(2)
At altitudes above the operational range of the receiver-transmitter, the low level signal coupled between antennas through the external interconnecting coaxial cable is processed through the receiver circuits and detected in the antenna coupling monitor to check the operation of the antenna system. At altitudes within the operational range of the receiver-transmitter, the normal received signal is processed through the receiver circuits and detected in the AGC circuit. The AGC circuit functions to maintain receiver gain and provides a signal to the singal presence monitor. The output from the antenna coupling monitor is applied to the SENS indicator threshold sensor and flag gate circuit. The output from the signal presence monitor is applied to the SENS indicator threshold sensor and flag alarm circuit.
(3)
An output fromm the calibration loop mixer is applied to the power modulation monitor and altitude calibration circuits. If the monitor detects a loss in signal that exceeds tolerances, an output is provided to the flag gates and XMTR threshold sensor signifying improper operation. The calibration circuits will do the same if the amount of altitude correction required is beyond the limits of the self-calibration circuits.
(4)
In the height indicator, the 10-kHz tracer signal to the servo-amplifier is processed to the integrity monitor when the servo is in a nulled state. The detected tracer signal maintains the flag amplifier in the conducting state allowing the flag solenoid to be energized (flag out of view). The tracer signal output from the integrity monitor is also supplied to the receiver-transmitter IND theshold sensor and flag gates. The absence of the tracer signal signifies improper height indicator operation.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
(5)
The inputs to the flag gates must be of sufficient magnitude to inhibit a flag alarm condition. If any one of the inputs drops below a specific value, an output is supplied to the flag alarm circuits which turns off the flag driver causing the height indicator warning flag to come into view and the receiver-transmitter FLAG indicator to illuminate.
(6)
An output from the flag alarm circuit is also provided to the pointer stow circuit. An alarm condition activates this circuit causing the height indicator altitude pointer to freeze in position for approximately 1 second and then to be driven up behind the pointer mask.
(7)
When the airplane is at an altitude of over 2500 feet, or for any condition when received signal strength is inadequate for normal system operation, an input is provided to the flag alarm circuit.
(8)
The receiver-transmitter lights marked WARN (yellow) and FLAG (red) are controlled directly by the warn relay driver and flag alarm functions, respectively. The WARN lamp will light when there is a loss of signal and both the WARN and FLAG lamps will light if a malfunction occurs in the LRRA system. The four neon lights marked SENS, XMTR, COMP, and IND are controlled by the integrity gates. Power is applied to the neon lights only when the PRESS TO MONITOR button is pressed. Pressing this button will cause one or more of the neon lamps to light identifying the area in which a fault has occurred.
(9)
No OFF control is provided in the LRRA system. Each LRRA system in the dual R/T system is turned on and off independently at the P18-1 overhead panel circuit breaker RADIO ALT-1 or the P6-1 overhead panel circuit breaker RADIO ALT-2, as required.
C. Program Pin Selection (R/T and EFIS)
(1) Input program pins select modes of operation of the R/A as follows:
(a)
The system select input selects the system modulation rate.
(b)
The aircraft installation delay (AID) program pins are jumpered for 57 feet. This calibrates the system so that the altitude readout is zero at touchdown. It compensates for the length of the antenna cables plus fuselage to ground distance.
(c)
The indicator status pins are used for an external display. They are grounded because the system does not use an indicator other than the EADI.
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