LL Series Little L-Per®

Portable Direction Finder

OPERATING MANUAL

L-TRONICS®, Santa Barbara, Californiawww.ltronics.com

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Table of Contents

Introduction ....................................... 3Details on the Operating Screen (Display) ........................... 4Assembly for Operation .................... 5Summary of Operating Modes .......... 5Details on Operation ......................... 6 Operation in the DF Mode.............. 7 Operation in the Receive Mode ..... 7 Calibration...................................... 7 Changing Frequency...................... 8 Storing a Frequency....................... 9Using External Antennas .................. 9Other Adjustable Values ................... 9SET1 ................................................. 9External Power and Audio ................10Odds and Ends .................................10More About Batteries ........................11Direction Finding Techniques ...........13Determining Bearing Reliability.........13 Reliability Circle .............................13 Walking a Baseline ........................13Radio Signal Propagation .................13

Reflectors ......................................... 14 Reflectors Near the Transmitter .... 14 Reflections Near the Receiver ....... 14Blocked Signal, Single Reflector ...... 14 Blocked Signal, Multiple Reflectors14 Resolving Multiple Reflections....... 14Direction Finding Inside a Building ... 15Using the L-Per® in the Fore/Aft Mode............................... 15Horizontal Polarization...................... 15

List of Figures

Figure 1. Display Screen Condition Indicators...................... 4Figure 2. Operating Position for all Frequencies ........................ 5Figure 3. L-Per® Operating Screen in the DF Mode................. 6Figure 4. L-Per® Operating Screen in the Receive Mode ........ 6

Specifications

Battery operated double conversion superhetrodyne receiver with built-in tunable active an-tennas.

Frequency range 108 - 173.9999 and 215 - 269.9999 MHz. First IF 21.4 MHz. Second IF 455 kHz. Acceptance bandwidth 7 kHz. Image and spurious rejection >60 dB. Operating temperature range -20 to +60 C. Frequency stability @25 C <±5 ppm, full temp <±20 ppm. Selectable FM or logarithmic AM detection. Sensitivity at BNC jacks <-123 dBm for 12 dB SINAD FM, 6 dB s/n AM. Minimum trackable CW signal, left/right display <-132 dBm; receive mode with BFO <-140

dBm. Max signal for left/right DF >+5 dBm. Power 6 AA batteries or external 6-28VDC. Current 45 mA lights off, low volume, 85 mA lights on, 150 mA lights on and full volume. Typical alkaline battery life 30 hours Audio output 0.3W, 8 ohms. Weight with batteries 29 oz.

Indicates areas of latest revisions.

Copyright 2006 and 2008 by L-Tronics®, 5546 Cathedral Oaks Rd., Santa Barbara, CA 93111.www.ltronics.com. All rights reserved.

March 2008

LL Series Little L-Per® Portable Direction Finder

OPERATING MANUAL

INTRODUCTION

The LL Series portable direction fia compact, hand-held, synthesized rewith tunable, folding antennas capareceiving AM and FM signals. The case is high-impact plastic and all exmetal is stainless steel for corrosiontance. A finger-operated, gasketed plows the AA batteries to be quickly repExternal antenna jacks allow for connof L-Tronics® magnetic, flexible, and antennas, as well as other antennaas beams. A third connector on topreceiver can be used for external powearphones.

AN OPERATING INSTRUCTION MARY IS PRINTED ON THE LEFTOF THE FRONT PANEL. PLEASE RTO IT FREQUENTLY UNTIL YOUCOME FAMILIAR WITH THE EQUIPAND ITS OPERATION.

The DF display shows direction anal strength simultaneously, alongother information as shown in figure 1the display and the keyboard can benight use.

The receiver is pre-programme121.5 MHz in Channel 1, 243.0 MChannel 2, 121.775 MHz in ChannelMarine calling frequency 156.8 MChannel 4. These frequencies can

For those of you whan exception and rethat long or hard. If tales from friends ansympathy from us.

Attention!!

o “Don’t do manuals,” please makead this one at least once. It’s notyou prefer to guess or believe fairyd then screw it up, you will get little

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nder isceiverble ofsealedposed resis-lug al-laced.ection

aircrafts such of theer and

SUM- SIDEEFER BE-

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nd sig- with. Both lit for

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3, andHz in

not be

changed by the customer. Six additionalmemories can be programmed by user fromthe keyboard.

Direction finding techniques are thesame with this equipment as they are withthe older style LH Series Little L-Per®.There are some important differences in theoperation of this equipment. With the LL Se-ries:

1. It is not necessary to change anten-nas when changing frequencies.

2. The display shows left-right homingand signal strength (by number andscale) simultaneously.

3. The receiver is programmable onany frequency from 108 MHz to 174MHz and 215 MHz to 270 MHz.

4. The antenna system needs to becalibrated periodically with the CALkey (see instructions).

5. The unit is not field repairable inter-nally; breaking the security sealsbetween the case halves will voidthe warranty.

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DETAILS ON THE OPERATING SCREEN (DISPLAY)

DFin

1.

2.

3.

4.

