-the AGC voltages of the LOC and G/S receivers are checked for acceptacle range,
-
both synthesizers (LOC and G/S) are tested for lock/unlock conditions,
-
both anti-aliasing filters (LOC and G/S) are tested for
frequency response. Localizer and Glide Slope failures detected during self-test remain latched until the same test passes on a subsequent self-test execution.
R (3) Not Applicable
1EFF : 001-004, 1 34-36-00Page 24 1 1 Config-1 May 01/05 1 1 1CES 1
R **ON A/C 051-060,
R (2) Internal description
R (Ref. Fig. 008A)
R The ILS receiver consists of five units:
R - the localizer receiver unit
R - the glide slope receiver unit
R - the I/O processor unit
R - the power supply unit
R - the BITE processor unit.
R (3) Operating principle
R (a) Localizer receiver unit
R The localizer receiver unit receives and detects the localizer
R modulated signals in the frequency range from 108.1 to 111.95
R MHz.
R In approach mode, the RF signal received through the dedicated
R antenna is the filtered by a low loss broadband filter, and then
R mixed with the output of the localizer synthesizer. This
R localizer synthesizer receives tuning information from the I/O
R processor, and provides an injection signal which is 20.05 MHz
R below the selected frequency.
R The 20.05 MHz Intermediate Frequency (IF) tuned signal obtained
R at the output of the mixer is applied to a 20.05 MHz crystal
R filter which provides the selectivity for the receiver. It is
R then amplified and mixed with a second injection frequency 20.505
R MHz to produce a 455 kHz signal.
R After 2 stages of amplification, this second IF signal is applied
R to an envelope detector. The output of the envelope detector,
R which only contains the baseband components of the second IF, is
R fed to:
R - the Automatic Gain Control (AGC) amplifier/filter, which
R controls the gain of the different IF amplifiers according to
R the amplitude of the IF output
R - the Input/Output (I/O) processor unit for audio identification
R decoding and localizer deviations computation.
R (b) Glide slope receiver unit
R The glide slope receiver unit receives and detects the modulated
R glide slope signals, in the frequency range from 329.15 to 335
R MHz. Its architecture is similar to the one of the localizer
R receiver, except that the frequency values are different, and
R that there is no audio identification encoded on the G/S signal.
R 1EFF : 051-060, 1 34-36-00Page 25 1 1 Config-1 May 01/05 1 1 1CES 1R ILS Receiver - Block Diagram R Figure 008A
R 1EFF : 051-060, 1 34-36-00Page 26 1 1 Config-1 May 01/05 1 1 1CES 1
R Additionally, the glide slope receiver unit includes a localizer
R and glide slope functional test oscillator/modulator (90 and 150
R Hz tones) which generates three functional test conditions:
R - centered signal condition
R - down/right signal condition
R - up/left signal condition.
R During the down/right and up/left sequence, a 1020 Hz signal is
R added to the localizer 90 and 150 Hz tones.
R The functional test oscillators are kept off except during
R functional tests to prevent possible interference with normal
R operation.
R (c) I/O processor unit
R The I/O processor unit comprises three separate processors:
R - the primary Digital Signal Processor (DSP)
R - the monitor Digital Signal Processor (DSP)
R - the system processor.
R 1 DSPs_
R The DSPs compute the deviation data from the analog outputs of
R the localizer and the glide slope receiver units.
R Each DSP, identically but separately:
R - receives, filters and digitizes data from the glide slope
R and localizer receiver units
R - processes these data and elaborates localizer and glide
R slope deviations (DDM)
R - determines the DC level of the glide slope and localizer
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