1eltdf.ppt last revised: 16 july 2002 electronic direction finding developed as part of the national...

1ELTDF.ppt Last Revised: 16 July 2002

Electronic Direction Finding

Developed as part of the National Emergency Services Curriculum Project


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)


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


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


What are you looking for?


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


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


L-Per Receiver


• 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.




• 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.


Using the L-Per


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


DF = Follow the Needle


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)


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


Using the Tracker DF Unit


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


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


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


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


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


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?


Set Up the Equipment Completely

Open the Antennae Fully for use in the field


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


Triangulation• Documenting team movements is logical, and can allow

the team to locate the distress beacon sooner


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!


Plot your Bearings


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


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


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

1eltdf.ppt last revised: 16 july 2002 electronic direction finding developed as part of the national...

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