BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 6.  Antenna_______
 A.  The antennas are linearly polarized horns. Two identical antennas are used in each system of the dual LRRA system, one for transmitting and one for receiving. The antennas are connected to the receiver-transmitter through specific length coaxial cables and are flush mounted on the lower fuselage centerline as follows:
 TRANSMIT ANTENNA NO. 1 STA 450 RECEIVE ANTENNA NO. 1 STA 430
 TRANSMIT ANTENNA NO. 2 STA 390 RECEIVE ANTENNA NO. 2 STA 410

 B.  A specific length coupler (delay line) cable is connected between each receive and transmit antenna.
 C.  Altitude Measurement Operation
 7.  Operation (Fig. 2)_________
 A.  Altitude Measurement Operation
 (1)  
The LRRA system provides altitude data when power is applied by separate circuit breaker to the receiver-transmitters. Low voltage power is then supplied to all circuits in the receiver-transmitters and to the height indicators. Each LRRA system is turned on by closing its circuit breaker. Each LRRA system (LRRA1 - Captain's, LRRA2 - F/O's) operates independently of the other.

 (2)  
An oscillator in the R/T modulator generates a 155-Hz modulation signal. This signal is wobbulated by a 31-Hz input signal from the wobbulation generator and then applied to a generator which produces the triangular wave modulating signal for the R/T transmitter.

 (3)  
The signal from the modulator frequency modulates an oscillator signal in the R/T transmitter. The resultant signal is amplified and frequency multiplied to produce the nominal 4.3-GHz transmitter output signal.

 (4)  
A portion of the transmit signal is coupled to the AFC circuits. The AFC loop acts to hold the center frequency of the transmitted signal to 4.3 GHz. Another sample of the transmitted signal is coupled to the calibration loop mixer and delay line. The resultant difference frequency output from the calibration loop mixer is applied to the calibration circuits where it is converted to a dc voltage (altitude). This voltage is compared to a standard reference voltage and any difference is sensed and applied to the modulator for altitude self-calibration. The calibration is accomplished by varying the slope of the triangular wave to reduce the calibration circuit difference (error) signal to zero.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
115V AC.AFDS WARN
LRRA-1 .DC ALT (AUX)
ELEX .DC ALT (AP/AT)
.VALID
.AFDS WARN

PWR DH
.VALID .VALID
BUS-1
.DC ALT (AP/AT).DC ALT (AP/AT)P18-1 PANEL
CAPT'S ADI FCC-A
AUTOTHROTTLE CMPTR .DC ALT (AUX).VALID
.DC ALT (AUX)
.ALT TRIPS
XMIT DH .DC ALT (AUX)
(500') .DC ALT-1 (AUX)
.DC ALT
YAW DAMPER CONTROLANT-1
.VALIDC GS DISENGAGE (AUX)CKT
.VALID-1 P
.VALID
.TEST INHIBIT
RCV.TWO ALT TRIPS

TEST
.TEST LRRA-1
L
ANT-1 (10')
R
.DC ALT-2 (AUX)
GND PROX CMPTR (INPUTS
FROM LRRA-1 ONLY)
.VALID-2LRRA-1 R/T
CAPT (LRRA-1)INDINSTRUMENT
ARM
GS ENGAGE
SIG

ENG 1
COMPARATORS824
ENG 2 FLT INSTR ACC UNIT
ARM

S826 SIG

.DC ALT-1 (AUX)(CONTROL STAND)REVERSE THRUST ARM .VALID-1
.TEST LRRA-2
115V AC TWO ALT TRIPS
LRRA-2

.DC ALT-2 (AUX)
ELEX (10').DC ALT
TEST
PWR (AUX).VALID-2
BUS-2

.VALID
.AFDS WARNDH

TCAS COMPUTER
P6-1 PANEL .DC ALT (AP/AT)
F/O (LRRA-2)
.DC ALT (AUX) IND
.VALID
XMIT
ANT-2.ALT TRIPS

.AFDS WARN
(500').DC ALT (AUX) DH P
C
.VALID L
RCV .VALID
ANT-2 .DC ALT (AP/AT)

R
(DRIVE) FIRST OFFICER'S ADI FCC-B
LRRA-2 R/T

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