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Fixed Direction Finding

The Direction Finding works both with 121.5 MHz frequencies and with COSPAS-SARSAT 406 MHz transmissions. The user is able to monitor four frequencies and detect emergency transmissions. Each transmission is assigned a unique identifier which can then be selected for more detailed information.

On 406 MHz the system will provide all the same information of 121.5 MHz, but it will also record and decode the COSPAS-SARSAT message, providing the details of the signal and, if available, the GPS position. The system includes three modules:

  1. Antenna (10-246-1)
  2. Control Unit (406-28)
  3. Display (407-3)



Detection: in normal operating mode the frequency of the DF receiver is switched cyclically between 121.5, 156.8 and 243 MHz. If a signal is detected above the threshold, a snapshot of 0.3 seconds is recorded before continuing. A separate receiver is used to continuously monitor the 406 SARSAT frequency. If a signal is detected, the DF receiver will immediately switch to the 406 MHz frequency and record a snapshot. When transmitting signals that incorporate a GPS position, the system will display the applicable lat / long coordinates.

Search for the direction / search for the reference point: a 360 ° direction search function is provided which allows the aircraft to head towards the transmitting beacon. No other navigation aids are required. However, if GPS navigation systems are installed on board, the system integration will provide the crew with absolute tracking and distance information to the transmitting beacon. In the reference point search mode, the system sequentially scans the rescue frequencies and provides a visual left / right visualization of the information.

Cockpit controller / indicator: the controller / indicator is mounted in the cockpit. There are only two controls: a push button mode selector (switching between Decoding and DF modes), a click / push rotary switch that provides control of menu options. The unit is designed to work primarily without user input.