航空电子设备 无线电高度表
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Consequently, during the time interval △T, the transmitter frequency has changed from f1 to f2. The frequency difference for given altitude is equal to △F(=f2-f1 ) which is proportionate to △T.
NBAA 2003
1
Radio Altimeter ( RA)
NBAA 2003
Radio Altimeter
无线电高度表
Civil Aviation Flight University of China 2
Radio Altimeter ( RA)
NBAA 2003
The radio altimeter system provides accurate terrain clearance altitude information displayed in the flight compartment, for use by the flight crew.
The rate of frequency modulation is 100 times per second. The radio altitude is computed by determining the difference between the frequency of the reflected signal and the frequency of the signal being transmitted at the instant the reflected signal is received.
The radio altimeter is called ‘low range’ because it is not intended to operate at airplane altitudes above ground greater than 2500 feet. Its principal usage is during the final approach and takeoff. By the abbreviation LRRA, we mean “Low Range Radio Altimeter”.
If at time t1, frequency f1 is transmitted to the ground, the same frequency f1 will be received, after reflection, at time t2.
The time difference △T= t2- t1 is then the travel time of the wave to the ground and back to the airplane.
The radio altimeter system consists of radio altimeter Receiver/Transmitter (R/T) unit, radio altimeter antenna, and display.
A radio altimeter is called ‘radio’ rather than ‘radar’ because its transmissions are not pulsed as radar transmissions are. The transmission is a continuous wave with constant amplitude and a frequency-modulated carrier of 4300MHz (C-band).
Travel Time △t
For 300ft
t3
△T
t1
t2
Time
Travel Time For Given Altitude
Figure 12.1
Civil Aviation Flight University of China 5
NBAA 2003
6
LRRA Theory
N来自百度文库AA 2003
During this time travel, the frequency being currently transmitted has changed. At the time of reception of the reflected frequency f1, the current transmitted frequency is now f2,.
Radio altitude outputs from the receiver/transmitter units are transmitted to the flight instrument system display, as well as to the using systems autopilot flight director system, EICAS, ground proximity warning system and central warning system.
Civil Aviation Flight University of China 3
Radio Altimeter ( RA)
NBAA 2003
Each R/T unit transmits RF signal to the ground through a dedicated transmit antenna. The reflected RF signals are received by a dedicated receive antenna and routed to the R/T unit for altitude computation.
Civil Aviation Flight University of China 4
LRRA Theory
NBAA 2003
Frequency 4350MHz
f2
Transmitted Frequ ency
△F f3 △f
f1
4250MHz Difference
Freque ncy
For 300ft Difference Frequency For Given Altitude
NBAA 2003
1
Radio Altimeter ( RA)
NBAA 2003
Radio Altimeter
无线电高度表
Civil Aviation Flight University of China 2
Radio Altimeter ( RA)
NBAA 2003
The radio altimeter system provides accurate terrain clearance altitude information displayed in the flight compartment, for use by the flight crew.
The rate of frequency modulation is 100 times per second. The radio altitude is computed by determining the difference between the frequency of the reflected signal and the frequency of the signal being transmitted at the instant the reflected signal is received.
The radio altimeter is called ‘low range’ because it is not intended to operate at airplane altitudes above ground greater than 2500 feet. Its principal usage is during the final approach and takeoff. By the abbreviation LRRA, we mean “Low Range Radio Altimeter”.
If at time t1, frequency f1 is transmitted to the ground, the same frequency f1 will be received, after reflection, at time t2.
The time difference △T= t2- t1 is then the travel time of the wave to the ground and back to the airplane.
The radio altimeter system consists of radio altimeter Receiver/Transmitter (R/T) unit, radio altimeter antenna, and display.
A radio altimeter is called ‘radio’ rather than ‘radar’ because its transmissions are not pulsed as radar transmissions are. The transmission is a continuous wave with constant amplitude and a frequency-modulated carrier of 4300MHz (C-band).
Travel Time △t
For 300ft
t3
△T
t1
t2
Time
Travel Time For Given Altitude
Figure 12.1
Civil Aviation Flight University of China 5
NBAA 2003
6
LRRA Theory
N来自百度文库AA 2003
During this time travel, the frequency being currently transmitted has changed. At the time of reception of the reflected frequency f1, the current transmitted frequency is now f2,.
Radio altitude outputs from the receiver/transmitter units are transmitted to the flight instrument system display, as well as to the using systems autopilot flight director system, EICAS, ground proximity warning system and central warning system.
Civil Aviation Flight University of China 3
Radio Altimeter ( RA)
NBAA 2003
Each R/T unit transmits RF signal to the ground through a dedicated transmit antenna. The reflected RF signals are received by a dedicated receive antenna and routed to the R/T unit for altitude computation.
Civil Aviation Flight University of China 4
LRRA Theory
NBAA 2003
Frequency 4350MHz
f2
Transmitted Frequ ency
△F f3 △f
f1
4250MHz Difference
Freque ncy
For 300ft Difference Frequency For Given Altitude