l-per direction finding modified from hawk mountain civil air patrol 8-apr-06
TRANSCRIPT
L-Per Direction FindingL-Per Direction FindingModified fromModified from
Hawk MountainHawk MountainCivil Air PatrolCivil Air Patrol
8-APR-068-APR-06
ObjectivesObjectives
• ELT Basics
• The Old Little L-Per
• DFing with the L-Per
• Hands-on Training
ELT Basics: The FlavorsELT Basics: The Flavors
• ELT – Emergency Locator Transmitter– aircraft
• EPIRB – Emergency Position Indicating Radio Beacon– boat
• PLB – Personal Locator Beacon– hiker
ELT Basics: The FlavorsELT 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 FrequenciesELT 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 FrequenciesELT 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 OutputELT Basics: The Output
• 121.775 MHz
– Continuous Transmission– Swept Tone
The Old Little L-PerThe Old Little L-Per
ControlsControls
• Mode Switch– Turns the unit OFF– Selects DF mode– Selects REC mode
• The Mode switch determines how the L-Per operates
ControlsControls
• 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
ControlsControls
• 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)
ControlsControls
• 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
ControlsControls
• 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 NotesGeneral 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 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 OperationTwo 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 DFREC vs DF
• REC = RECEIVE 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 ModeDF 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 ModeDF Mode
• Always turn in the direction the needle points
• If the needle points right, turn right
• If the needle points left, turn left
DF ModeDF 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 ModeDF 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 ModeREC 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 TechniquesREC 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 TechniquesREC 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…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…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…
• 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-PerThe 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 & PropagationReflections & 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 & PropagationReflections & 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 How do you take a compass reading?compass reading?
Compass HeadingCompass 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 HeadingCompass 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 HeadingCompass 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 RECCompass 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 DFCompass 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 TricksOld Little L-Per Tips ‘n Tricks
• The unit runs on two 9v batteries – only 1 is needed for operation
The Future of ELTsThe Future of ELTs
Changes are in progress!Changes are in progress!
Future of ELTsFuture 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-PerThe New Little L-Per
The New Little L-PerThe New Little L-Per
The New Little L-PerThe New Little L-Per
The New Little L-PerThe 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-PerThe 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