1

2

3

4

5

Figure 1 shows mode illustratin

dicators.

Lock symbol. Inlocked

External Power.running on exter

Entry mode. Shofor frequency enfor a memory nu

Function indicatnate key definiti

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Figure 1. Dis

the operating scrg the various co

dicates most keys

Indicates that thenal power.ws “FR” when watry or “ST” when wmber for storage.or for selection of ons

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play Screen Condition Indicators

een inndition

are

DF is

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alter-

5. Battery condition6. Signal strength 7. Attenuation flag8. Receiving frequ9. Channel name o10. Secondary settin11. Signal strength

per dB12. Condition messa13. Fore/Aft DF bar14. Left/Right DF ba15. External antenn

13

barbarsency in r memogs (am

number

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ra indica

14

15

8 7

9

MHzry number/fm, lights etc.), about 3 counts

tor

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ASSEMBLY FOR OPERATION

The receiver is shipped with a protectivefilm covering the display. Carefully peel thisfilm off before use.

The receiver is also shipped with six AAalkaline batteries installed. Details on bat-tery requirements and installation are de-scribed in the section “More About Batter-ies” on page 11.

Unfold the antenna blades and handle byholding the receiver body with one handwhile unfolding the four antenna blades andthen the handle to their operating positions.Return them to the stored position in re-verse order (handle then blades).

For optimum DF accuracy set the an-tenna blades in the 90º position, as shownin Figure 2, for ALL frequencies. TheySHOULD NOT be fanned or set to the 120º.

Previous instructions had users fan theantenna to this 120º position when operat-ing in the VHF band; however it has beendetermined that DF errors can occur in thisconfiguration.

ALWAYS set the antenna blades asshown in Figure 2.

Figure 2. Operating Position for allFrequencies.

To turn the receiver on, hold the PWRkey down for 2-3 seconds. It will beep andthe display will come on. To turn the DF off,hold the PWR key down for one second. Itwill store the frequency and display settingscurrently being used, “beep,” print “OFF” onthe screen, and shut down when the key isreleased. Occasionally, the display does notfully erase; to clear, press the REC/DF but-ton twice.

The panel light key cycles between threestages: 1) display and keyboard lit; 2) dis-play only lit (brighter), and 3) Off. Using thelights add about 50% to average batterydrain. The letter “L” appears in the secon-dary settings area of the display to indicatethe lights are on in daylight (see Figure 1).

Whenever the receiver is operating, theup and down arrow keys raise or lower thespeaker volume. While programming, theyadjust frequency, contrast, and other func-tions. Continuous running at maximum vol-ume can cut battery life in half.

To use the DF, antennas are extendedand positioned as described above and thereceiver is held with the arm extended andthe display screen at or above eye level.This is VERY important for best DF accu-racy, as described later. This position iscalled the “operating position” and shown inFigure 2.

SUMMARY OF OPERATING MODES

There are three operating modes: 1. Left-right direction finding or homing; 2. Receive or signal strength; and 3. Fore-Aft/Left-Right (FALR) when

used with external antennas.

The DF and Receive modes are selectedby toggling the REC/DF pad on the key-board. In the Receive mode, the cross dis-appears and the word RECEIVE replaces iton the screen. The FALR mode is automati-cally selected when antennas are con-nected to both jacks on top of the receiver.

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In the DF mode, the antenna is rapidlyswitched, first to the left and then the right.The strength of the signal while pointing leftis subtracted from the strength while point-ing right and the result is shown by a dark-ening on the horizontal bar on the display toshow the direction of strongest signal. Thus,if the signal source is to the right of the DF,the bar will darken the pointer to the right.Turn in the direction the bar indicates until itnearly disappears or points equally left andright. The operator is now facing the signalsource. Any further turn in the same direc-tion (right) and the bar will darken to the op-posite side (left). Return to the centered in-dication to face the signal source. A “buzz”heard in the DF mode is normal.

In DF mode, the larger of left and rightsignals is selected for signal strength indi-cation. This makes the strength readingnearly independent of antenna angle (omni-directional). DF mode should be used forthe signal strength or build and fade methodof transmitter location,

Figure 3 shows the operating screen inDF mode with the various condition indica-tors.

Figure 3. L-Per® Operating Screen in theDF Mode.

In the Receive mode, the antennas actas a directional beam that is most sensitiveoff the left end of the receiver. In this mode,selected by the REC/DF key, the receivedsignal will have the greatest strength whenthe left end of the receiver front panel ispointed at the source. This maximum signalis rather broad but may be useful when onlya general direction is needed.

The DF will show one or more minimumamplitude points, often called nulls, butthese change depending on tuning and

should not be used for determining direc-tion. This mode also eliminates the “buzz”present in the DF mode and makes speecheasier to understand. A numerical indicationsupplements the vertical bar to indicate sig-nal strength, with about 400 being theweakest signal and about 850 the strongest.

Figure 4. L-Per® Operating Screen in theReceive Mode.

Details on operating in both the DF andReceive modes are covered in the DirectionFinding Techniques section (page 13).

