LPer Direction Finding

1
L-Per Direction Finding

• Hawk Mountain
• Civil Air Patrol
• 8-APR-06

2
Objectives

• ELT Basics
• COSPAS-SARSAT
• The Old Little L-Per
• DFing with the L-Per
• Polarization, Reflections, Broken ELTs
• Future of ELTs
• The New Little L-Per
• Hands-on Training

3
Instructor - Justin L. Ogden

• 1LT, CAP
• CAP member for 12 years
• ARM, GRM, GTM3, MRO, UDF
• Dep. Comm. for Cadets 1303
• Assistant Commo for Group 2

• Ham Radio - N3OG
• Electrical Engineer for General Dynamics

4
ELT Basics The Flavors

• ELT Emergency Locator Transmitter
• aircraft
• EPIRB Emergency Position Indicating Radio
  Beacon
• boat
• PLB Personal Locator Beacon
• hiker

5
ELT Basics The Flavors

• No matter what you call it
• Transmits on a distress frequency (1 to 3)
• Indicates the position of an emergency by means
  of direction finding or GPS
• Can be manually or automatically activated
• Throughout this course, ELT will be used
  generically to also include PLBs EPIRBs

6
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

7
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

8
ELT Basics The Output

• 121.5 243.0 MHz
• Continuous Transmission
• AM Modulation
• Swept Tone
• 50 to 100 milliwatts RF output

• 406 MHz
• Data Bursts
• ½ second long transmission every 50 seconds
• 5 watts RF output

9
COSPAS - SARSAT
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COSPAS SARSAT Organization

• International Organization
• Mission Statement
• The Cospas-Sarsat Programme assists search and
  rescue (SAR) activities on a worldwide basis by
  providing accurate, timely, and reliable distress
  alert and location data to the international
  community on a non-discriminatory basis.

11
COSPAS SARSAT Organization

• Objective
• The objective of the Cospas-Sarsat system is to
  reduce, as far as possible, delays in the
  provision of distress alerts to SAR services, and
  the time required to locate a distress and
  provide assistance, which have a direct impact on
  the probability of survival of the person in
  distress at sea or on land.

12
COSPAS SARSAT Organization

• Strategy
• To achieve this objective, Cospas-Sarsat
  Participants implement, maintain, co-ordinate and
  operate a satellite system capable of detecting
  distress alert transmissions from radiobeacons
  that comply with Cospas-Sarsat specifications and
  performance standards, and of determining their
  position anywhere on the globe. The distress
  alert and location data is provided by
  Cospas-Sarsat Participants to the responsible SAR
  services.
• Cospas-Sarsat co-operates with the International
  Civil Aviation Organization, the International
  Maritime Organization, the International
  Telecommunication Union and other international
  organisations to ensure the compatibility of the
  Cospas-Sarsat distress alerting services with the
  needs, the standards and the applicable
  recommendations of the international community.

13
Satellite Orbits - LEOSARs

• Low Earth Orbit (600km)
• 121.5, 243, 406 MHz
• Location by Doppler Effect
• 1 orbit around Earth takes about 90 minutes
• Oldest ELT satellite detection system

14
COSPAS vs SARSAT LEOSARs

• COSPAS
• Russian Equivalent to SARSAT
• Presently only 1 functional (COSPAS-9) satellite
  monitoring 121.5 MHz
• This system was never meant to monitor 243 or 406
  MHz

• SARSAT
• Search and Rescue Satellites
• 3 Fully Functional 121.5, 243, 406 monitoring
  satellites
• 2 Partially Functional

15
Doppler Effect

• LEOSARs use the Doppler Effect
• 1 Satellite Pass results in two possible
  locations
• 2 Satellite Passes eliminate the ghost location

16
Satellite Orbits - GEOSARs

• Geostationary Orbits
• 1 orbit 1 day
• Same spot in the sky
• 36,000km
• Monitor 406 MHz only
• Determines position with help of LEOSARs or if
  ELT encodes its position (GPS installed)

17
Notification

• No matter what satellite detects the signal,
  activation is the same
• COSPAS-SARSAT gt MCC gt RCC gt SAR

18
Weve been notified!

• Are the SARSAT coordinates exact?

