Automatic direction finder system Purpose
The automatic direction finder (ADF) system is a navigation aid. The ADF receiver uses amplitude modualted (AM) signals from ground stations to calculate the bearing to the ADF station from the airplane longitudinal axis. The ADF system also receives standard AM radio broadcasts.
Abbreviations and Acronyms
AC - alternating current
AM - amplitude modulated
ACP - audio control panel
ADF - automatic direction finder
AM - amplitude modulation
ant - antenna
app - approach
ARINC - Aeronautical Radio, Inc.
BFO - beat frequency oscillator
Capt - captain
DC - direct current
DEU - display electronics unit
EFIS - electronic flight instrument system
F/O - first officer
gnd - ground
Hz - hertz
LCD - liquid crystal display
LRU - line replaceable unit
nav - navigation
NCD - no computed data
QEC - quadrantal error correction
RBL - right buttock line
Adf system - general description Description
The ADF control panel supplies manual tune inputs to the ADF receiver. The ADF antenna assembly contains the loop antennas and the sense antennas.
The ADF receiver calculates the bearing to the ADF ground stations and sends it to the DEUs for display. The ADF bearing also goes to the radio magnetic indicator (RMI). The ADF receiver processes audio from the ground stations and sends it to the remote electronics unit (REU).
ADF SYSTEM - FLIGHT COMPARTMENT COMPONENT LOCATION
ADF System Components
The ADF control panel is on the P8 aft electronics panel.
Interface Components
These flight compartment components have an interface with the ADF system.
Left and right EFIS control panels
Left inboard and outboard display units
Right inboard and outboard display units
Capt and F/O audio control panels.
Electronic Equipment Compartment
The ADF receiver is in the electronic equipment compartment on the E3-1 shelf.
ADF Antenna
The ADF antenna is on the top of the fuselage at fuselage station 694.
ADF SYSTEM - POWER AND ANALOG INTERFACE
Power
115v ac power from the ADF circuit breaker goes to the ADF control panel. The ADF control panel uses the 115v ac power for operation. The ADF control panel sends 115v ac power to the ADF receiver for operation. The ADF receiver sends 12v dc power to the ADF antenna for operation.
PSEU
The proximty switch electronics unit (PSEU) supplies an air/ ground discrete input to the ADF receiver. The ADF receiver uses the air/ground input to calculate the flight leg count for the internal memory.
ADF Antenna
The ADF antenna assembly contains the loop antennas and the sense antenna. The antenna assembly also contains signal amplifiers for the loop and the sense antenna. The loop antennas supply direction data and the sense antenna supplies station audio.
REU
The ADF receiver sends station audio to the remote electronics unit (REU). The REU sends the station audio to the flight compartment headsets and speakers.
ADF SYSTEM - DIGITAL INTERFACE
General
The ADF receiver has an interface with the display electronics units (DEUs) and the radio magnetic indicator (RMI). The interface is on ARINC 429 data buses.
ADF Control Panel
The ADF control panel sends tune frequency inputs to the ADF receiver. The ADF control panel sends a data word that contains the ADF mode or ANT mode selection. The ADF control panel sets a bit that enables ADF receiver beat frequency oscillator (BFO) operation when you turn on the tone selector.
Digital Output
The ADF receiver sends this data on two output data buses:
ADF station bearing
Test signals
Receiver condition.
Output data bus 1 from the ADF receiver goes to the radio magnetic indicator (RMI). The RMI uses the station bearing data to control the RMI bearing pointers.
Output data bus 2 goes to the DEUs for display.
RECEIVER
Purpose
The ADF receiver calculates bearing to a station that transmits in the frequency range of 190 Khz to 1750 Khz. The receiver also receives station identifiers and AM broadcasts.
Description
The ADF receiver is a standard ARINC 600 3 MCU unit with dimensions approximately 3.7 in. x 7.9 in. x 14.8 in. The receiver weighs approximately 9 pounds and uses 115V ac 400 Hz power for operation. The receiver has a non-volatile flight fault memory. Only shop personnel can use this feature.
Test and Indication
There is a test switch on the front panel of the receiver. When you push the test switch, a self test of the receiver starts. At the end of the test, the status of the receiver and the control panel inputs show on the front panel LED status indicators.
ANTENNA
Purpose
The ADF antenna receives electromagnetic signals from ground stations. The sense antenna receives the electrical part of the signal. The loop antenna receives the magnetic part of the ground station signal.
Description
The antenna assembly is a one piece molded shell. The antenna attaches to the airplane with 12 bolts. The antenna assembly contains these components:
Loop antenna elements (2)
Sense antenna (1)
Electronics assembly.
The ADF antenna electronics assembly contains amplifiers for each of the antenna elements. The amplifiers receive 12v dc power from the ADF receiver.
The electrical connectors connect the antenna assembly to the ADF receiver.
The preferred resistance measurement point uses one of the mounting bolt holes counterbore. There is also an alternate resistance measurement point. The alternate measurement is done from the inside of the airplane.
