NORMARC NM 7000 Series, Installation & Commissioning Handbook

Page: 106 / 189

6 NM 3543 Null reference antenna system adjustments - Glide path
6.1 Mechanical alignment of mast and antennas
6.1.1 Preparation of mechanical- and electrical data
A ground level plot made with theodolite should be available. From this plot Forward slope
(FSL) and Sideway slope (SSL) can be calculated. FSL is defined negative for falling forward
slope seen from the GP mast. SSL is defined positive for rising side slope seen from the GP
mast toward the runway.
In order to calculate the data needed to position the GP mast, the antenna elements and near
field antenna, the following parameters must be known:
•
Forward slope (FSL)
• Sideway slope (SSL)
• Sideway distance from runway centreline to GP mast
• Operating glide path angle
• GP rf channel frequency
The mechanical data outputs are:
•
Antenna forward shift, same as FSL
• Antenna elements heights
• Antenna elements offsets
• Near field monitor antenna distance and height
• Threshold data
6.1.2 Forward shift (FWD)
The antennas should be vertically offset to compensate for forward slope (FSL). See Section
1, Chapter 3.6.3.
6.1.3 Antenna heights
Antenna heights shall be referenced to the intercept point of the terrain slope and the GP
mast. In addition rf wave penetration a few centimetres into the soil (reflection plane) shall be
included to equal the specified antenna heights. See Section 1, Chapter 3.6.3.
6.1.4 Antenna offsets.
The antenna offsets derived from (51.0) shall be accurately adjusted such that the upper ele-
ment is closer to the runway than the lower element. See Section 1, Chapter 3.6.3.
6.2 Electrical measurements
6.2.1 Antenna cable lengths (Electrical phase equality)
Each antenna cable must be electrically measured before the end connector is terminated in
the Antenna.
Utilise a vector voltmeter or network analyser. Establish the lower antenna cable (A1) return
phase as 0° reference phase.