19
SARSAT Coordinates are not Precise

• 121.5 MHz ELT data is accurate to about 12 miles
• A circle of radius 12 miles covers an area of 450
  square miles!
• 406 MHz ELT data is accurate to about 3 miles
• A circle of radius 3 miles covers an area of 28
  square miles!

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12 mile vs 3 mile radius
21
SARSAT gets us close

• Now what?
• How do we get closer?

22
The Old Little L-Per
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The Old Little L-Per

• LH-10
• 121 MHz aircraft range
• Will not pick up 243 MHz
• LH-16
• LH-10 243 MHz receiver

• The Standard in ELT Direction Finding
• Since 1974 L-Tronics has sold over 18,000 L-Pers
• www.ltronics.com

24
Controls

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

25
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

26
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)

27
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

28
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

29
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 arms
  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

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If you cant hear it

• If you cant 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 dont believe your L-Per
  readings

31
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 somethings up!

32
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

33
REC Mode

• The meter is tell 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)

34
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

35
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 youve followed this procedure, the highest
  reading youll see is mid-scale, everything else
  will be less than that
• At the highest meter reading, take a heading

36
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

37
DF Mode

• Always turn in the direction the needle points
• If the needle points right, turn right
• If the needle points left, turn left

38
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 its in front of
  or behind you

39
DF Mode

• To check 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

40
What if

• You get more than 1 direction you feel the ELT is
  coming from?
• You can hear the ELT but cant get the L-Per to
  tell you a good heading?
• REC and DF mode dont agree?

41
Then try

• Double check your instrument settings
• Have someone else double check your instrument
  settings
• Try a different location
• You dont have to move far (sometimes)
• Radio waves at 121.5 MHz have a wavelength of
  about 8 feet

42
ELT Polarization

• Polarization refers to the orientation of the
  electromagnetic waves as they radiate from the
  antenna relative to the earth
• Polarization mismatch can cause a 20 dB
  degradation in received signal strength
• That means if the polarization is incorrect on
  the L-Per the received signal could be 100 TIMES
  WEAKER!!

43
No mismatch
44
20 dB Mismatch
45
Comparison
46
How to check Polarization

• If youre not picking up the signal at all, try
  dipping the antennas horizontal to the ground
• If the signal appears change L-Per polarization
• If you are picking up the signal switch to REC
  mode, dip the antenna and see if the signal
  strength increases. Adjust sensitivity
  accordingly
• If the signal strength increases, change L-Per
  polarization

47
Can you find something you cant hear?

48
That depends

• If you cant 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 cant hear the ELTs
  swept tone, you shouldnt trust the L-Pers
  reading

49
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

50
Is the ELT broke or not there?

• We need to determine whether the ELT is
  malfunctioning or if there is really no signal
  present

51
Think the situation through

• Have you heard the ELT before?
• YES
• How long has it been since you last heard it?
• Did it sound OK then?
• NO
• You may be too far from the ELT
• Do the following check to look for a faulty ELT

52
Broke or not there?

• If the ELT is malfunctioning, it may be
  transmitting but without the swept tone
• There could be no audio tone whatsoever
• The tone could be continuous
• The tone could be random

53
When broke

• There should be a unique sound to the noise and
  reception on the ELT frequency
• The noise should sound different between your ELT
  frequency (121.5 for example) and the frequencies
  the ELT is not on (ex. 121.6, 121.775)

54
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

55
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

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How do you take a compass reading?

57
Compass Heading

• Once you determine what direction the ELT signal
  originates from
• Take a compass heading
• Record the information in the ground team log
• Radio the information back to base
• Plot the heading on a map

58
Compass Heading

• Some L-Pers have a compass built into the mast
• Most do not and 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

59
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

60
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

61
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

62
Old Little L-Per Tips n Tricks

• The unit runs on two 9v batteries only 1 is
  needed for operation

63
The Future of ELTs

• Changes are in progress!

64
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

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The New Little L-Per
66
The New Little L-Per
67
The New Little L-Per
68
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!

69
The New Little L-Per

• The Old Little L-Per has not been available new
  for some time
• New purchases will likely be toward the New
  Little L-Per
• Production started earlier this year
• Current price 750