Installation Instructions

Table Of Contents

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Connect the antenna cables A1 and A6 to the ADU outputs labelled A1 and A6 respectively.

Connect all other ADU outputs to dummy load. Use the NM3710 with portable test antenna.

On the the runway establish a point officially marked as the centre line for DDM measure-

ments. Ascertain that the measurement point is not affected by reflected signals degrading the

direct received signals from the antenna pairs. This can be tested by moving the test antenna

a few meters back and fourth while observing the DDM reading. If the value is not changing

significantly then the measurement position is OK.

Take a note of the DDM reading first from antenna pair A1/A6.

Connect pair A2/A5 to ADU outputs A2/A5 and disconnect pair A1/A6, dummyload A1/A6

ADU.

Take a note of the DDM reading.

Carry out this procedure until all antenna pairs DDM readings have been noted.

If any antenna pair measures DDM different from zero, one of the antenna pair feed cable

lengths should be trimmed in order to bring the DDM reading to zero.

If the DDM reading is positive (150 Hz dominance) the antenna cable at the right hand side

(A4...A6) should be trimmed.

The sensitivity of DDM versus electrical phase error of 2° (5° CS) is given in the table below:

The sensitivity of DDM versus electrical phase error can be estimated using the following pro-

cedure:

1. Note the DDM value reported by the operator at the Field Test Set for the antenna pair

under test.

2. a) If the DDM value is positive (150 Hz dominance), insert a male-female (MF) N-adaptor

(-9°) in the antenna left side seen forward toward the Field test set.

b) If the DDM value is negative (90 Hz dominance), insert a male-female (MF) N-adaptor

(-9°) in the antenna right side seen forward toward the Field test set.

3. Note the new DDM value. (This value should have oposite polarity compared to the value

without the adaptor.)

4. Calculate the corresponding phase error (electrical degrees) from the formula

: DDM1 (%) measured in item 1.

: DDM

3 (%) measured in item 3.

(Example values from NM3523B)

ϕ°()

9° DDM

DDM

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