When a vehicle is equipped with two setsof L-Tronics® DF antennas, one mountedfore-aft and the second left-right, the coaxleads are connected to the appropriate BNCjacks on top of the receiver. The display onthe DF then allows the fore/aft and left/rightbars to be displayed simultaneously to givea continuous “all around” indication in theDF mode.

DETAILS ON OPERATION

DF receivers intended for operation inthe United States have three standardemergency frequencies and one practicefrequency pre-programmed in the memory:

1. 121.500 ELT-1 AM2. 243.000 ELT-2 AM3. 121.775 TRAINING AM4 156.800 MARINE FM

Some receivers built for export and spe-cial operations may be programmed differ-ently.

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These settings are not changeable fromthe keyboard. If the DF ever gets into anunknown or unusable state, pressing one ofthese keys will reset to factory program-ming. These stored setups are often allthat’s needed for successful ELT andEPIRB location.

When the DF is turned on, it alwaysstarts with the setup it had when it was lastshut off. If this is not what is wanted, pressany key 0 - 9 to bring up either one of thepermanent setups or one that has beenstored earlier. If a blank memory is selected,an “EMPTY” message will appear brieflyand the setup will not change.

Operation in the DF Mode

To determine direction with best accu-racy, select the DF mode with the “REC/DF”key (the cross on the right half of the displayscreen will appear). Hold the unit by thehandle in the operating position: the screen(display) facing the operator and at eyelevel or higher with the antennas vertical asshown in Figure 2. Turn in the direction ofthe longer horizontal bar until the bar isshort and any remaining length is centeredin the cross display (display centered). Theoperator is now facing the signal source.Any further turn in the same direction willcause the bar to reverse. Always turn in thedirection indicated by the horizontal bar untilit is centered and any further turn will causeit to go to the opposite side.

Summary:

1. Select DF mode2. Hold unit with display facing youand at eye level (operating position)3. Turn in the direction of the longerhorizontal bar until the bar is short andcentered

Please read the above paragraph andsummary again. It is the most importantinformation in this instruction manual.With a small antenna and short handle, theoperator’s body is part of the antenna. Poorquality DF readings are guaranteed if theDF is held down by the operator’s beltbuckle, the antenna blades nearly touch the

operator’s arm, or curious onlookers gatherclose by.

Operation in the Receive Mode

Direction can also be found using Re-ceive mode. Press the “REC/DF” key. Thedirection cross on the display will be re-placed with the word “RECEIVE.” Hold theDF unit in the operating position as de-scribed above and turn to where thestrength bar is tallest or the strength numberis largest. The signal source is now off theleft end of the display as noted by the ar-rows on the panel. This mode is less pre-cise than DF mode but may be less affectedby severe reflections. The operator shouldknow how to use both modes.

The logarithmic strength display accu-rately shows changes of signal strength, butit was not calibrated for absolute level forsoftware below version 1.68. The same sig-nal may produce readings on different LLSeries DF receivers that vary by 10 dB or30 counts. If, in special circumstances, mul-tiple teams need to compare strength tobetter accuracy than this, a correction num-ber will need to be determined for each re-ceiver. The variance should be less than 10counts for later units.

Calibration.

The DF receiver employs both a trackingpre-selector and tuned active antennas togive good wide-range performance in asmall package. These circuits can changewith temperature and time and the antennasare sensitive to nearby objects like handsand arms or onlookers crowding about, par-ticularly when operating around 120 MHz.To correct potential errors, the calibrationcircuitry injects a known signal into the built-in antennas and “peaks up” the various cir-cuits.

Because the antennas are being adjustedfor hand held use, they MUST be unfoldedand the unit MUST be held in its operatingposition during calibration.

To calibrate, first select the desired oper-ating frequency and then press the “CAL”key. The display will show “HOLD” for threeseconds while the DF is moved to the oper-ating position. It will show "CAL” while the

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actual tuning takes place, and then “GOOD”if all is well. It is normal for the speaker tomake a noise and for the display to “jumparound” during calibration. If “FAIL” ap-pears, see below.

It is NOT necessary to calibrate the DFeach time it is used. It should NOT be cali-brated within 100 ft of an ELT or at a busycommunications site because this couldcause errors or false "FAIL" indication. Themost recent calibration values are stored inthe corresponding memory.

Calibration with an external antenna con-nected tunes up only the receiver. Settingsfor the built-in antennas are retained. If theDF has been calibrated for hand-held use,re-calibration for external antennas is un-necessary.

Calibration should be done any time a newfrequency is programmed, if the DF is heldin a different way, if the temperaturechanges by more than 40° F (20° C) or if ithas been more than six months since theequipment has been used. Calibration in aquiet radio RF environment will give thebest accuracy. Excessive calibration isn’tdamaging, just unnecessary.

If the DF is being used with external an-tennas, such as the L-Tronics® LVA seriesmagnetic antennas, only the receiver will becalibrated so the built-in antennas may beleft folded. Calibrating while hand-held alsocalibrates for vehicle use.

