Lectrosonics LMAM, LMAL Users Manual
LMa
Frequency-Agile UHF Belt-Pack Transmitter
INSTRUCTION MANUAL
Featuring
Digital Hybrid Wireless™ Technology
(US Patent Pending)
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Purchase Date:
Rio Rancho, NM, USA
www.lectrosonics.com
LM/IM
Table of Contents
Introduction .............................................................................................................................................................................................4
Digital Hybrid Technology ................................................................................................................................................................. 4
Frequency Agility ............................................................................................................................................................................... 4
Wide-Band Deviation .........................................................................................................................................................................4
Long Battery Life ...............................................................................................................................................................................4
Servo Input ........................................................................................................................................................................................5
Input Limiter .......................................................................................................................................................................................5
No Pre-Emphasis/De-Emphasis ........................................................................................................................................................5
Pilot Tone Squelch .............................................................................................................................................................................5
Antenna .............................................................................................................................................................................................5
LMa Block Diagram ...........................................................................................................................................................................5
Controls and Functions
Input Jack ..........................................................................................................................................................................................6
Power ON/OFF Switch ......................................................................................................................................................................6
Power LED ........................................................................................................................................................................................6
Frequency Select Switches ...............................................................................................................................................................6
Modulation LEDs ...............................................................................................................................................................................6
Audio Level ........................................................................................................................................................................................6
Antenna .............................................................................................................................................................................................6
Belt Clip .............................................................................................................................................................................................6
Battery Installation .............................................................................................................................................................................7
Operating Instructions
Selecting the Compatibility Mode ......................................................................................................................................................8
Attaching a Microphone or Musical Instrument and Adjusting Audio Levels ..................................................................................... 8
Adjusting the Transmitter Frequency ................................................................................................................................................. 9
5-Pin Input Jack Wiring
Microphone RF Bypassing ..............................................................................................................................................................10
Line Level Signals ...........................................................................................................................................................................10
Wiring Hookups for Different Sources
Works with Servo Input Only: ..........................................................................................................................................................11
Compatible with SM Series and other Lectrosonics Transmitters: ...................................................................................................11
Wiring Diagram for MI33A Instrument Cable ...................................................................................................................................12
Troubleshooting ....................................................................................................................................................................................13
Specifications and Features
Service and Repair
Returning Units for Repair ............................................................................................................................................................... 15
.........................................................................................................................................................................6
...........................................................................................................................................................................8
........................................................................................................................................................................10
...............................................................................................................................................11
................................................................................................................................................................ 14
...............................................................................................................................................................................15
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LECTROSONICS, INC.
Introduction
Frequency-Agile UHF Belt-Pack Transmitter
Thank you for selecting the Lectrosonics LM or IM
frequency agile, belt-pack transmitter.
The design of these transmitters introduces at a moderate cost the advanced technology and features of a
Lectrosonics belt-pack transmitter. The design is based
on the Digital Hybrid Wireless™ system (US Patent
Pending) which combines a digital audio chain with an
analog FM radio link. This digital process eliminates the
compandor and its problems, yet preserves the extended operating range of the finest analog wireless systems. The IM is offered as part of the IS400 package
and differs slightly from the LM in that its low-frequency
response has been extended for use with musical
instruments.
Both transmitters also preserve your investment. They
can emulate the compandor found in Lectrosonics 100
Series, 200 Series and IFB transmitters, and certain
transmitters from other manufacturers. (Call Lectrosonics for more details.) Changing the compatibility mode
is accomplished with a simple procedure that does not
require opening the unit.
Mechanically, the assemblies are rugged, machined
aluminum packages with removable, stainless steel wire
belt clips. Their input jack is a standard Lectrosonics
5-pin type for use with electret lavaliere mics, dynamic
mics and line level signals. LEDs are provided on the
front panel to make quick and accurate level settings
without having to view the receiver. The battery compartment accepts any 9 volt battery (alkaline or lithium
recommended) and makes a positive connection via
self-adjusting contacts. The antenna is a super-rugged,
permanently attached 1/4 wavelength design made of
flexible galvanized steel cable.
