3.3.1
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.
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 = 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.
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.
Move the directional coupler to A4, A5 and compare readings with calculated values. If mea-
sured DDM is lower than the calculated values for A4, A5 then increase the SBO power, or
vice versa, until a fairly good matching set of values are obtained.
% DDM
µA
%SDM
A3
-40.0
-387
53.8
A4
-38.3
-371
40.0
A5
-22.9
-222
40.0
DDM
A n
( )
DDM
4
°
( )
4
°
⋅
CS
---------------------------------
=
DDM
A3
53.8 4
⋅
–
5
---------------------
43.0%
=
=
Summary of Contents for NM 7000 Series
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