If calibration shows “FAIL”:1. Try again. There may have been

momentary outside interference.2. Make sure the antennas are set to

“AUTO” (SET1, item 2).3. Continue use. The old values are put

back after a CAL failure.4. Hold the DF with the body clear of the

antennas in the operating position asshown in Figure 2 and try again.

5. Fold and unfold antennas to clean thejoints.

6. Check the battery indicator. Replacebatteries if no bar is showing.

7. The receiver may not calibrate prop-erly above 162 MHz on units withsoftware revisions below 1.71 unlessthey have been upgraded

8. It may be too hot or cold. Tempera-ture limits are -10 to +140°F (-24 to60°C).

9. The DF may have failed. Contact thefactory for repair.

Changing Frequency

The receiving frequency may bechanged either by direct entry of the desiredfrequency or up or down in 100 Hz steps.

To change frequency, first, press the “F”key and the press “FREQ.” If the “FREQ”key is not pressed within five seconds, the“F” or alternate function condition resets. Ifthis happens, push “F” and then “FREQ”again. While in the frequency setting mode,the letters “FR” appear along the left edgeof the display. Press “F” to end frequencyentry.

To tune in a signal better, to discriminateagainst interference, or otherwise changethe frequency in small steps, press the up ordown arrow key. A short press will move byone step; holding the key down will causethe frequency to move up or down continu-ously. Any frequency, whether from opera-tor entry or from permanent memory, can bechanged this way. The changes will be keptwhen the DF is turned off and back on againbut they will not affect the values stored inmemory. Changing frequency in this waydoes NOT require a new calibration. Forexample, 121.5000 MHz loaded from mem-ory 1 could be changed with the arrows to121.5053 and stay there even if the DF wasturned off and on. Pressing 1 again wouldreturn to 121.5000.

A new frequency can be entered directlyby pressing “F” then “FREQ” and the de-sired frequency on the number keys. Onlythe significant digits need be entered andthe decimal point is automatic. Any missingdigits will be set to 0. Press “F” again tocomplete the entry. If the new frequency isout of range, “RANGE” will be displayedbriefly and the old frequency will remain un-changed. For example: the sequence “F, 1,3, 6, 2, F” would result in a frequency of136.2000 MHz. “F, 2, 6, F” would cause a“RANGE” error and retain the old frequency.CAL is required when a new frequency isentered this way.

Note that once an arrow key is pressed,direct entry is disabled and once entry isstarted, the arrows are disabled. If a mis

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take is made, just press “F” to quit and then“F” and “FREQ” again to start over.

Storing a frequency

After a new frequency is entered, it willbe labeled as “NEW” on the display. Thereis no provision for custom labels. This newfrequency will be retained if the power isturned off and back on but will be lost if anyother memory is loaded. To store this fre-quency for later use, press “F” then“STORE”. The letters “ST” will appear onthe left edge of the display. Select a mem-ory number for storage of this new fre-quency and press a number from 5 to 0.The old data, if any, in that memory locationwill be erased. The “NEW” label will be re-placed by the memory number when thisentry is later recalled. An attempt to store toa permanent memory location (positions 1through 4) will be rejected.

USING EXTERNAL ANTENNAS

Two BNC jacks are located on the top ofthe DF for connecting external antennas.When set for AUTOmatic operation, anyantenna with a DC resistance of 500 ohmsor less at its connector will be detected bythe DF when it is plugged in. The DF willshut off its internal antennas and work fromthe external one(s). It will return to using itsinternal antennas when the external anten-nas are disconnected. See also section onCalibration.

The L-Tronics® magnetic, flexible, air-craft, and LH Series L-Per® handheld an-tennas will all be detected. Adding a 470ohm resistor to the L-Tronics® LHBM-1beam and LVA-1 monitor antennas will al-low automatic detection of them, pluggedinto either jack.

NEVER apply power or more than 10mW RF or any DC voltage to these jacks.External antennas can also be selectedmanually (see “Other Adjustable Values”below). The jack that the external antenna isplugged in to sets whether the DF displaysthe data left and right (left/right jack) or upand down (fore/aft jack). Plugging two an-tennas at once will switch to the FALR(Fore/Aft-Left/Right) display.

There are two potential hazards associ-ated with external antennas:

1. External antennas usually cover onlya narrow frequency range. Beyondtheir designed frequency, they can bewildly erroneous.

2. The DF will not use its internal anten-nas unless it is set to AUTO (SET1).

Be careful with external antennas to besure they are used within their limits. Forexample, our magnetic and aircraft anten-nas have a range of only 118 to 126 MHzand 235 to 260 MHz.

OTHER ADJUSTABLE VALUES

Several other settings are selectable be-side frequency, DF mode and volume.These are controlled through setup screens“SET1,” ”SET2,” and “SET3.” “SET3” con-tains only the model number, frequencies,and revision numbers.

To work with the SET menus, press “F”and then “SET1,” “SET2” or “SET3.” One ormore items on a menu can be changed in asingle session by selecting its item number.Except for contrast, these selections areretained in the individual frequency memo-ries. To end the session, press “F” again.

