L-Tronics Little L-Per LL Series User manual

LL Series Little L-Per®
Portable Direction Finder
OPERATING MANUAL

2
Table of Contents
Introduction ....................................... 3
Details on the Operating
Screen (Display) ........................... 4
Assembly for Operation .................... 5
Summary of Operating Modes .......... 5
Details on Operation ......................... 6
Operation in the DF Mode.............. 7
Operation in the Receive Mode ..... 7
Calibration...................................... 7
Changing Frequency...................... 8
Storing a Frequency....................... 9
Using External Antennas .................. 9
Other Adjustable Values ................... 9
SET1 ................................................. 9
External Power and Audio ................10
Odds and Ends .................................10
More About Batteries ........................11
Direction Finding Techniques ...........13
Determining Bearing Reliability.........13
Reliability Circle .............................13
Walking a Baseline ........................13
Radio Signal Propagation .................13
Reflectors ......................................... 14
Reflectors Near the Transmitter .... 14
Reflections Near the Receiver....... 14
Blocked Signal, Single Reflector ...... 14
Blocked Signal, Multiple Reflectors 14
Resolving Multiple Reflections....... 14
Direction Finding Inside a Building ... 15
Using the L-Per®in the
Fore/Aft Mode............................... 15
Horizontal Polarization...................... 15
List of Figures
Figure 1. Display Screen
Condition Indicators...................... 4
Figure 2. Operating Position
for all Frequencies ........................ 5
Figure 3. L-Per®Operating
Screen in the DF Mode................. 6
Figure 4. L-Per®Operating
Screen in the Receive Mode ........ 6
Specifications
¾Battery operated double conversion superhetrodyne receiver with built-in tunable active an-
tennas.
¾Frequency range 108 - 173.9999 and 215 - 269.9999 MHz.
¾First IF 21.4 MHz. Second IF 455 kHz.
¾Acceptance bandwidth 7 kHz.
¾Image and spurious rejection >60 dB.
¾Operating temperature range -20 to +60 C.
¾Frequency stability @25 C <±5 ppm, full temp <±20 ppm.
¾Selectable FM or logarithmic AM detection.
¾Sensitivity at BNC jacks <-123 dBm for 12 dB SINAD FM, 6 dB s/n AM.
¾Minimum trackable CW signal, left/right display <-132 dBm; receive mode with BFO <-140
dBm.
¾Max signal for left/right DF >+5 dBm.
¾Power 6 AA batteries or external 6-28VDC.
¾Current 45 mA lights off, low volume, 85 mA lights on, 150 mA lights on and full volume.
¾Typical alkaline battery life 30 hours
¾Audio 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

3
LL Series Little L-Per®Portable Direction Finder
OPERATING MANUAL
INTRODUCTION
The LL Series portable direction finder is
a compact, hand-held, synthesized receiver
with tunable, folding antennas capable of
receiving AM and FM signals. The sealed
case is high-impact plastic and all exposed
metal is stainless steel for corrosion resis-
tance. A finger-operated, gasketed plug al-
lows the AA batteries to be quickly replaced.
External antenna jacks allow for connection
of L-Tronics®magnetic, flexible, and aircraft
antennas, as well as other antennas such
as beams. A third connector on top of the
receiver can be used for external power and
earphones.
AN OPERATING INSTRUCTION SUM-
MARY IS PRINTED ON THE LEFT SIDE
OF THE FRONT PANEL. PLEASE REFER
TO IT FREQUENTLY UNTIL YOU BE-
COME FAMILIAR WITH THE EQUIPMENT
AND ITS OPERATION.
The DF display shows direction and sig-
nal strength simultaneously, along with
other information as shown in figure 1. Both
the display and the keyboard can be lit for
night use.
The receiver is pre-programmed with
121.5 MHz in Channel 1, 243.0 MHz in
Channel 2, 121.775 MHz in Channel 3, and
Marine calling frequency 156.8 MHz in
Channel 4. These frequencies cannot be
changed by the customer. Six additional
memories can be programmed by user from
the keyboard.
Direction finding techniques are the
same with this equipment as they are with
the older style LH Series Little L-Per®.
There are some important differences in the
operation 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 homing
and signal strength (by number and
scale) simultaneously.
3. The receiver is programmable on
any frequency from 108 MHz to 174
MHz and 215 MHz to 270 MHz.
4. The antenna system needs to be
calibrated periodically with the CAL
key (see instructions).
5. The unit is not field repairable inter-
nally; breaking the security seals
between the case halves will void
the warranty.
Attention!!
For those of you who “Don’t do manuals,” please make
an exception and read this one at least once. It’s not
that long or hard. If you prefer to guess or believe fairy
tales from friends and then screw it up, you will get little
sympathy from us.

