(g)
TILT control is available with the STAB switch in either position. The TILT control potentiometer receives 10v ac excitation from a transformer in the antenna. Rotation of the TILT knob (on the indicator) causes a change in the amplitude and phase input to the elevation synchro stator windings which determines the angle of the radar beam relative to the horizon.
(h)
The output from the rotor winding goes to the R/T. The signal is amplified by the ELEV AMP and provides the control phase input to the elevation motor. The motor drives the antenna to the desired tilt and is mechanically connected to the tach and elevation synchro. The tach provides rate feedback to the ELEV AMP for smooth operation. When the antenna is tilted the proper number of degrees, the rotor of the elevation synchro is repositioned to a point where the output is no longer unbalanced. The elevation motor then stops.
(2)
Receiver/Transmitter
(a)
The system trigger, received from the indicator in the WX, CYC, and MAP modes, is applied to the Mod Trig Ct, where it is shaped and sent on to the modulator which develops the required high level pulses to turn on the magnetron. These pulses cause the magnetron to generate RF pulses at a frequency of 9345 MHz. The RF pulse widths are 1.0 microsecond in map mode for the 10, 25, 50 and 100 nm ranges, and 3.5 microseconds for all other modes and ranges.
(b)
The antenna radiates the RF energy. The reflected RF energy from targets is received by the antenna. The antenna then directs this energy, via the waveguide, to the receiver circuits in the R/T thru the circulator. The TR limiter at the output of the circulator protects the receiver from high power transmitter pulses leaking through the circulator.
(c)
The received 9345 MHz is applied to the mixer along with a 9285 MHz local oscillator frequency to produce a 60 MHz IF frequency.
(d)
The local oscillator is maintained at exactly 60 MHz below the magnetron frequency by the automatic frequency control (AFC) circuits. The AFC mixer circuits receive samples of the actual magnetron frequency plus the local oscillator output. If the magnetron frequency drifts, a difference frequency will be applied to the AFC circuit, which will retune the local oscillator to 60 MHz below the magnetron frequency.
(e)
The 60 MHz mixer output is applied to an IF amp and video detector circuit along with the STC gate and video blanking pulse.
(f)
The STC gate reduces the sensitivity of the receiver for close-in targets; the video blanking circuit blanks the indicator display during the transmission interval.
(g)
The detected video is passed on to the indicator and automatic gain control (AGC) circuit. When the gain control knob on the indicator is in PRESET, the AGC circuit controls the gain of the receiver.
(h)
Power supply failure, overtemperature and modulator fault (when sensed by the modulator fault detector) will deenergize relay K1 and disconnect power to the radar.
(i)
For maintenance purposes, a MOD ON PUSH/MOD OFF PULL switch is included in the R/T to activate/deactivate the modulator in the R/T and prevent radar pulse transmission from the antenna. Access to this switch requires removal of the R/T dust cover. When the dust cover is in place, the modulator on-off switch is interlocked in ON position.
(3)
Indicator
(a)
The weather radar system indicator unit is a high resolution color indicator which displays weather, operating mode, and fault information on a 5-inch CRT. The CRT uses an X-Y raster scan.
(b)
The indicator contains the video digitizer, level conversion, and second video amplifier circuits, a 5-inch CRT with its associated high voltage power supply, and self-test, range mark, electromagnetic deflection, and sweep circuits. It is self-contained except for dc control signals from the receiver-transmitter.
(c)
The indicator uses digital circuits, integration/averaging, and memory storage to provide a low noise non-fading display. The digital display is refreshed at a 60.7 Hz frame rate by video information stored in memory. The solid state memory holds the image between sweeps, with the data sweep displayed on the CRT moving in synchronism with the antenna's scan.
5B8
Feb 20/85 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 34-41-0 Page 7
Weather Radar Scan Display and Antenna RF Beam Pattern 5D8
34-41-0 Figure 2 Jun 20/84
Page 8
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
5B8
Feb 20/85 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 34-41-0 Page 9
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