SET1 + KEY PAD ENTRY NUMBERS

1. Pressing this number alternately se-lects FM or AM audio detection. This selec-tion affects only what is heard on thespeaker. It does not affect DF operation.The default is AM below 137 MHz andabove 235 MHz and FM elsewhere.

2. Pressing this number selects “AUTO,”“F/A,” “L/R,” and “FALR” antenna switching.The default for permanent memories is“AUTO.” The other choices allow for manualselection when using external antennas thatdo not give sensing for automatic selection.This MUST BE SET to AUTO for the built-inantennas to work.

3. Press 3 and then use the up anddown arrows to adjust the display contrast.If the display is too light to read, hold the UParrow and, if it is all black, hold the DOWNarrow until the display appears. Contrast isstored in a common memory so the last

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adjustment made applies to all frequencymemories.

4. Pressing this number selects “FAST,”“MEDIUM,” and “SLOW” display filters.“MEDIUM” is the default and is usually bestfor hand-held operation. “FAST” is best forcatching short, pulsed signals. "MEDIUM"and “SLOW” can reduce the flutter causedby nearby objects while driving or for de-tecting very weak signals.

5. ELT signals are usually strings ofpulses sent at a varying rate to give thewarble sound. The transmitter is usually ononly 1/3 of the time to give better batterylife. Peak detection gives better perform-ance on these signals and is the default forthe programmed ELT frequencies. It maygive an erroneous left or right indication withno signal on some frequencies. For com-munication signals, turn peak detection off.

6. Display gain allows reducing the sen-sitivity of the DF indications when largerexternal antennas are used. The default is“high.” It may be set to the operator's taste.

7. Turns the BFO ON or OFF if this op-tion is available. The change occurs whenleaving the menu.

It is common to use different default set-tings for mobile and walking. Preferred set-ups can be stored in some of the usermemories to be recalled when needed with-out having to reprogram each time. It isbetter to store a setting with the dial lightsoff so they aren’t part of the memory anddon’t run the batteries down unnoticed dur-ing the day.

EXTERNAL POWER AND AUDIO

The 6-pin jack on top of the DF betweenthe BNC jacks provides for external powerinput and audio output. An optional matingconnector with a 4 wire, 6 foot cable isavailable from L-Tronics® as part number120014. The mating connector only isavailable from Digi-Key (www.digikey.com)as p/n HR8560ND (Hirose HR30-6P-6S);soldering small pins is required. Connec-tions are:

Pin Color Function1 Black Ground2 Red + input power3 White Audio out

4 Green Reserved5 Reserved6 Reserved

To connect the cable, align the white ar-rows on the connector halves and push onthe back of the plug. To remove, pull on thering on the front of the plug, NOT the body.If it comes apart hard, it is being done im-properly and it may break.

The input voltage should be between 6and 28V. Maximum current with lights onand loud audio is about 250mA. The unit willwithstand up to +80V and –40V withoutdamage, but will not operate until the volt-age returns to the working range. The ex-ternal power input draws about 10mA withthe DF shut off.

The audio output will drive headphonesor a small speaker connected between pins3 and 1 (white and black). Do not applyexternal power to this line. The output levelvaries with the DF volume control.

ODDS AND ENDS

Pressing “F” and “LOCK” will partly lockthe keys. When locked, only the “POWER,”“LIGHT,” “REC/DF” and “LOCK” keys work.To unlock, press “F” and “LOCK” again.

Starting with software revision 1.71(shown on the bottom line of SET3) dated12 October 2006, an Automatic Power Off(APO) function has been added. The APOwill turn the DF off if no keys are pressed foreither 15 or 60 minutes. This will preventdischarge of the batteries if an operator for-gets to turn the DF off or if it is accidentallyturned on. The APO does not shut the DFoff when the external power is plugged in.The APO may be set to 15 minutes, 60minutes, or off by using SET2 (F, SET2, 1,F.) This upgrade can be added at the fac-tory to earlier units.

The receiver has a few low-level spuri-ous responses, particularly at multiples of 4MHz (116, 120, 124 MHz, etc.) that willcause the DF display to go off center. Thesewill be over-ridden by all but threshold-levelactual signals.

This DF has a narrow bandwidth loga-rithmic receiver. This means that older,wide-band FM communications signals andAM signals with full modulation will sound

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distorted. This is not a receiver fault. It alsomeans that reception of older ELTs, whichhave wider frequency tolerances, may beimproved by tuning the DF receiver fre-quency by a small amount using the UP andDOWN arrow keys. Careful tuning may alsoallow separation of two simultaneous ELTs.

One or two attenuators are switched in toextend the strength measurement range forstrong signals. They make an audible “ping”when they change and may cause a jump instrength numbers. The attenuator dots showwhen they are in use (Figure 1).

Occasionally, the LCD display can be-come confused. If this happens, pressingthe DF/REC key twice or the sequence F,SET1, F should clear it. Also, the key padmay not respond properly to rapid keypushing. Slow and deliberate works best.

The low temperature operating limit is setby the LCD display, which responds veryslowly when cold. Contrast adjustmenthelps somewhat. Slow and deliberate worksbest.

