Theoretically, DDM should be close to -0.9% DDM (90) as a minimum value due to path loss
differences between antennas seen from the NF antenna.
7.6.1
Near Field Monitor Position Search
A de-phasing test procedure of upper antenna (A2) can be carried out in order to search for
the optimum monitor position.
An "elbow" type N-adapter (-21°) is inserted in the lower antenna feed (A1). This is equivalent
to advance (+) phase of the upper antenna.
Retard (-) phase is introduced by inserting the "elbow" adapter in A2 only.
The DDM readings and correlation of the monitor antenna signal to the CL integral from MCU
(far field) should theoretically be:
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In order to look for the optimal distance between the GP mast and the NF antenna carry out
the following test:
Measure DDM at pos1 m and -1 m of original position. Then compare the results with
the theoretical values for these offsets from the nominal 180° position, as denoted below:
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Based on the comparing results then determine the best correlated position for the NF monitor
antenna.
Dephasing
Near Field (NF)
Far field (CL)
21° retard
-13µA/-1.5% DDM
-11µA/-1.3% DDM
21° advance
-11µA/-1.3% DDM
-13µA/-1.5% DDM
Dephasing
NF 1 m forward
NF 1 m backward
21° retard
-19µA/-2.2% DDM
-9µA/-1.1% DDM
21° advance
-7µA/-0.8% DDM
-16µA/-1.9% DDM
Summary of Contents for NM 7000 Series
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