4
DETAILS ON THE OPERATING SCREEN (DISPLAY)
Figure 1. Display Screen Condition Indicators
Figure 1 shows the operating screen in
DF mode illustrating the various condition
indicators.
1. Lock symbol. Indicates most keys are
locked
2. External Power. Indicates that the DF is
running on external power.
3. Entry mode. Shows “FR” when waiting
for frequency entry or “ST” when waiting
for a memory number for storage.
4. Function indicator for selection of alter-
nate key definitions
5. Battery condition bar
6. Signal strength bar
7. Attenuation flags
8. Receiving frequency in MHz
9. Channel name or memory number
10. Secondary settings (am/fm, lights etc.)
11. Signal strength number, about 3 counts
per dB
12. Condition messages
13. Fore/Aft DF bar
14. Left/Right DF bar
15. External antenna indicator
1
2
3
4
5
6
12
10
11
13
14
15
8
7
9

5
ASSEMBLY FOR OPERATION
The receiver is shipped with a protective
film covering the display. Carefully peel this
film off before use.
The receiver is also shipped with six AA
alkaline 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 by
holding the receiver body with one hand
while unfolding the four antenna blades and
then 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 shown
in Figure 2, for ALL frequencies. They
SHOULD NOT be fanned or set to the 120º.
Previous instructions had users fan the
antenna to this 120º position when operat-
ing in the VHF band; however it has been
determined that DF errors can occur in this
configuration.
ALWAYS set the antenna blades as
shown in Figure 2.
Figure 2. Operating Position for all
Frequencies.
To turn the receiver on, hold the PWR
key down for 2-3 seconds. It will beep and
the display will come on. To turn the DF off,
hold the PWR key down for one second. It
will store the frequency and display settings
currently being used, “beep,” print “OFF” on
the screen, and shut down when the key is
released. Occasionally, the display does not
fully erase; to clear, press the REC/DF but-
ton twice.
The panel light key cycles between three
stages: 1) display and keyboard lit; 2) dis-
play only lit (brighter), and 3) Off. Using the
lights add about 50% to average battery
drain. The letter “L” appears in the secon-
dary settings area of the display to indicate
the lights are on in daylight (see Figure 1).
Whenever the receiver is operating, the
up and down arrow keys raise or lower the
speaker volume. While programming, they
adjust frequency, contrast, and other func-
tions. Continuous running at maximum vol-
ume can cut battery life in half.
To use the DF, antennas are extended
and positioned as described above and the
receiver is held with the arm extended and
the display screen at or above eye level.
This is VERY important for best DF accu-
racy, as described later. This position is
called the “operating position” and shown in
Figure 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 selected
by toggling the REC/DF pad on the key-
board. In the Receive mode, the cross dis-
appears and the word RECEIVE replaces it
on the screen. The FALR mode is automati-
cally selected when antennas are con-
nected to both jacks on top of the receiver.

