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Fig 24-3 LRRA system theory
[4]The LRRA transmits a signal from the transmit antenna and the reflected
signal is returned to the receive antenna. The antenna is connected to the R/T by
a coax cable whose length is critical. Each antenna is held in place by 8 screws
and has a keying pin to insure correct orientation.Transmit and receive antenna
are identical and are interchangeable.
Fig 24-4 LRRA antenna
[5] The EADI displays the radio altitude for use primarily during approach and
landing. Radio altitude is displayed digitally for altitudes between-20 and 2500
feet. From-20 to 100 feet the display updates in 2-foot increments; between 100
and 500 feet the display updates in 10-foot increments, and from 500 to 2500
feet the display updates in 20-foot increments. Above 2500 feet the display is
blank. If the radio altitude is greater than 1000 feet for greater than 2 seconds
the standard readout is displayed. The complete RA dial represents a radio
altitude of 1000 feet.The invalid radio altitude is indicated by a yellow RA flag.
(see figure 24-5).
Fig 24-5 LRRA EADI display
[6] The LRRA may be tested by pushing and holding the self-test switch on the
front of the receiver/transmitter. When the self-test is activated, the
receiver/transmitter sends both an altitude of 40 feet and an RA invalid signal to
all systems. When the test switch is pushed, the radio altitude display on the
EADI will increase and may show 40 feet momentarily. After approximately 2
seconds, the EADI will show an RA flag until the test button is released. If the
self-test is okay, the status light on the receiver/transmitter will come on after a
2-second delay and will remain on until the switch is released.
EXERCISE
A. Find out the explanations of the following words in your "English-Chinese
technical dictionary"
1. final approach [P1-29 ]
2. coaxial cable [ P1-31 ]
3. blank display [ P1-20]
B. Translate lesson 24 first paragraph and third paragraph into Chinese
C. Explain the following abbreviations
1. LRRA
2. EFIS
3. EADI
READING MATERIAL
LESSON 25
DISTANCE MEASURING EQUIPMENT
VOCABULARY
1. DME = Distance Measuring Equipment 測距儀
2. slant range [ sla:nt ] [ reind ] 斜距
3. facility [ f'siliti ] n. 設備; 裝置
4. measure [ 'me  ] v. 測量; 測定
5. elapsed time [ i'læps ] 經過(消逝)的時間
6. propagation velocity [ pr p'gein ][vi'l siti ] 傳播速度
7. multiplied by [ 'mltiplaid ] 乘以
8. divided by [ di'vaidid ] 除以
9. factor [ 'fækt ] n. 系數; 因數
10. traverse [ 'træv:s ] v. 通過; 經過
11. twice [ twais ] n. ; ad. 兩次
12. tune [ tju:n ] v. 調諧; 調整…的頻率
13. nautical miles [ 'n :tikl ][ mail ] 海里(=1853.2 米)
14. however [ hau'ev ] ad. conj. 可是; 然而; 無論如何
15. program pin [ 'prougræm ][ pin ] 程序銷釘
16. fault [ f :lt ] n. 故障;失效
17. stop [ st p ] v. n. 停止
18. valid [ 'vælid ] a. 有效的; 正確的
19. enclose [ in'klouz ] vt. n. 封入; 裝入
20. ATR = Austin Trimbull Radio 是一家無線電公司
21. secure [ si'kju ] vt. 保證; 固定
22. hold-down [ hould ][daun ] 下壓
22. rear-mounted [ ri][ 'mauntid ] 背面安裝的
24. radiate [ 'reidieit ] v. 輻射; 發射
25. blade-type [ bleid ][taip] 刀型(的)
26. nominal impedance [ 'n minl ][ im'pi:dns ] 額定阻抗
27. VSWR = Voltage standing wave ratio 電壓駐波比
28. moisture [ 'm ist ] n. 濕度; 潮氣
29. screw [ skru: ] n. 螺釘
30. tenth [ ten ] n. a. 第十(的); 十分之一(0.1)的
31. hundredth [ 'hndrd ] n. a. 第一百(的); 百分之一(0.01)的
32. agility [ ' d iliti ] n. 快速; 敏捷
33. RDDMI = Radio Direction Distance Magnetic Indicator
無線電方向距離磁指示器
34. magnetic wheel [ mæg'netik ][ hwi:l ] 磁輪
TEXT
[1] The distance measuring equipment (DME) system provides the flight crew
and associated systems with the slant range to a selected navigation facility.
The DME system
measures the distance
to the selected navigation
station by transmitting a
pulse pair signal, DME
determines the elapsed
time between transmission
from the airplane and the
receiving of that signal
retransmitted from the
ground station. The slant
range is then the
propagation velocity of
the pulse pair multiplied
by the time divided by 2.
The factor of 2 is
necessary because the
pulse pair must traverse
the distance twice, first
down to the station, and
then back to the airplane.
　
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