Mark Wolfe wrote:
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At sea systems get into $$$$, you have to track the satellite.
No you don't. The antenna is omni directional. Our systems are curently
used in boat races, to remotely monitor cargo holds (mostly
refrigerated), in aircraft, on trucks, Volvo uses them in their trucks
here in the US and in Brazil.
Boats
tend to pitch, roll and yaw. So, in order to compensate for this, and
keep your antenna locked on a bird, you need to detect movement of the
ship. Most the commercial stuff I've worked with has had a small
roll/pitch gyro in it, and took heading from the ships compass.
GPS also provides heading and speed. It can provide altitude as well,
but the resolution is only +/- 20 meters.
They
fed all this to a computer which then positioned the antenna. These
systems run the cost of a nice car, but you get TV at sea. Inmarsat is
the same.
Inmarsat D+ is omni directional. The whole unit is about 4" diameter,
but it's not broadband by any stretch.
With our systems we'd get 64kbit and it would run around 8
bucks a minute. Not sure with the new iridium stuff, but I still
imagine it will be expensive.
Our initial Iridium product will not be expensive. It will be lower
bandwidth (205 bytes max. message size). Again, it's omni directional.
Again, still got to compensate for ships
movement. You won't see them on small craft, as it's too cost
prohibitive. For good signal strength, you'd need about a 1 meter dish,
then you'd need to protect it with a radome. These things take up room,
and there's not much above deck space on a sub 40 foot boat for one.
Again, you do not need a dish. They are all omni directional and of
significant power. Antennas typically have 3dB gain, some have more. Our
modems receive at -120dBm - very sensitive. Current modems run from $100
- $800, depending upon model and quantity. Transmit power is 6W ORBCOMM,
~4W Inmarsat D+, .3W cellular, with the Iridium unit at 2W.
PGA
--
Paul G. Allen
Owner, Sr. Engineer, Security Specialist
Random Logic/Dream Park
www.randomlogic.com
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