(3)
The reflected signal is received by the antenna during the interval between transmission pulses, and applied through the duplexer to the receiver circuits of the RT. The limiter protects the receiver from power pulses, allowing low power received signals to the mixer.
(4)
The mixer uses a frequency source oscillator to develop the first IF frequency. The first IF amplifier provides a 25 db gain. The second IF is mixed with frequency source oscillator signals to attain a 13.888 MHz signal. The second IF amplifier gain is controlled by the automatic gain control (AGC) and sensitivity time control (STC) circuits in the azimuth filter.
(5)
The range filter is a low pass filter that also digitizes the signal. The low pass function improves the signal-to-noise ratio of the IF signal. The digitized signal is sent to the azimuth filter, which filters and encodes the signal. The encoded signal is sent to the input/output circuits, and formatted into a 1536-bit data word. A 64-bit control word is added to the data word and sent to the indicator, in serial form.
(6)
In the indicator, the serial data word is converted to TTL format and the data words and control words are separated and stored in buffers. The data word is then stored in memory through a multiplexer. There the data is output to video circuits by a set of parallel to serial shift registers.
(7)
The switches controlling mode, range, tilt, system stabilization, and gain are applied through a control word generator to the central processing unit (CPU) of the R/T. The CPU uses the control words to configure the operating parameters of the system.
(8)
The CPU incorporates a microprocessor to perform its various internal functions. The microprocessor executes its control program, which consists of eight major control routines, 180 times a second. The routines are:
(a)
Attitude routine providing pitch and roll parameters for the stabilization routine.
(b)
Stabilization routine providing elevation position to the elevation maintenance routine.
(c)
Scan maintenance routine providing antenna scan drive.
(d)
Elevation maintenance routine providing antenna elevation drive.
(e)
Control bus manager routine determining proper control configuration.
(f)
Problem control manager routine programming the internal data collection parameters of the R/T.
(g)
Data bus formatter routine processing and assembling the 64-bit control word of the serial word sent to the indicator.
(9)
Input/output circuits provide the electrical interface circuitry for most of the receiver-transmitter rear connector signals. Many of these are routed through the central processing unit. Input/output circuits interface four 12-kHz serial data bus inputs, two 100-kHz serial data bus inputs, and three 1-MHz data bus outputs. Several discretes input are used, including the antenna feedback signals and installation program pins.
(10)
The indicator control circuit is a microcomputer that uses the front panel switch outputs to format a 32-bit word that informs the R/T of the indicator status (view and display selects). The R/T uses this control word to generate antenna control signals and to configure its operation and the data word to the indicator.
(11)
The indicator receives the serial data from the R/T and is converted into control and data words. The control word buffer accepts and holds the control word bits until they are all clocked into the buffer. The control word is then separated into its scan angle and system status components. The scan angle bits are applied to a coordinate converter. The scan angle is shipped to the indicator in a polar coordinate system. The coordinate converter converts the rho, theta coordinates into an X, Y coordinate system. The converter scan angle coordinates are used as address coordinates for the data placed in the memory circuits. The remainder of the control word (system status bits) is applied to the message generator. The system status bits are used to address the memory locations of their corresponding messages. The message is then applied to another memory which contains the binary line information to generate that message.
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Jun 20/86 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 34-41-02 Page 11
B. Functional Description, Antenna Stabilization
(1)
The synchro/digital converter provides an interface for aircraft attitude signals from the attitude reference system and is under total microprocessor control. The microprocessor uses an iterative technique of generating a digital word, and converting it to an analog signal for comparison with a corresponding analog attitude signal. This process is accomplished for two channels, one for pitch and one for roll.
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