Sea Tel 9797B-70 C-Band TX/RX, Installation And Operation Manual

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Basic System Information 9797B-70 C-Band TXRX
3-2
Figure 3-1 Satellite Signal Polarization
3.1.5. Satellite Footprints
The focused beam(s) from the satellites are normally aimed at the major land masses where there are large
population centers. Footprint charts graphically display the signal level expected to be received in different
geographic locations within the area of coverage. The signal will always be strongest in the center of the
coverage area and weaker out toward the outer edges of the pattern. The coverage areas are intended to be
a guide to reception, however, the actual coverage area and signal level and vary. Also the signal strength is
affected by weather.
3.1.6. Linear Satellite polarization
Satellites may transmit their signals in
one of two different polarization
modes. The feed installed on your
antenna must be designed to operate
with linear polarized satellite
transmissions.
Circular polarized satellite
transmissions do not require
polarization adjustment to optimize
the reception.
Linear polarized satellite transmissions
require periodic adjustment of
“polarization” to optimize the
alignment of the LNB to the angle of the signal from the satellite.
When you are at the same longitude as the satellite, its’ horizontal and vertical signals will be aligned to your
local horizon. When you are east or west of the satellite, the signals will appear to be rotated clockwise or
counter-clockwise from your local horizontal and vertical. Both horizontal and vertical signals from a satellite
will appear to be rotated the same amount and are always perpendicular to each other. The amount of
rotation is dependent on how far east or west you are form the satellite and how close you are to the
Equator.
3.2. Antenna Basics
The following information is provided to explain some of the basic functions of the antenna:
3.2.1. Unlimited Azimuth
Azimuth rotation of the antenna is unlimited (no mechanical stops). Azimuth drive, provided by the azimuth
motor, is required during stabilization, searching and tracking operations of the antenna. When the ship turns,
azimuth is driven in the opposite direction to remain pointed at the satellite. The actual azimuth pointing
angle to the satellite is determined by your latitude & longitude and the longitude of the satellite. It is
important to know that the antenna should be pointed (generally) toward the equator.
The azimuth angle to the satellite would be 180 degrees true (relative to true north) if the satellite is on the
same longitude that you are on. If the satellite is east, or west, of your longitude the azimuth will be less than,
or greater than 180 degrees respectively.
When checking for blockage you can visually look over the antenna radome toward the equator to see if any
objects are in that sighted area. If you are not able to find any satellites it may also be useful to remove the
radome hatch to visually see if the dish is aimed the correct direction (towards the equator).
3.2.2. Elevation
In normal operation the elevation of the antenna will be between 00.0 (horizon) and 90.0 (zenith). The
antenna can physically be rotated in elevation below horizon and beyond zenith to allow for ship motion.
Elevation drive, provided by the elevation motor, is required during stabilization, searching and tracking
operations of the antenna. The actual elevation pointing angle to the satellite is determined by your latitude
& longitude and the longitude of the satellite. In general terms the elevation angle will be low when you are
at a high latitudes and will increase as you get closer to the equator.
Additionally, from any given latitude, the elevation will be highest when the satellite is at the same longitude
that you are on. If the satellite is east, or west, of your longitude the elevation angle will be lower.