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Navigation

You could say that Ephemeris data enables the GPS receiver to calculate position,

while almanac data helps the GPS receiver know where to look for other

satellites.

If you start a GPS that has not been started recently or has been moved and does

not know its position, it takes about 12.5 minutes to transfer almanac data and

easily 15 minutes before you have a 3D position.

The Control Segment

The Control Segment is located in the USA. It sends information to each satellite

via Ground Antennas. This information, as well as information from the satellite's

atomic clock, is transmitted in the form of two sideband signals at 1575.42 MHz

and 1227 MHz.

Using this information, a GPS receiver can calculate the aircraft's position.

The User Segment

The User Segment consists of the

receivers we have in our

airplanes. They can have

different numbers of channels.

Often 5, 8 or more and often they

can receive both GPS and
Glonass satellites.

In order to function optimally, you need signals from at least 4 satellites to get
3D navigation.

They must be able to deliver accurate data to the user at least 95% of the time.

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