# Presentation: 185920

## 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

## Slide 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

## What are you looking for?

**Notes:**
ELTs, EPIRBs, and now PLBs both for inland and maritime use.

##  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.

-  L-Per Components Continued

##  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.

##  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