6
In the DF mode, the antenna is rapidly
switched, first to the left and then the right.
The strength of the signal while pointing left
is subtracted from the strength while point-
ing right and the result is shown by a dark-
ening on the horizontal bar on the display to
show 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 it
nearly disappears or points equally left and
right. The operator is now facing the signal
source. 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 right
signals is selected for signal strength indi-
cation. This makes the strength reading
nearly independent of antenna angle (omni-
directional). DF mode should be used for
the signal strength or build and fade method
of transmitter location,
Figure 3 shows the operating screen in
DF mode with the various condition indica-
tors.
Figure 3. L-Per®Operating Screen in the
DF Mode.
In the Receive mode, the antennas act
as a directional beam that is most sensitive
off the left end of the receiver. In this mode,
selected by the REC/DF key, the received
signal will have the greatest strength when
the left end of the receiver front panel is
pointed at the source. This maximum signal
is rather broad but may be useful when only
a general direction is needed.
The DF will show one or more minimum
amplitude points, often called nulls, but
these 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 speech
easier to understand. A numerical indication
supplements the vertical bar to indicate sig-
nal strength, with about 400 being the
weakest signal and about 850 the strongest.
Figure 4. L-Per®Operating Screen in the
Receive Mode.
Details on operating in both the DF and
Receive modes are covered in the Direction
Finding Techniques section (page 13).
When a vehicle is equipped with two sets
of L-Tronics®DF antennas, one mounted
fore-aft and the second left-right, the coax
leads are connected to the appropriate BNC
jacks on top of the receiver. The display on
the DF then allows the fore/aft and left/right
bars to be displayed simultaneously to give
a continuous “all around” indication in the
DF mode.
DETAILS ON OPERATION
DF receivers intended for operation in
the United States have three standard
emergency frequencies and one practice
frequency pre-programmed in the memory:
1. 121.500 ELT-1 AM
2. 243.000 ELT-2 AM
3. 121.775 TRAINING AM
4 156.800 MARINE FM
Some receivers built for export and spe-
cial operations may be programmed differ-
ently.

7
These settings are not changeable from
the keyboard. If the DF ever gets into an
unknown or unusable state, pressing one of
these keys will reset to factory program-
ming. These stored setups are often all
that’s needed for successful ELT and
EPIRB location.
When the DF is turned on, it always
starts with the setup it had when it was last
shut off. If this is not what is wanted, press
any key 0 - 9 to bring up either one of the
permanent setups or one that has been
stored earlier. If a blank memory is selected,
an “EMPTY” message will appear briefly
and 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 display
screen will appear). Hold the unit by the
handle in the operating position: the screen
(display) facing the operator and at eye
level or higher with the antennas vertical as
shown in Figure 2. Turn in the direction of
the longer horizontal bar until the bar is
short and any remaining length is centered
in the cross display (display centered). The
operator is now facing the signal source.
Any further turn in the same direction will
cause the bar to reverse. Always turn in the
direction indicated by the horizontal bar until
it is centered and any further turn will cause
it to go to the opposite side.
Summary:
1. Select DF mode
2. Hold unit with display facing you
and at eye level (operating position)
3. Turn in the direction of the longer
horizontal bar until the bar is short and
centered
Please read the above paragraph and
summary again. It is the most important
information in this instruction manual.
With a small antenna and short handle, the
operator’s body is part of the antenna. Poor
quality DF readings are guaranteed if the
DF is held down by the operator’s belt
buckle, the antenna blades nearly touch the
operator’s arm, or curious onlookers gather
close by.
Operation in the Receive Mode
Direction can also be found using Re-
ceive mode. Press the “REC/DF” key. The
direction cross on the display will be re-
placed with the word “RECEIVE.” Hold the
DF unit in the operating position as de-
scribed above and turn to where the
strength bar is tallest or the strength number
is largest. The signal source is now off the
left 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 affected
by severe reflections. The operator should
know how to use both modes.
The logarithmic strength display accu-
rately shows changes of signal strength, but
it was not calibrated for absolute level for
software below version 1.68. The same sig-
nal may produce readings on different LL
Series DF receivers that vary by 10 dB or
30 counts. If, in special circumstances, mul-
tiple teams need to compare strength to
better accuracy than this, a correction num-
ber will need to be determined for each re-
ceiver. The variance should be less than 10
counts for later units.
Calibration.
The DF receiver employs both a tracking
pre-selector and tuned active antennas to
give good wide-range performance in a
small package. These circuits can change
with temperature and time and the antennas
are sensitive to nearby objects like hands
and arms or onlookers crowding about, par-
ticularly when operating around 120 MHz.
To correct potential errors, the calibration
circuitry injects a known signal into the built-
in antennas and “peaks up” the various cir-
cuits.
Because the antennas are being adjusted
for hand held use, they MUST be unfolded
and the unit MUST be held in its operating
position during calibration.
To calibrate, first select the desired oper-
ating frequency and then press the “CAL”
key. The display will show “HOLD” for three
seconds while the DF is moved to the oper-
ating position. It will show "CAL” while the

