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747-400 MAINTENANCE MANUAL
 4)  The input to the frequency module is the 32-bit TM data from the time module. This data consists of time samples for each range bin within a pulse rate interval (PRI). The TM data is received by the buffer, which is enabled only in the windshear mode, then transferred to the corner-turn buffer under control of the address/bus controller. The TM data for each range bin is stored in the corner-turn buffer then sent to the DSP array and processed by doppler shift detection algorithm. The DSP circuitry examines small areas of storm cells with successive pairs of transmitted pulses for doppler frequency shifts, and then computes the auto-correlation between tem. Data received from the time module starts with close range bins and continuing up to the maximum range bin. A write operation into the corner-turn buffer takes place within a 1 microsecond I/O interval.
 5)  The DSP array processes data for all range bins within a block. Data goes from one DSP to the next DSP within the 1-microsecond time interval. The output data is sent to the signal module on the TM DATA bus. In the windshear mode, the signal is processed by the signal module DSP No. 1 and routed to the hazard processor in the range module.
 6)  The hazard processor, in the range module, computes the windshear hazard factor, deteremines the hazard area, and develops the windshear icons to be displayed on the navigation displays. In addition, the hazard processor determines whether the hazard is a caution or a warning alert. The hazard processor is controlled by the master processor and sent to the navigation displays on the ARINC 453 data bus.
 (s) Receiver/Transmitter Antenna Stabilization Functions
 1)  The antenna stabilization system consists of a stabilization processor in the receiver/transmiter (R/T), the tilt control inputs from the WXR control panel (MAN mode) or EGPWS (AUTO mode), pitch and roll attitude signal from the IRS and elevation and azimuth monitor signals from the antenna. The antenna stabilization circuits in the R/T are the synchro module and the stabilization module. A microprocessor in the stabilization module controls the closed loop antenna stabilization system. The MP solves the line-of-sight equation from these inputs and predicts the new position of the antenna elevation. The difference between the predicted position and the desired position is used to drive the antenna elevation motor.
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 2)  The azimuth drive is an open-loop operation. For this, the microprocessor monitors the position of the antenna and generates signals to reverse the direction of scan when the antenna reaches 90 degrees either side of dead ahead. Antenna scan switching is controlled by outputs from a dual triac switch. When the CW input is activated to drive the antenna clockwise, the CW triac switch is enabled to provide a return path for antenna 115 vols ac through the antenna azimuth motor windings that drives the antenna clockwise. Just before the antenna reaches its clockwise limits (+90 degrees) the CW input is deactivated, removing the 115-volt return path. When the antenna reaches the +90-degree limit, the WXR system activates the CCW input, turning on the CCW triac switch to provide a return path for antenna 115 volt ac through the antenna azimuth motor windings that drives the antenna counterclockwise. a) The left R/T receives continuous left and center IRU
 pitch and roll attitude stabilization inputs. The captain's IRS source select switch in the C position sends a discrete ground to the R/T to transfer inputs from the left to the center IRU in the R/T.
 b)  The right R/T receives continuous right and center IRU pitch and roll attitude stabilization inputs. The first officer's IRS source select switch in the center position sends a discrete ground to the R/T to transfer inputs from the right to the center IRU in the R/T.
 (t) System Monitoring
 1)  Control (setting the operating mode, range, tilt, etc.) and monitoring of operational status of the radar system is performed by a microprocessor-based system. During each microprocessor program loop, the 32-bit serial control word is checked to determine the selected mode of operation from the control panel and range selected on the displays. The microprocessor then sends information on the data bus and control bus to set the system to the selected operating conditions. Additionally, during the program loop, selected inputs are checked or compared to determine the operational status of the system. The results of these checks or comparisons are used to control the display of fault warning messages on the NDs.
　
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