The case of the DF is sealed with thebattery plug in place. It is designed to with-stand water immersion to 10 ft and altitudeto 15,000 ft. With batteries installed, it doesfloat. If it is moved to a different altitude foran extended period and the weather is dry,we suggest opening the battery plug brieflyto equalize pressure. The case seal is nothermetic; moisture can accumulate insideas a fog on the display due to “pumping” bydaily temperature changes. If this happens,or if water gets inside for any other reason,remove the battery plug and let the case dryout. The process can be speeded by puttingit in a warm place, but not over 120°F.

The case should have a gap of .010 -.015 at the seal. DO NOT tighten the casescrews further.

BREAKING THE SECURITY SEALSAND OPENING THE CASE WILL VOIDTHE WARRANTY.

The folding handle is removable to allowthe DF to be mounted another way. Thescrew has ¼-20 threads, the same as usedon most camera equipment and tripods.Take care not to loose the “wavy plates”that are a part of the index mechanism. L-Tronics® also has a simple drop-in bracket,p/n 120013, available to keep the unit inplace in a car or airplane.

The screws holding the built-in antennasare sealed with Locktite®. Should one everwork loose, a drop of Locktite®7, preferably290 grade (green) should be applied to holdit and to maintain the case seal.

If the battery plug is lost, stuffing crum-pled aluminum foil into the open hole maykeep the DF running until a new plug is ac-quired.

Starting with software revision 1.71(shown on the bottom line of SET3) dated12 October 2006, a Beat Frequency Oscil-lator (BFO) function has been added. TheBFO allows unmodulated (carrier only) sig-nals to be heard and can give a small im-provement in the ability to hear very weakELT signals. Direction can be determined byturning the DF for the loudest signal in RE-CEIVE mode, using either the built-in an-tennas or an external beam antenna. IM-PORTANT: Listening for changes in audiovolume works only for weak and noisy sig-nals. For stronger signals, the sound be-comes constant and strength changes areindicated by the strength bar and numbers.The pitch of the BFO sound may be ad-justed by changing the receive frequency.Press f, then FR. Use the arrows to tune upor down and F again to stop tuning. Thefrequency will return to its saved value thenext time that memory channel is selected.This is an advanced technique and shouldbe practiced and well understood beforebeing used on an actual search. This up-grade can be added at the factory to earlierunits with serial numbers above 30197.

MORE ABOUT BATTERIES

First, no matter the type, use fresh, goodquality batteries. Customer reports and ourown experience over many years suggestfar fewer problems with Eveready® andDuracell® than any other manufacturers.Saving a dollar only to have a battery jam inthe tube, go dead when needed, or dribblecaustic goo in the works is really foolish. Ifpossible, buy from a store that sells a lot ofbatteries and check the date codes so youget fresh ones.

The LL Series Direction Finder uses six1.5V AA size batteries. For normal service,we recommend alkaline batteries, as thesegive the best combination of service life,

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cost, and resistance to corrosion. New alka-line batteries will run the DF for about 30hours. When the bar on the battery indicatorsymbol on the front panel display disap-pears, about one hour of operating time re-mains.

If long storage life or extended operationbelow –10º is needed, use 1.5V Lithium-ironsulfide batteries (Eveready L91).

NEVER USE 3V LITHIUM BATTERIES.They will damage the receiver.

Use NiCd or NiMh rechargeable cellsonly if your DF is being used an hour ormore per day.

To change batteries, unscrew the batteryplug on the right side of the DF until it isloose, then gently pull it out. Insert the bat-teries with the positive (+) end first into thebattery tube. Reseat the plug and push ingently to engage the threads, then screwthe cap in until the “O” ring is in contact withthe case all the way around.

Alkaline cells have a capacity of about2600 mAH at 68° F and should give about30 hours of operation with average volumesettings and panel light use. The DF will op-erate at full accuracy down to 5.4V from thebattery or 0.9 volts per cell to extract the fullbattery energy. Cells lose about 5% of theirenergy per year at 68°F, more if hotter andabout 1% if kept in a refrigerator. Only about45% of the battery energy is available at -10°F. Battery seals usually last more than 5years if the cell is not discharged but bat-teries still should be taken out if the DF willbe stored for a long time. If the batteries docorrode, get them out if you can and cleanout the mess with a DRY bottle brush.NEVER use any liquid cleaner as it can leakinto the circuit boards. Battery tubes arefactory replaceable.

Carbon-zinc batteries, strangely oftencalled “heavy duty,” have a capacity ofabout 1500 mAH, have only about 30% ofthat at -10°F and have a higher self-

discharge rate than alkaline. These shouldbe considered only if alkaline batteries arenot available.

Oxyride batteries from Panasonic® arerelatively new at a small price premium, butare not a good choice for the DF. Their ini-tial voltage of 1.7V per cell is just safe forthe DF and they have more available en-ergy than standard alkaline cells for cam-eras and toys but less at the current drain oftypical of DF operation. Further, the lowtemperature performance is poor.

