDM
A2 -34.8 -337 40.0
A3 -32.7 -316 40.0
DDM
2 SBO
⋅
CSB
-------------------COS
γ
=
DDM
A n
( )
DDM
5
° ( )
5
° ⋅
CS
---------------------------------
=
DDM
A3
32.7 5
⋅
–
5.4
--------------------- 29.5% = =