98-175666-C
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.