Nickel-Cadmium and Nickel-Metal hy-dride batteries are a good choice if the DF isbeing used often such as for training. NiCdcells up to 1000mAH and NiMh cells toabout 2000mAH are available. This is fineas long as they can be readily recharged.The big problem with these batteries is thatthey self-discharge rapidly, particularly athigh temperature, and this leakage usuallygets higher with use, particularly if simplechargers are used.

The leakage in NiMh batteries can go sohigh that your DF can be dead after a fewhours in a closed car in summer. If you douse these batteries, note that the battery baron the screen is set for alkaline batteriesand will not indicate full scale even with afully charged battery.

A new type of lithium battery using ironsulfide came to our attention after the DFpanels were printed. This one is an excep-tion to the “no lithium” restriction. Currently,the Eveready® L91 is the only one we knowto be available and costs $2.50 or moreeach. These batteries have three advan-tages: self discharge of 1% per year at 68°For 15 year shelf life; better than 80% capac-ity at -10°F; and about 20% greater energythan alkaline batteries when used in the DF.A set of batteries is also about 2 ounceslighter.

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DIRECTION FINDING TECHNIQUES

Following is a summary of Direction FindingTechniques. More information can be obtainedfrom our publications LHTM-1, “Air and GroundDirection Finding,” LHTM-2, “Locating Non-distress ELTs and EPIRBs,” and LHTM-3, “BasicELT Location Course.” All techniques used bythe LH Series Little L-Per® Direction Finders isapplicable to the LL Series.

A key to the efficiency of the L-Per® is itsability to evaluate the quality of the bearingsobtained. Beware of reflections; it is impossiblein a practical sense to obtain bearings fromsome locations. The L-Per® will tell you quicklywhen this situation exists so a new site can beselected. Further, bearings of low quality can beidentified and taken into account when conflictsoccur in a triangulation problem.

We strongly recommend that you do initialpractice with the DF in an open, clear area andthen around buildings or other obstructions tobecome familiar with its operation with a knowntarget before trying an unknown. A practice ELTfitted with a dummy load in place of its regularantenna will provide weak signal simulationpractice in walking range.

DETERMINING BEARING RELIABILITY

Reliability Circle

In the DF mode, turn in the direction the bar in-dicates until it nearly disappears or pointsequally left and right. You are facing the signalsource. Now slowly turn in a full circle to theright while holding the DF in the operating posi-

tion and watching the display. The bar shoulddarken to the left, center at approximately oppo-site the ELT, darken on the right side, then cen-ter when you are again facing the signal source.

If the bar centers twice, about 180 degreesapart, the location is good and the bearing willbe accurate. If it centers more than twice, ortwice but less than 120 degrees apart, it is not agood location and bearings won’t be accurate.Choose a better location for DF.

Walking a Baseline

After performing the reliability check as de-scribed above and finding a good location,check for the existence and severity of reflec-tions. You might, by good luck, have chosen aspot that may initially shows good bearing reli-ability but is really not.

In the DF mode, center the bar and walk astraight line for 10 to 20 feet WHILE CON-TINUOUSLY OBSERVING THE INDICATEDDIRECTION. If no significant reflections are pre-sent, the indicated direction will remain steady towithin five degrees.

As reflected signals become prominent, theindicated direction will oscillate back and forthevery four or five feet. A good estimate of thetrue direction of the signal can be made by tak-ing an “eyeball average” of these variationswhile walking a baseline of up to 50 feet. Fluc-tuations of more than 60 degrees each directionindicates a very poor DF site.

RADIO SIGNAL PROPAGATION

There are three characteristics of any radiosignal that MUST be understood to locate thetransmitter. They are:

1. Unimpeded, radio signals travel in a straightline. This principle is responsible for satel-lites being able to hear an ELT even thoughobjects on the ground prevent it from beingheard there.

2. Signals get stronger near the source. Thefurther away from the signal source, theweaker the signal is if it isn’t blocked. In ad-dition, the RATE OF CHANGE in signalstrength is faster as you get closer. Differentconditions can influence absolute signalstrength but usually don’t affect the rate ofchange. This makes rate of change a more

reliable indication of how close you are tothe transmitter than any given strengthreading.

3. Conductive objects reflect and/or block thesignal. These include metal structures,stucco buildings (chicken-wire mesh), con-crete buildings (steel reinforcing bars), chainlink fences, buildings with metalized glasssunscreens, mountains, smooth snowfields,and grasslands. These objects are called“reflectors” because they cause the trans-mitter’s signal to bounce off, much the sameway a mirror reflects images.

All DF techniques will come back to one ormore of these principles.

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REFLECTORS

Reflections cause almost off of the problemsin transmitter (ELT and EPIRB) location.

Solid conductive objects, like metal buildingsand mountains, both reflect and block the signal.Non-solid objects like fences will reflect some ofthe signal and allow most of it to pass through.Non-conductive objects act much the same wayas the metal fence. The L-Per®’s response de-pends on the reflector’s location. You’ll havedifferent results with a reflector near the trans-mitter, one near the receiver, and one betweenthe ELT and the L-Per®.

Reflectors Near The Transmitter

A reflector near the transmitter can affectyour ability to hear the signal, but usually causesno problem in tracking once the signal directfrom the transmitter can be heard.

