Forum Archive Index - April 2004

["david.gibson" <david.gibson@k.co.nz>]

Concerning your question about VSAT:

>MY Question:
"How does the V-SAT fit into it? And also ViaSat. Your news 19th May 2003
speaks of deployment of its V-SAT technology into 10 commercial sites.  Is
V-SAT the terminal gear that communications with the satelite?  The article
also says ViaSat is on eof Amercia's largest V-SAT organisations."

>MUL Answer:
"VSAT stands for very small aperture technology - spot beam - and is the 2
way technology we deploy and buy from ViaSat in the US. You are correct in
that this is the equipment at each of our customers sites which now number
far more than the original 10 we spoke of last year. Sites are now located
in Australia, PNG,Timor, Iraq, Afganistan, Kuwait and Bahrain."


My understanding of VSAT is that it is a property of the terminal device as
a consequence of the higher frequency used in the transponder.

[Physics ON]

The frequency of a signal is inversely proportional to its wave length.  The
higher the frequency - the shorter the wavelength.

To be efficient, an antennae needs to be of the order or longer than the
wavelength of the signal it is detecting/transmitting.  Hence for the early
C and Ku band devices - this was measured in meters.  Modern L band
transponders broadcast in cm's.

The power required to transmit a signal a certain distance with a defined
intensity is related to the frequency to the fourth power!  The higher the
frequency - massively more power is required to transmit the signal.  On
satellites - the power budget is very constrained (solar cells and
batteries).  Improving technology (more power efficiency from the power
system - less draw from the onboard electronics) has allowed increasing
power budgets for transponders.  Hence, higher frequencies can be deployed.
Hence smaller aperature antennae can be used on the ground. (VSAT)

[Physcis OFF]

VSAT has nothing to do with the beam geometry.  VSAT technology is now
deployable on trucks, aircraft, etc ...  VSAT telephones are used by the
military.

Best Rgds
/dbg


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