Direction Finding S.A.R.

direction finding sar

  • Multi-beacon DF
  • Single compact antenna unit
  • High sensitivity receiver
  • Fully COSPAS-SARSAT compatible

The Techtest DF system is designed to reduce the time to locate emergency locator beacons. It is compatible with both 121.5MHz swept tone distress beacons and 406MHz COSPAS-SARSAT transmissions on current and future frequencies.

The user is able to monitor four frequencies and detect emergency transmissions. Each transmission is allocated a unique identification which can then be selected for more detailed information.

For 121.5MHz the system can display relative bearing details.

For 406MHz the system will give all the same information as 121.5MHz but in addition will record and decode the COSPAS-SARSAT message, giving details of the distress beacon and if available the GPS beacon location.

The system comprises of three modules

  • 1. Antenna (10-246-1) The Antenna is a single compact module comprising a circular array of elements with integral high sensitivity receivers. The array is designed todf control panel give optimal angular resolution of the emitters.
  • 2. Control Unit (406-28) The Control Unit takes the array output and, using a digital processing and advanced beam forming technique, is able to discriminate multiple emitters and direction find on the signals. All the data is processed using intelligent algorithms to reduce system noise and spurious responses.
  • 3. Display (407-3) Different display options are available and are platform specific. The basic display module is based on the Techtest 407-2 unit. This unit is designed for ease of use featuring mode and scroll controls and a dual function uncluttered graphic LCD display. A secondary display option is available.

Detection
In normal operating mode the DF receiver frequency is switched cyclically between 121.5, 156.8 and 243 MHz. If a signal above the threshhold is detected, a 0.3 second snapshot is recorded before continuing. A separate receiver is used to continuously monitor the 406 SARSAT frequency. If a signal is detected then the DF receiver will immediately switch to 406MHz frequency and record a snapshot. In the event of transmitting beacons incorporating a GPS position, the system will display the applicable lat/long co-ordinates.

Direction Finding / Homing
A 360˚ direction finding facility is provided giving a direction for the aircraft to fly to the transmitting beacon. No other navigation aids are required. If however on board GPS navigation systems are installed in the aircraft, system integration will provide aircrew with both an absolute bearing and distance information to the transmitting beacon.
In the Homing mode the system sequentially scans the distress frequencies and provides a visual display of left/right steer information.

Cockpit Controller / Indicator
The controller / indicator is mounted in the cockpit. There are just two controls : a push button mode selector (switching between Decode and DF modes), a rotary click / push selector providing control of menu options. The unit is designed to operate mainly without user input.
The user can select any of three modes:

  • i)    Left-Right Indicator: To show bearing relative to aircraft heading.
  • ii)   Map display: Showing relative positions, (or bearings), of all detected emitters, both from DF receiver and 406 Decoder.
  • iii)  Text Display: Ideal for 406 decoder information. Can also be used to display range and bearing data.pdf icon
Dimensions Short 3/8 ATR (90x198x322mm)
SAR frequencies 121.5, 243, 156.8, 406 MHz
Training frequencies 4 selectable: 110 to 410 MHz
Sensitivity 2.5μV
DF Accuracy Better than 5˚
Decoder Frequency 406.025 - 406.050 MHz
Message Format COSPAS-SARSAT C/S T.001
Supply Volts 18-36V DC MIL-STD 704D
Antenna 10-246-1
Diameter 250mm
Height Standard 250mm
Reduced 180mm
Polarisation Vertical
Cockpit Controller / Indicator 406-3
Dimensions 146 x 67 x 152mm
LCD Display 56 x 42mm (320 x 420 pixels)
Backlighting NVIS Green B (MIL-STD 3009)
Environmental MIL-STD 810F
EMI/EMC MIL-STD 461 F