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Electronic Direction Finding

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  1. Electronic Direction Finding Developed as part of the National Emergency Services Curriculum Project

  2. How the Mission Starts • ELT set off by plane crashing, or EPIRB goes off when ship sinks or when either is accidentally set off • 97 to 99 percent of all ELT missions are false alarms • SARSAT or COSPAS receives the signal • The satellite transmits the mirror locations of the target to a Local User Terminal (LUT)

  3. How the Mission Starts Continued • The LUT forwards the information to the Mission Control Center so that the appropriate Rescue Coordination Center can be notified • AFRCC, at Langley AFB, calls the mission coordinator or designee who proceeds with the callout

  4. Distress Beacon Frequencies • Primary: • 121.5 MHz, and its harmonics (243 MHz) • 243 MHz, military frequency • 406 MHz, next generation distress beacons transmitting location, tail number or boat identification, etc. • Training: • 121.775 MHz • Required by FAA as of 31 January 1998 • 121.6 MHz is no longer authorized for training

  5. What are you looking for?

  6. L-Per Components • Receiver: the actual metal box, has 7 features: • Dial: indicates signal strength or direction depending on whether in REC or DF mode • Mode switch: sets into DF, REC or OFF positions • Frequency selector: allows the selection of the frequencies possible depending on what is installed and the model

  7. L-Per Components Continued • Sensitivity switch: a variable switch that adjusts the receiver's sensitivity. The closer to the target the less sensitivity is required • Volume control: adjusts the audible signal • Speaker: emits the audible signal • Dial light switch: turns the dial light on for use in low light conditions

  8. L-Per Receiver

  9. L-Per Components Continued • Mast • The two piece wooden vertical mast is joined in the middle by a bolt and wing nut, allowing the mast to be folded for storage or while the unit is carried through the woods. • Make sure to hold the mast on both levels because the L-Per tends to be a knuckle-buster. • The coaxial cable for connecting the radio to the antenna, and mounting screws for attaching the receiver to the mast are mounted to the mast.

  10. L-Per Components Continued • Antenna crossbar • Antenna elements are attached to the crossbar, varying in size according to the frequency that you are searching on • Wire leads connect the antenna elements together at the switchbox located in the middle of the crossbar. • The antenna elements fold down parallel to the crossbar for storage or carrying through the wilderness.

  11. Using the L-Per

  12. L-Per in DF Mode • DF mode measures equal strengths of signal • Not completely accurate, but good enough! • When needle is centered, ELT could be either direction • Needle always POINTS to the ELT (DF=Follow the needle) • Use a TURN to TELL if the ELT is in front or behind you

  13. DF = Follow the Needle

  14. L-Per in REC Mode • Receive Mode Measures Signal Strength only • Signal comes from the direction of the arrows on the antenna (to your left)

  15. L-Per in REC Mode Continued • Use it with multiple centers (more than 2) to verify strongest path • Due Reflections • That’s most likely the true direction to the ELT

  16. Using the Tracker DF Unit

  17. Tracker Operating Instructions • Unfold antennae of the receiver unit, front antennae first then rear antennae • Start the receiver by pressing ON-button. • When turning on the receiver, it will automatically select the international distress frequency (121.5 MHz), channel 1, and the green lights start blinking on the LED display • Use the CH button switch between the distress and practice frequency

  18. Tracker Operating Instructions Continued • By Pressing the MAN button you can choose manual operation instead of automatic. • The MAN light will be lit when this mode has been selected • Receiver sensitivity can be adjusted in the manual mode • In manual or automatic mode, the LED display reflects signal strength in the direction of the signal beacon

  19. Body Shielding • A method of beating reflections at close range • Can use L-Per • Radio Shack JETSTREAM radio is better and CHEAP! • Body blocks out the signal • Called a NULL • Null should be at your BACK

  20. Body Shielding Continued • At extremely close range, a 2m VHF radio un-squelched may work • This works ok when trying to figure out a particular aircraft on a flight line, it will probably not identify a particular hangar

  21. Line of Sight Transmission • ELTs are limited to Line of Sight propagation and reflections • You don’t always need to hear the ELT • Carrier wave may be broadcasting with no audible sweep

  22. What Else Can Affect An ELT Signal? • Power lines • Fence Line (signal can follow) • Reflections off of obstacles • Hangars • Moving Target • Not using the Equipment Properly - See Picture at Right What’s wrong with this?

  23. Set Up the Equipment Completely Open the Antennae Fully for use in the field

  24. Reflections • To beat reflections • Check sensitivity often • Use REC mode • Usually strongest signal is not a reflection • Use the rubber ducky antenna when sensitivity is low • Re-trace your steps if necessary, going back to locations of strong signal strength

  25. Triangulation • Documenting team movements is logical, and can allow the team to locate the distress beacon sooner

  26. Triangulation Continued • You must be able to receive the signal • Center up DF unit on the signal • Take the magnetic bearing (shoot an azimuth) • Correct for magnetic variation • East is least, West is best • Plot your bearings (draw a line) on map • The ELT should be where the lines cross!

  27. Plot your Bearings

  28. What information is needed for the IC? • Make • Model and Model # • Manufacturer • Location Description • Approximate location (Latitude & Longitude) • Owner • Tail Number or Boat Name and Number • Time Found and Time Shut-off

  29. What information is needed for the IC? Continued • Switch Position on ELT or EPIRB: ON, OFF, or ARM • Manufacture Date • Battery Expiration Date • Information which could indicate reason for accidental or justified activation of ELT or EPIRB • NOTE: If you can’t get certain information, don’t worry, the AFRCC understands

  30. Electronic Direction Finding Tasks • Ground Team Members • O-0301: Determine Distress Beacon Bearing • O-0302: Locate a Distress Beacon • Ground Team Leaders • O-0303: Deactivate a Distress Beacon • O-0304: Triangulate on a Distress Beacon

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