User Guide

Series III Avionics
Pilot's Guide
Page 28
DFS-43A Automatic Direction Finder System
General Description
The DFS-43A Direction Finder System provides reception of low-frequency navigational aids and AM
broadcast stations in the 190.0 – 1860 kHz frequency range.
The DFS-43A System consists of the DF-431B Receiver, the CD-432B Control Display Unit, and the AT-
434 Loop/Sense Antenna. This system provides accurate, dependable reception of enroute
nondirectional beacons (NDB), Locator Outer Markers (LOM), and commercial AM broadcast stations.
Microprocessor circuitry controls operation, processes signals, performs self -calibration, and provides
full-time self -diagnostics. This all digital, solid-state design includes a unique signal filter that provides an
extremely stable needle position even in areas of high RF noise.
Special digital circuitry provides a unique steering command that may be used directly by Electronic Flight
Instrument Systems (EFIS) or in conjunction with the Chelton Avionics VNS-41A VHF Navigation System
for electromechanical HSI course deviation display. Analog outputs for standard ADF indicators and RMI
pointers are included.
The DFS-43A certified frequency range is 190 to 1860 kHz, and the international marine HF distress
frequency of 2182 kHz. Frequency tuning may be done by the CD-432B Control Display Unitor by
external equipment such as an RMS-555 Radio Management System.
The active and standby frequency are displayed on the CD-432B simultaneously and stored in nonvolatile
memory. Switching between the two is done by simply pressing a frequency transfer button below the
displayed frequencies.
Advanced heat sink and cooling fin design efficiently collect and dissipate internal heat of the receiver,
providing cooler operating temperatures and longer unit life.
The AT-434 Antenna unit contains a loop antenna, sense antenna, and a solid-state amplifier. The "front
end" of the receiver is actually in the antenna unit, where received signals are processed, converted to an
intermediate frequency and cabled to the receiver. This minimizes effects of electrical noise, and
eliminates the requirement for critical cable lengths between antenna and receiver.