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Appendix C: Miscellaneous
C-2
Performance optimization for blockage
Minimum elevation angle
One safe way of getting optimum performance under the current conditions is to switch to
a satellite in view as fast as possible. This is done by having well defined satellite parameters
in the VSAT modem configuration. It is the VSAT modem that has the task of selecting the
correct satellite, and since the VSAT modem is only concerned about the satellite visibility
at the current geographic position, it is very important to enter the minimum elevation of a
satellite at which a stable link can be established.
It is often seen that the minimum elevation is set to 0 (zero). A setting of 0 is not only in
many cases below the usable limit of the satellite, but also a violation against ETSI EN 302
340, where a calculated minimum elevation ranges from 12° to 3° depending on power and
bandwidth must be ensured or FCC §25.205 which states the minimum elevation to be 5°.
Unless the vessel is operating in international waters with no other options, a minimum
elevation of 10° or higher is recommended.
Conclusion
Fewer but well-functioning satellites to choose from give better user performance than
having many satellites, which may have a longer uptime but do not provide a stable data
connection. In the end it is not the actual uptime the subscriber is concerned about, but it is
the uptime where the link gives a stable data connection.
