*
General GPS data reports
*
Fault information reports.
The left and right MMRs also send position data to the ground proximity warning computer (GPWC). The GPWC uses this data in its terrain awareness and terrain clearance floor functions.
Time Mark
The left and right MMRs supply time mark pulses to each AIMS cabinet. The pulses occur once per second and have an amplitude of approximately four volts. These pulses are the same as accurate universal time (coordinated) (UTC).
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GPS -GPS ANTENNA
General
The GPS antennas receive L-band frequency signals and send them to the multi-mode receivers (MMRs).
The GPS antenna impedance is 50 ohms.
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GPS -THEORY OF OPERATION -1
GPS Segments
The GPS has three segments:
*
Satellite
*
User
*
Control.
Satellite Segment
The satellite segment is a group of satellites that orbit approximately 10,900 nautical miles above the earth. Each satellite completes an orbit approximately once every 12 hours. There are 21 operational satellites and 3 spares.
The satellites continuously transmit radio signals with navigation data, range code, and the exact time.
User Segment
The user segment is the multi-mode receiver (MMR) on the airplane. It receives the satellite signals. The MMR uses the satellite data to calculate the airplane position.
Control Segment
The control segment has control and monitor stations on earth that continuously monitor and track the satellites. The purpose of the control segment is to:
* Monitor and correct satellite orbits and clocks
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Calculate and format a satellite navigation message. This message has up-to-date descriptions of the satellites future positions, and a collection of the latest data on all GPS satellites
*
Update the satellite navigation message regularly.
The control segment has one master control station and five monitor stations. Three of the monitor stations are also upload stations.
The master control station is in Colorado Springs, Colorado USA. The master control station is the operational center of the GPS. The master control station controls all operations in the control segment. The master control station has an atomic clock. This clock is the reference for the GPS.
The monitor stations track the satellites 24 hours a day. The master control station remotely controls the monitor stations through on-line connections. The monitor stations are in these locations:
*
Ascension island
*
Colorado Springs, Colorado USA
*
Diego Garcia island
*
Hawaii
*
Kawajalein island.
The monitor stations receive the same information from the satellites that the MMRs in the airplane receive. The monitor stations:
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GPS -THEORY OF OPERATION -1
*
Record the accuracy of the satellite clocks
*
Collect and relay to the control station meteorologic data such as barometric pressure, temperature, and dew point. The master control station uses this data to calculate the tropospheric signal delay
*
Continuously measure the ranges to all visible satellites. The master control station uses this data to calculate and predict the satellites orbits.
The master control station uses the upload stations to send:
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