On Mon, 12 Jan 2004 17:52:40 GMT, Terry Spragg
wrote:

How much accuracy do you need? To resolve satellite
pointing issues, a fixed 3 axis setup (six sensors) will be
required, with integration of the outputs to derive azimuth and
elevation, unless you servo the yaw efficiently and then sense
the elevation, then you only need juggle two indications. You
might use an electronic compass to control the yaw of the antenna
platform. Daily adjustments of magnetic variation might be needed
in passage, and as well, you would need to integrate compass
variations due to local ferrous masses at various headings.
Perhaps a gyrocompass?

The (Inmarsat D+) satellite transceiver uses an omnidirectional antenna, so
no moving parts. According to the specs it has an elevation mask angle of 5°
so one can theoretically work out where in the world it will have coverage of
the Inmarsat satellites. However, the certifying body wants practical tests
done in real-life conditions before certifying it for marine use. We aren't
the manufacturer, only end-users, but need certification for our work.

The units may work up to the theoretical limits in perfect weather, but the
aim is to see how much degradation of performance there is in bad weather -
when the units would be more likely used.

Dave