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

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

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

4. 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

5. 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

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

7. ELT Basics: The Output
MHz
Continuous Transmission
Swept Tone

8. The Old Little L-Per

9. 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

10. 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

11. 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)

12. 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

13. 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

14. 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

15. 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

16. 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!

17. 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

18. 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

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

20. 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…

21. 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

22. 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)

23. 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

24. 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

25. 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?

26. 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 MHz have a wavelength of about 8 feet

27. 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

28. 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

29. 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

30. 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

31. How do you take a compass reading?

32. 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

33. 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

34. 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

35. 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

36. 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

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

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

39. Future of ELTs
COSPAS-SARSAT will no longer monitor 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 and/or 243 MHz for local homing

40. The New Little L-Per

41. The New Little L-Per

42. The New Little L-Per

43. 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!
MHz and MHz standard
It floats!

44. 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