8
actual tuning takes place, and then “GOOD”
if all is well. It is normal for the speaker to
make a noise and for the display to “jump
around” during calibration. If “FAIL” ap-
pears, see below.
It is NOT necessary to calibrate the DF
each time it is used. It should NOT be cali-
brated within 100 ft of an ELT or at a busy
communications site because this could
cause errors or false "FAIL" indication. The
most recent calibration values are stored in
the corresponding memory.
Calibration with an external antenna con-
nected tunes up only the receiver. Settings
for the built-in antennas are retained. If the
DF has been calibrated for hand-held use,
re-calibration for external antennas is un-
necessary.
Calibration should be done any time a new
frequency is programmed, if the DF is held
in a different way, if the temperature
changes by more than 40°F (20°C) or if it
has been more than six months since the
equipment has been used. Calibration in a
quiet radio RF environment will give the
best accuracy. Excessive calibration isn’t
damaging, just unnecessary.
If the DF is being used with external an-
tennas, such as the L-Tronics®LVA series
magnetic antennas, only the receiver will be
calibrated so the built-in antennas may be
left folded. Calibrating while hand-held also
calibrates 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 as
shown in Figure 2 and try again.
5. Fold and unfold antennas to clean the
joints.
6. Check the battery indicator. Replace
batteries if no bar is showing.
7. The receiver may not calibrate prop-
erly above 162 MHz on units with
software revisions below 1.71 unless
they have been upgraded
8. It may be too hot or cold. Tempera-
ture limits are -10 to +140°F (-24 to
60°C).
9. The DF may have failed. Contact the
factory for repair.
Changing Frequency
The receiving frequency may be
changed either by direct entry of the desired
frequency 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. If
this happens, push “F” and then “FREQ”
again. While in the frequency setting mode,
the letters “FR” appear along the left edge
of the display. Press “F” to end frequency
entry.
To tune in a signal better, to discriminate
against interference, or otherwise change
the frequency in small steps, press the up or
down arrow key. A short press will move by
one step; holding the key down will cause
the frequency to move up or down continu-
ously. Any frequency, whether from opera-
tor entry or from permanent memory, can be
changed this way. The changes will be kept
when the DF is turned off and back on again
but they will not affect the values stored in
memory. Changing frequency in this way
does NOT require a new calibration. For
example, 121.5000 MHz loaded from mem-
ory 1 could be changed with the arrows to
121.5053 and stay there even if the DF was
turned off and on. Pressing 1 again would
return to 121.5000.
A new frequency can be entered directly
by pressing “F” then “FREQ” and the de-
sired frequency on the number keys. Only
the significant digits need be entered and
the decimal point is automatic. Any missing
digits will be set to 0. Press “F” again to
complete the entry. If the new frequency is
out of range, “RANGE” will be displayed
briefly and the old frequency will remain un-
changed. For example: the sequence “F, 1,
3, 6, 2, F” would result in a frequency of
136.2000 MHz. “F, 2, 6, F” would cause a
“RANGE” error and retain the old frequency.
CAL is required when a new frequency is
entered this way.
Note that once an arrow key is pressed,
direct entry is disabled and once entry is
started, the arrows are disabled. If a mis

