L-Per Direction Finding Modified from Hawk Mountain Civil Air Patrol 8-APR-06

Objectives ELT Basics The Old Little L-Per DFing with the L-Per Hands-on Training

ELT Basics: The Flavors ELT – Emergency Locator Transmitter aircraft EPIRB – Emergency Position Indicating Radio Beacon boat PLB – Personal Locator Beacon hiker

ELT Basics: The Flavors No matter what you call it… Transmits on a distress frequency Indicates the position of an emergency by means of direction finding or GPS Can be manually or automatically activated Throughout this session, ELT will be used generically to also include PLBs & EPIRBs

ELT Basics: The Frequencies 121.5 MHz Civilian Emergency Aircraft Channel 243.0 MHz Military Emergency Channel 406 MHz New Emergency Satellite Channel ELTs can operate on just 1 or ANY combination of the above frequencies

ELT Basics: Training Frequencies To practice, we have our own set of frequencies: 121.775 MHz 121.6 MHz (No Longer Authorized) 243.55 MHz (Proposed) There is no 406 MHz training frequency

ELT Basics: The Output 121.775 MHz Continuous Transmission Swept Tone

The Old Little L-Per

Controls Mode Switch The Mode switch determines how the L-Per operates Turns the unit OFF Selects DF mode Selects REC mode The Mode switch determines how the L-Per operates

Controls Channel Switch Selects the channel you wish to receive If a position is blank – assume that there is no crystal installed Units will have different channel options depending on which model your L-Per is

Controls Sensitivity This control is used to reduce the sensitivity of the receiver. Always start with this at MAX Reduce as you get closer to your target (more details later)

Controls Volume Set to a comfortable level Keep as low as possible (and still hear the ELT) because… Higher volumes reduce battery life Volume has no effect on the indication on the meter

Controls Dial Light switch Lights the meter Keep off unless operating at night Easy to bump the switch and not notice it in the daylight Reduces battery life

General Operation Notes ALWAYS TURN A FULL CIRCLE BEFORE TAKING A COMPASS HEADING Use both REC and DF modes to verify the headings Hold the L-Per with two hands at a full arm’s length, keep the mast perpendicular to the ground Avoid power lines, large metal objects such as vehicles, buildings and signs when taking readings Keep other team members at least 10 feet away when trying to determine headings ALWAYS TURN A FULL CIRCLE BEFORE TAKING A COMPASS HEADING

If you can’t hear it… If you can’t hear the ELT swept tone You are too far away from the ELT The ELT is broken May be transmitting no audio or a continuous tone There is no ELT transmitting Unless you know for sure that the ELT is malfunctioning – don’t believe your L-Per readings

Two Modes of Operation The Little L-Per has two modes of operation Each mode has its strengths and weaknesses Always use both to determine a heading Both modes should point you in the same direction, if not something’s up!

REC vs DF REC = RECEIVE MODE DF = DIRECTION FIND MODE More sensitive Allows you to take headings further away from the ELT No front/back ambiguity Less Accurate DF = DIRECTION FIND MODE Not as sensitive as REC Very accurate readings even at close range Front/back ambiguity exists More accurate headings than REC

DF Mode The meter tells you what DIRECTION THE ELT IS COMING FROM Objective is to center the needle on the meter Centered needle indicates the ELT is directly in front of or behind you

DF Mode Always turn in the direction the needle points If the needle points right, turn right If the needle points left, turn left

DF Mode When the needle centers, the ELT is directly in front of you or directly behind you There is a way to determine if it’s in front of or behind you…

DF Mode To determine if the ELT is in front of or behind you… Remember, the needle always points in the direction of the ELT Turn slightly in one direction If the needle moves in the OPPOSITE direction you are facing the ELT (re-center the needle before taking a compass heading) If the needle moves in the SAME you were not facing the ELT, continue turning until the needle centers again, then re-check before taking the heading

REC Mode The meter tells you HOW STRONG THE SIGNAL IS Objective is obtain maximum signal reading Max meter reading is to the right of the meter In REC Mode Strongest reading occurs when ELT is off the LEFT side of the antenna (YOUR LEFT when holding the L-Per)

REC Mode Techniques Start with Sensitivity at MAX Reduce the Sensitivity so the needle is at mid-scale Turn in a circle Continue to turn in a circle – watch for meter readings that exceed mid-scale

REC Mode Techniques When a reading exceeds mid-scale, reduce the sensitivity to re-center the needle Keeping the highest reading at mid-scale makes it easy to determine if anything exceeds your previous highest reading Find the one spot that has the highest meter reading If you’ve followed this procedure, the highest reading you’ll see is mid-scale, everything else will be less than that At the highest meter reading, take a heading

What if… You get more than 1 direction you feel the ELT is coming from? You can hear the ELT but can’t get the L-Per to “tell” you a good heading? REC and DF mode don’t agree?

Then try… Double check your instrument settings Have someone else double check your instrument settings Try a different location You don’t have to move far (sometimes) Radio waves at 121.5 MHz have a wavelength of about 8 feet

IF you can’t hear the ELT… If you can’t hear the ELT that means: There is no ELT transmitting You are too far from the ELT to hear it The ELT is malfunctioning and not producing the swept tone You or your L-Per are having difficulties… As a general rule, if you can’t hear the ELT’s swept tone, you shouldn’t trust the L-Per’s meter readings

The Old Little L-Per The Old Little L-Per may produce needle movements with no ELT signal present It may track random noise sources or interference from other radio transmitters

Reflections & Propagation Generally VHF radio waves travel in line of sight The waves will reflect off of many objects Its possible to get closer to the ELT and no longer be able to hear it

Reflections & Propagation Ideally radio waves propagate equally in all directions from an ELT antenna Terrain, buildings, damage to the antenna can all cause the propagation to favor one direction over another

How do you take a compass reading?

Compass Heading Once you determine what direction the ELT signal originates from Take a compass heading Record the information Radio the information back to IC Plot the heading on a map IC will plot the heading on a map

Compass Heading A second person must be used to take the compass heading The compass person should only approach the L-Per operator after the operator is sure of the ELT direction

Compass Heading The compass person needs to know whether the L-Per is in REC or DF Mode How you measure the heading does not change between modes How you interpret the heading does change

Compass Heading in REC Shoot your azimuth standing on the right of the L-Per operator Sight your compass over both antennas Your compass reading is the magnetic heading toward the ELT

Compass Heading in DF Shoot the azimuth standing on the right of the L-Per Operator Sight your compass over the two antennas Add 90 Degrees to the compass reading for the magnetic heading toward the ELT

Old Little L-Per Tips ‘n Tricks The unit runs on two 9v batteries – only 1 is needed for operation

Changes are in progress! The Future of ELTs Changes are in progress!

Future of ELTs COSPAS-SARSAT will no longer monitor 121.5 or 243 MHz as of: February 1, 2009 All ELTs must switch to 406 MHz 406 MHz will be the only frequency monitored by the satellites 406 MHz ELTs will also transmit on 121.5 and/or 243 MHz for local homing

The New Little L-Per

The New Little L-Per

The New Little L-Per

The New Little L-Per Very similar in operation to the Old Little L-Per The Sensitivity Control has been eliminated Frequency Programmable No Crystals to buy! 108-174 MHz and 215-270 MHz standard It floats!

The New Little L-Per The Old Little L-Per has not been available for some time New purchases will likely be toward the New Little L-Per Production started in early 2006 Current price $750