Only the LM and IM transmitters are covered in this
manual. Companion receivers are covered in separate
manuals.
The Digital Hybrid Wireless™ system uses 75 kHz wide
deviation for an extremely high signal to noise ratio. The
switching power supplies provide constant voltages to
the transmitter circuits from the beginning (9.3 VDC)
to the end (5.5 VDC) of battery life. The input amplifier uses an ultra low noise operational amplifier (op
amp) for quiet operation. It is gain controlled with a wide
range dual envelope input limiter that tames input signal
peaks over 30 dB above full modulation.
Digital Hybrid Technology
All wireless links suffer from channel noise to some
degree, and all wireless microphone systems seek to
minimize the impact of that noise on the desired signal.
Conventional analog systems use compandors for
enhanced dynamic range, at the cost of subtle artifacts
(known as “pumping” and “breathing”). Wholly digital
systems defeat the noise by sending the audio information in digital form, at the cost of some combination of
power, bandwidth, operating range and resistance to
interference.
The Lectrosonics Digital Hybrid Wireless™ system
overcomes channel noise in a dramatically new way,
digitally encoding the audio in the transmitter and
decoding it in the receiver, yet still sending the encoded information via an analog FM wireless link. This
proprietary algorithm is not a digital implementation of
an analog compandor but a technique which can be
accomplished only in the digital domain. (The patent is
still pending, so we cannot publish detailed information.)
Channel noise still has an impact on received signal
quality and will eventually overwhelm the receiver. The
Digital Hybrid Wireless™ system simply encodes the
signal to use a noisy channel as efficiently and robustly
as possible, yielding audio performance that rivals
that of wholly digital systems, without the power, noise
and bandwidth problems inherent in digital transmission. Because it uses an analog FM link, Digital Hybrid
Wireless™ enjoys all the benefits of conventional FM
wireless systems, such as excellent range, efficient use
of RF spectrum, and long battery life. However, unlike
conventional FM systems, Digital Hybrid Wireless™ has
done away with the analog compandor and its artifacts.
Frequency Agility
The transmitter section uses a synthesized, frequency
selectable main oscillator. The frequency is extremely
stable over a wide temperature range and over time.
Two rotary switches, located on the side panel of the
unit, provide 256 frequencies in 100 kHz steps over a
25.5 MHz range. This alleviates carrier interference
problems in mobile or traveling applications.
Wide-Band Deviation
By employing ±75 kHz diviation, Lectrosonics dramatically improves the capture ratio, signal to noise ratio
and AM rejection of our wireless system.
Rio Rancho, NM
Long Battery Life
The use of switching power supplies throughout the
design allows over 6 hours of operation using a single 9
volt alkaline battery and over 13 hours of operation with
a 9 volt lithium battery. The battery contacts are spring
loaded to prevent “rattle” as the unit is handled.
3
LM/IM
Freq
Switches
Bicolor
Modulation
LEDs
9V
Battery
Bicolor
Power
LED
Servo Input
The LMA input is a radically different input system compared to previous Lectrosonics transmitter microphone
inputs. It is so superior that this input system will eventually be utilized by all Lectrosonics UHF transmitters. The
improvements are audible and make the transmitters
easier to use and much harder to overload. It is no
longer necessary on some mics to introduce pads to
prevent overload of the input stage, divide the bias
voltage down for some low voltage mics, or reduce the
limiter range at minimum gain settings.
Input Limiter
The transmitter employs a digitally-controlled analog
audio limiter prior to the analog-to-digital converter.
The limiter has a range greater than 30 dB for excellent
overload protection. A dual release envelope makes
the limiter acoustically transparent while maintaining
low distortion. It can be thought of as two limiters in
series, connected as a fast attack and release limiter
followed by a slow attack and release limiter. The limiter
recovers quickly from brief transients, so that its action
is hidden from the listener, but recovers slowly from
sustained high levels, to both keep audio distortion low
and preserve short term dynamic changes.
