Sea Tel ST88-21 C/Ku-Band TVRO, Installation And Operation Manual

Page: 15 / 145

ST88-21 C/Ku-Band TVRO Site Survey
2-1
2. Site Survey
There are three objective of the site survey. The first is to find the best place to mount the antenna and the BDE. The second is
to identify the length and routing of the cables and any other items or materials that are required to install the system. The third
is to identify any other issues that must be resolved before or during the installation.
2.1. Site Selection Aboard The Ship
The radome assembly should be installed at a location aboard ship where:
•
The antenna has a clear line-of-sight to view as much of the sky (horizon to zenith at all bearings) as is
practical.
•
X-Band (3cm) Navigational Radars:
•
The ADE should be mounted more than 0.6 meters/2 feet from 2kW (24 km) radars
•
The ADE should be mounted more than 2 meters/8 feet from 10kW (72 km) radars
•
The ADE should be mounted more than 4 meters/12 feet from 160kW (250km) radars
•
S-Band (10cm) Navigational Radars:
•
If the ADE is/has C-Band it should be mounted more than 4 meters/12 feet from the S-band Radar.
•
The ADE should not be mounted on the same plane as the ship's radar, so that it is not directly in the radar
beam path.
•
The ADE should be mounted more than 2.5 meters/8 feet from any high power MF/HF antennas (<400W).
•
The ADE should be mounted more than 4 meters/12 feet from any high power MF/HF antennas (1000W).
•
The ADE should also be mounted more than 4 meters/12 feet from any short range (VHF/UHF) antennae.
•
The ADE should be mounted more than 2.5 meters/8 feet away from any L-band satellite antenna.
•
The ADE should be mounted more than 3 meters/10 feet away from any magnetic compass installations.
•
The ADE should be mounted more than 2.5 meters/8 feet away from any GPS receiver antennae.
•
Another consideration for any satellite antenna mounting is multi-path signals (reflection of the satellite
signal off of nearby surfaces arriving out of phase with the direct signal from the satellite) to the antenna.
This is particularly a problem for the onboard GPS, and/or the GPS based satellite compass.
•
The ADE and the BDE should be positioned as close to one another as possible. This is necessary to reduce
the losses associated with long cable runs.
•
This mounting platform must also be robust enough to withstand the forces exerted by full rated wind load
on the radome.
•
The mounting location is robust enough that it will not flex or sway in ships motion and be sufficiently well
re-enforced to prevent flex and vibration forces from being exerted on the antenna and radome.
•
If the radome is to be mounted on a raised pedestal, it
MUST
have adequate size, wall thickness and gussets
to prevent flexing or swaying in ships motion. In simple terms it must be robust.
If these conditions cannot be entirely satisfied, the site selection will inevitably be a “best” compromise between the
various considerations.
2.2. Antenna Shadowing (Blockage) and RF Interference
At the transmission frequencies of C and Ku band satellite antenna systems, any substantial structures in the way of
the beam path will cause significant degradation of the signal. Care should be taken to locate the ADE so that it has
direct line-of-sight with the satellite without any structures in the beam path through the full 360 degree ships turn.
Wire rope stays, lifelines, small diameter handrails and other accessories may pass through the beam path in limited
numbers; however, even these relatively insignificant shadows can produce measurable signal loss at these
frequencies.