9
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 will
be labeled as “NEW” on the display. There
is no provision for custom labels. This new
frequency will be retained if the power is
turned off and back on but will be lost if any
other memory is loaded. To store this fre-
quency for later use, press “F” then
“STORE”. The letters “ST” will appear on
the 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 location
will be erased. The “NEW” label will be re-
placed by the memory number when this
entry is later recalled. An attempt to store to
a permanent memory location (positions 1
through 4) will be rejected.
USING EXTERNAL ANTENNAS
Two BNC jacks are located on the top of
the DF for connecting external antennas.
When set for AUTOmatic operation, any
antenna with a DC resistance of 500 ohms
or less at its connector will be detected by
the DF when it is plugged in. The DF will
shut off its internal antennas and work from
the external one(s). It will return to using its
internal antennas when the external anten-
nas are disconnected. See also section on
Calibration.
The L-Tronics®magnetic, flexible, air-
craft, and LH Series L-Per®handheld an-
tennas will all be detected. Adding a 470
ohm resistor to the L-Tronics®LHBM-1
beam and LVA-1 monitor antennas will al-
low automatic detection of them, plugged
into either jack.
NEVER apply power or more than 10
mW RF or any DC voltage to these jacks.
External antennas can also be selected
manually (see “Other Adjustable Values”
below). The jack that the external antenna is
plugged in to sets whether the DF displays
the data left and right (left/right jack) or up
and 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 only
a narrow frequency range. Beyond
their designed frequency, they can be
wildly erroneous.
2. The DF will not use its internal anten-
nas unless it is set to AUTO (SET1).
Be careful with external antennas to be
sure they are used within their limits. For
example, our magnetic and aircraft anten-
nas have a range of only 118 to 126 MHz
and 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 or
more items on a menu can be changed in a
single session by selecting its item number.
Except for contrast, these selections are
retained 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 the
speaker. It does not affect DF operation.
The default is AM below 137 MHz and
above 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 manual
selection when using external antennas that
do not give sensing for automatic selection.
This MUST BE SET to AUTO for the built-in
antennas to work.
3. Press 3 and then use the up and
down arrows to adjust the display contrast.
If the display is too light to read, hold the UP
arrow and, if it is all black, hold the DOWN
arrow until the display appears. Contrast is
stored in a common memory so the last

10
adjustment made applies to all frequency
memories.
4. Pressing this number selects “FAST,”
“MEDIUM,” and “SLOW” display filters.
“MEDIUM” is the default and is usually best
for hand-held operation. “FAST” is best for
catching short, pulsed signals. "MEDIUM"
and “SLOW” can reduce the flutter caused
by nearby objects while driving or for de-
tecting very weak signals.
5. ELT signals are usually strings of
pulses sent at a varying rate to give the
warble sound. The transmitter is usually on
only 1/3 of the time to give better battery
life. Peak detection gives better perform-
ance on these signals and is the default for
the programmed ELT frequencies. It may
give an erroneous left or right indication with
no 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 larger
external 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 when
leaving 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 user
memories to be recalled when needed with-
out having to reprogram each time. It is
better to store a setting with the dial lights
off so they aren’t part of the memory and
don’t run the batteries down unnoticed dur-
ing the day.
EXTERNAL POWER AND AUDIO
The 6-pin jack on top of the DF between
the BNC jacks provides for external power
input and audio output. An optional mating
connector with a 4 wire, 6 foot cable is
available from L-Tronics®as part number
120014. The mating connector only is
available from Digi-Key (www.digikey.com)
as p/n HR8560ND (Hirose HR30-6P-6S);
soldering small pins is required. Connec-
tions are:
Pin Color Function
1 Black Ground
2 Red + input power
3 White Audio out
4 Green Reserved
5 Reserved
6 Reserved
To connect the cable, align the white ar-
rows on the connector halves and push on
the back of the plug. To remove, pull on the
ring 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 6
and 28V. Maximum current with lights on
and loud audio is about 250mA. The unit will
withstand up to +80V and –40V without
damage, but will not operate until the volt-
age returns to the working range. The ex-
ternal power input draws about 10mA with
the DF shut off.
The audio output will drive headphones
or a small speaker connected between pins
3 and 1 (white and black). Do not apply
external power to this line. The output level
varies with the DF volume control.
ODDS AND ENDS
Pressing “F” and “LOCK” will partly lock
the 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) dated
12 October 2006, an Automatic Power Off
(APO) function has been added. The APO
will turn the DF off if no keys are pressed for
either 15 or 60 minutes. This will prevent
discharge of the batteries if an operator for-
gets to turn the DF off or if it is accidentally
turned on. The APO does not shut the DF
off when the external power is plugged in.
The APO may be set to 15 minutes, 60
minutes, 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 4
MHz (116, 120, 124 MHz, etc.) that will
cause the DF display to go off center. These
will be over-ridden by all but threshold-level
actual signals.
This DF has a narrow bandwidth loga-
rithmic receiver. This means that older,
wide-band FM communications signals and
AM signals with full modulation will sound