Transcript L-per Direction Finding

L-Per Direction Finding
Modified from
Hawk Mountain
Civil Air Patrol
8-APR-06
Objectives
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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
– 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 LPer 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
– 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 midscale, 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 LPer 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
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 LPer
– 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