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ADF SYSTEM - CONTROL PANEL
ADF SYSTEM - CONTROL PANEL
EFFECTIVITY
SHZ ALL 34-57-00
Page 19
D633A101-SHZ1 Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-57-00-009
Antenna Inputs
The loop antenna contains two identical antenna loops (sine
and cosine) that are mechanically displaced ninety degrees
from each other and share a common ferrite core. The sense
antenna and loop antenna sine and cosine outputs are coupled
through an L- band filter and static protection circuit. The
signals then go to separate but identical low noise, wide
dynamic range FET input amplifiers. The antenna outputs go to
the antenna modulators in the ADF receiver.
ADF Control Panel Inputs
The ADF receiver system processor receives manual tune
inputs and control panel mode selections from the ADF control
panel on an ARINC 429 data bus.
PSEU
The proximity switch electronics unit (PSEU) sends an air
ground discrete to the system processor. The discrete sets the
flight leg count for the fault memory.
Program Pin Inputs
The ADF receivers get program pin discretes from a dip switch.
The bearing computer circuit uses quadrantal error correction
(QEC) program pin inputs to adjust for the signal distortion
caused by the airplane structure.
A discrete identifies the antenna location as a top mounted
antenna.
Receiver Operation
The ADF receiver contains two major assemblies, the A4
receiver assembly and the A2 instrument assembly.
The A4 receiver assembly contains the antenna modulators,
tuner section, and synthesizer.
The modulator receives the input signals from the antenna
assembly. The loop antenna inputs are modulated with a 95 Hz
sine and cosine reference signal produced by the system
processor. The modulated loop antenna signals are then
summed with the sense antenna input. This composite signal
then goes to a preselector filter in the tuner section.
ADF SYSTEM - FUNCTIONAL DESCRIPTION
EFFECTIVITY
SHZ ALL 34-57-00
Page 20
D633A101-SHZ1 Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-57-00-010
The tuner section basically contains the receiver that processes
the antenna inputs. The receiver tunes the frequency range of
190 to 1799 kHz. The tuner section receives the input signals
from the antenna modulators and first sends it through a
preselector filter. This preselector filter is made of six diode
switched bandpass filters that are tuned to a specific portion of
the ADF signal band. The filter is tuned by the system processor
based on ADF control panel tune selections. From the
preselector the signals are mixed with 15.19 through 16.75
MHz signal and an 18.6 MHz signal from the synthesizer. The
signals are also filtered through a 15 MHz and 3.6 MHz to
produce an intermediate frequency that can be processed by
the ADF receiver.
The synthesizer uses binary tune data from the system
processor to produce the injection frequencies to the mixers
in the tuner section.
The A2 assembly contains the system processor, signal
processor, and the maintenance processor. The system
processor provides these functions:
* Format ADF bearing from the signal processor into an
ARINC 429 bearing word
* Provide frequency tuning for the tuner section
* Perform functional test and power up tests
* Provide test results to the maintenance processor
* Transmit equipment identification and frequency data.
* Transmit station identification word and maintenance related
words from the maintenance processor
* Store calibration constants in nonvolatile memory.
The signal processor provides these functions:
* Generate sine and cosine modulation to the ADF loop
antenna modulators
* Receive analog data from tuner section
* Compute relative bearing to the station
* Detect 1020 Hz and 400 Hz identifier tones
* Provide audio output.
The maintenance processor provides these functions:
* Receives data from the maintenance bus inputs, stores time,
date, and aircraft configuration and processes the
maintenance control word.
* Store data from system processor in NVM.
* Determines validity of input maintenance word
* Formats fault summary word and sends it to the system
processor
* Transfers all CMC interactive and normal mode data to
system processor
* Provide maintenance menus in the airplane when requested
by the CMC
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