NORMARC NM 7000 Series, Installation & Commissioning Handbook

Page: 95 / 189

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 = 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.
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.
Adjust the SBO attenuator for the other Tx to the same setting.
Remove the 90°-stub.
A3 -33.0% DDM
A4 -29.3% DDM
A5 -26.0% DDM
DDM
2 SBO
⋅
CSB
-------------------COS
γ
=
DDM
A n
( )
DDM
4
° ( )
4
° ⋅
CS
---------------------------------
=
DDM
A3
33.0 4
⋅
–
3.5
---------------------
37% – = =