R (b) A synthesizer which produces fixed and variable frequencies used
R in the receiver.
R (c) A backplate which provides interface between the rear connector
R and the other assemblies.
R (d) An input/output assembly for interface with the aircraft
R circuits.
R (e) A processor which generates the basic clock signals used and
R converts the analog bearing into digital data for the
R input/output assembly.
R (f) A preprocessor which generates the 96 Hz reference signal used to
R modulate the signals from the loop antenna.
R (g) A power supply assembly which converts the 115VAC aircraft supply
R into the various voltages used by the internal circuits of the
R receiver.
R (4) Operation
R (Ref. Fig. 006B)
R The loop antenna outputs are amplitude modulated by 96 Hz signals
R which are shifted 90. with respect to the other. The modulated
R outputs are then combined to produce a composite signal. The phase
R relationship between this composite signal and the 96 Hz modulation
R is proportional to the bearing of the received station but with a
R phase shift of 180.. The phase shift is eliminated by combining the
R composite signal with the output from the sense antenna. The combined
R output is then filtered and mixed with an injected input from the
R synthesizer to produce a 15 MHz IF output. The injected input to the
R mixer is tunable over the range 15.19 to 16.75 MHz corresponding to
R the receiver tuning range of 190 to 1750 kHz.
R The 15 MHz output is then mixed with a fixed 18.6 MHz signal from the
R synthesizer to produce a 3.6 MHz IF signal which is filtered and
R applied to a coherent detector which provides:
R - an audio output to the aircraft audio integrating system
R - an Automatic Gain Control (AGC) signal for the IF stages
R - a composite audio output which is applied to the signal processor
R through an A/D converter.
R The signal processor determines the phase relationship between the 96
R Hz signal and the composite audio output. The phase data, after
R correction for quadrantal error, is the station bearing data which is
R applied to the input/output processor for transmission through ARINC
R 429 data buses to the DMCs.
R 1EFF : 052-052, 1 34-53-00Page 31 1 1 May 01/05 1 1 1CES 1
R ADF Receiver - Simplified Block Diagram
R Figure 006B
R 1EFF : 052-052, 1 34-53-00 Page 32
1 1 May 01/05
1 1
1CES 1
**ON A/C ALL
(5) Digital outputs
This table contains all the output parameters in the digital form. ----------------------------------------| LABEL | PARAMETER DEFINITION | ----------------------------------------| 032 | ADF FREQUENCY | ----------------------------------------| 162 | ADF BEARING | ----------------------------------------| 254 | ADF IDENTIFIER WORD 1 | ----------------------------------------| 255 | ADF IDENTIFIER WORD 2 | ----------------------------------------| 377 | EQUIPEMENT IDENTIFIER | ----------------------------------------| 356 | MAINTENANCE STATUS | ----------------------------------------
B. Loop and Sense Antenna (Ref. Fig. 007) The combined loop and sense antenna operates in the 190 to 1750 kHz frequency range and consists of the following components enclosed in a fiberglass housing:
-a vertically polarized sense antenna which is omnidirectional in the horizontal plane
-two horizontally polarized orthogonal loop antennas which are directional in the horizontal plane
-
a test loop which enables a self-test of the antenna
-
a printed circuit board which contains three pre-amplifiers used to amplify the loop and sense antennas signals. The pre-amplifiers are energized by plus or minus 12VDC form the ADF receiver.
The output impedance of the antenna is 78 Ohms and the Voltage Standing Wave Ratio (VSWR) 1.2:1.
6. Operation
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