If the ELT is next to a metal building, most ofthe signal will reflect or “bounce off” the buildingrather than go through it. The signal will be diffi-cult to hear and track when you are in a locationthat places the building between you and theELT. If you can hear the ELT, the L-Per® willgive good directional information because boththe direct and reflected signal are coming fromthe same direction.

Reflectors Near The Receiver

A reflector near the receiver can cause se-vere problems for the L-Per®, but once recog-nized, can usually be avoided.

A reflector within about 200 feet of the L-Per®

will cause it to see both the direct and reflectedsignal, but each will be from a different direction.However, the signal direct from the ELT will bestronger than a reflected signal and the L-Per®

will prefer the stronger, direct one.Reflected signals always lose power. They

will be weaker than the direct signal from theELT if – and this is the biggest if – nothing isblocking the direct signal.

Blocked Signal, Single Reflector

Reflections are not much of a problem in ELTlocation UNLESS the direct signal from the ELTis blocked. When blockage occurs, the directionfinder will “see” all of the reflections, which willvary in strength and direction.

In some cases where the signal is blocked,the solution to the problem is rather straightfor-ward. If the L-Per® hears a reflected signal fromonly one direction, it will track the reflection untilit can hear the direct signal. Once it does, direc-tion to the ELT will be obvious and it will giveyou a heading to the stronger, direct signal.

Blocked Signal, Multiple Reflectors

Multiple reflections coming from the samegeneral direction when the direct signal isblocked will cause much the same results as asingle reflector. The L-Per® will follow the reflec-tions until it hears the stronger, direct signal thenwill track the ELT.

As you walk while tracking the reflections,you may notice the apparent direction swingsback and forth, but you’ll be walking a line thatrepresents an average of the directions to thereflections.

Resolving Multiple Reflections

If your initial bearings on an airport ramp looklike you will be working among multiple reflec-tions, such as a group of hangars, you shouldexpect the L-Per® to have difficulty averagingdirectional information when among the build-ings. There are a couple of ways to recognizeand deal with this problem.

To evaluate the severity of reflections, makea 360-degree reliability turn while observing theDF display. If you get multiple centerings as youturn, you are in an area of reflectors. Next, walk15 or 20 feet and keep the bar centered bymoving the receiver back and forth. Take a step,swing the receiver to center the display, takeanother step, center the bar, take another step,center, etc. If you have to swing the receiver inan arc of more than 120 degrees, you have re-flections coming from all directions and the DFwill not be usable.

If your swings are less than 120 degrees, youcan continue walking in a direction that is anaverage of the headings of the swings. This isnot a precise method of DFing, but it will keepyou moving in the right direction.

When reflections are coming from many di-rections or all sides of the L-Per®, the combineddirectional information will be very confusing toit. The best procedure is to get out of the area.Move 200 feet or more away from the reflectorsand walk completely around them if possible.The L-Per® will give good directional informationfrom all sides, even though the direct signal maybe blocked from certain angles. This will giveyou a clearer picture of the area of highest prob-ability before you have to search among thebuildings. You can often isolate a single suspectbuilding from this “standoff” position.

Now you will have a better idea of where tostart your close-in search. DF mode may notwork in this area; if it doesn’t, use the “build andfade” method using the strength indications.Direction Finding Inside a Building

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Direction indications is often not useful insidea building because of so many reflections nearthe receiver. If there are a number of aircraftinside, it is often faster to rely only on strengthreadings. Strength response is not directional inDF mode. Use DF mode while walking about ahanger or rooms in a building, looking forchanges in strength reading. The Model LL L-Per® has enough strength range that offset tun-ing or external small antennas are unnecessary.

As you walk around the building, watch thestrength reading. Continue walking in the direc-tion that causes the strength to increase. Ignoresmall variations of strength five to 10 feet apart.

While you walk, look around for the ELT or alocation where it might be, such as a table,locker, flight bag, etc.

Using the L-Per® in the Fore/Aft Mode

When reflections are a real problem, such asamong metal buildings or in harbors, you canuse the L-Per® in the Fore/Aft mode, just as youwould on a vehicle.

Select the DF mode and then, instead of hoHolding the unit in front of you at eye level,

hold it off your right shoulder so you have to turnyour head to the right to see the display. The leftend of the DF (with the arrows) is facing forward.As you walk holding the receiver in this position,watch the left-right bar and keep the bar pointingto the left side. As long as the bar is on the leftside of center, you are walking toward the signalsource. If the bar is on the right side of center,you are walking away from the ELT.

Horizontal Polarization

The LL Series Direction Finder works bestwith transmitters that have vertically polarizedantennas. The most accurate bearings are ob-tained when the antennas on the transmitter andreceiver are the same polarization. If the ELT islying on its side and transmitting a signal that ishorizontally polarized, the result can act as abarrier in the direct path and emphasize the re-flections.

If holding the L-Per® horizontally overheadshows a strength increase of 20 counts or more,the signal is horizontally polarized. While notconvenient, the L-Per® can be held overhead ina horizontal position and worked in the “fore/aft”mode as just described.