Sighting Antenna Azimuth; Elevation Offset - iDirect evolution x1 Installation Manual

causes the compass to be deflected to the right of the true heading, while West declination
causes the compass needle to deflect to the left of the true heading. Consequently, add West
declination, and subtract East declination, from the compass reading to obtain the true
heading (Mnemonic: "West is Best, East is Least").
For example, the illustration depicts the 10° West isogonic line passing through Baltimore,
MD. In that location, 10 degrees must be added to the compass indication to obtain the true
heading.

2.3.2 Sighting Antenna Azimuth

When sighting the antenna to determine azimuth, it is important to consider the effect of
large metal objects nearby, which could influence the compass measurement.
Measure from behind the antenna, looking in the direction of the feed horn. Walk around
behind the antenna and watch the compass to determine if the field is uniform or if anomalies
exist.
Use an object in the far background as a target to align the compass. Sight along a line
perpendicular to the plane of the reflector. The back plate of the reflector assembly can
serve as a reference.
Add or subtract the declination in your location to the compass reading. This is the true
heading of the antenna. When aligning the antenna to the value determined by the Look
Angle Calculator, mark the position with a line drawn across the lower section of the azimuth
mount and the pole using an indelible marker.

2.3.3 Elevation Offset

An offset antenna has the virtue of unobstructed antenna aperture, especially beneficial for
VSAT terminals. Reflector optics are modified from a parabola, allowing the feed to be placed
off the mechanical axis. The resulting beam (optical) axis is offset by an angle equal to the
angle between the feed and the mechanical axis. See
A typical 1.8 meter antenna has a 22.6° offset, while a typical 1.2 meter antenna has a 17°
offset. For example, the antenna reflector elevation required to achieve a beam angle of 50°
relative to the horizon is calculated as follows for a 1.8 meter antenna:
°
- 22.6
50
The reflector back plate is perpendicular to the mechanical axis of the antenna. When the
back plate is vertical (90°), the beam elevation is 22.6°. To move the beam axis to the desired
50° elevation angle as in the example above, the antenna back plate is elevated from 90° to
117.4° (90 + 27.4) or, depending on the type of inclinometer used, a reading of 62.6° (90 -
27.4).
Always refer the original equipment manufacturer's (OEM) installation instructions when
installing the antenna and mount. Consult the OEM specifications to determine the offset
angle for the particular antenna being installed.
iDirect Satellite Router Installation and Commissioning Guide
iDX Release 3.3
° °
= 27.4
Figure 3.
Orientation
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