No Pre-Emphasis/De-Emphasis
Because the signal to noise ratio of the hybrid system is
so high, there is no need for conventional pre-emphasis
(HF boost) in the transmitter and de-emphasis (HF roll
off) in the receiver. Thus, the possible distortion problems associated with pre-emphasis and de-emphasis
are eliminated.
Pilot Tone Squelch
The hybrid system uses one of 256 different ultrasonic
tones between 25 and 32 kHz, that modulate the carrier
to operate the receiver squelch. The pilot tone frequency is chosen according to which of the 256 channels
has been selected by the frequency switch setting. The
benefit of a pilot tone squelch system is that the receiver will remain muted until it receives the pilot tone from
the matching transmitter, even if a strong RF signal is
present on the carrier frequency of the system.
The 400 Series extends this concept even further by
insuring that all transmitters in a system have different
pilot tone frequencies so that even spurious RF from
the wrong transmitters can’t open the receiver squelch.
Antenna
The antenna consists of a permanently attached flexible, unbreakable 1/4 wavelength galvanized steel cable.
LMa Block Diagram
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LECTROSONICS, INC.
Controls and Functions
Frequency-Agile UHF Belt-Pack Transmitter
Input Jack
The 5-pin (Switchcraft TA5F compatible) input accommodates virtually every lavaliere, hand-held or shotgun
microphone available, and most musical instrument
signals. Line level signals can also be accommodated.
(See 5-Pin Input Jack Wiring.)
Power ON/OFF Switch
The Power ON/OFF switch turns the transmitter on
and off. A pilot tone muting system prevents “thumps”
or transients from occurring at the reciever even if the
transmitter is abruptly switched on or off.
Power LED
The Power LED glows green when the transmitter is
operating and the battery is good. It turns red when
the battery voltage drops to 6.1 VDC and starts blinking
red when the voltage drops to 5.6 VDC. When using a
recommended lithium or alkaline battery, there will be
about 30 minutes of operating time remaining when the
Power LED first begins blinking red.
Note: A weak battery will sometimes cause the
Power LED glow green, but it will soon discharge
to the point where the Power LED will glow red or
go out completely. If in doubt, replace the battery
with a known new battery. If the Power LED fails
to glow when the transmitter is turned on, replace
the battery.
NiMH batteries give little or no warning when they are
depleted. If you wish to use NiMH batteries in the
transmitter, you will need to manually keep track of the
operating time. Start with a fully charged battery, then
measure the time it takes for the Power LED to go out
completely. A number of Lectrosonics receivers incorporate a Battery Timer function which tracks the amount
of time the transmitter signal is detected (See your receiver manual to determine if this function is available.)
By using the receiver’s battery timer and replacing the
transmitter battery before the premeasured time is up,
users can minimize potential loss of audio when NiMH
batteries are used.
Frequency Select Switches
Two 16-position rotary Frequency Select Switches, accessed through the left side panel, are used to adjust
the transmitter’s operating frequency. These switches
are labeled 1.6M and 100K. The 1.6M switch is used
for coarse frequency adjustments and the 100K is used
for fine frequency adjustment.
Modulation LEDs
The Modulation LEDs provide a visual indication of the
input audio signal level from the microphone or musical
isntrument. These two bicolor LEDs can glow either red
or green to indicate modulation levels.
Rio Rancho, NM
(LM Shown for illustrative purposes)
AUDIO LEVEL
control
Power LED
Antenna
Battery Compartment Door
Frequency Select
Switches
The Modulation LEDs are also used to indicate the
Compatibility Mode when the transmitter is initially
turned on. The Modulation LEDs will blink simultaneously:
• Once for 100 Series mode
• Two times for 200 Series mode
• Three times for mode 3
• Four times for Digital Hybrid Wireless™
or 400 Series mode
• Five times for IFB mode
Belt Cip
Attachment
Input Jack
Modulation
LEDs
Power
ON/OFF
Audio Level
The AUDIO LEVEL control is used to set the level of the
transmitter’s input for the proper modulation.
Antenna
The flexible, insulated galvanized steel cable antenna
supplied with the transmitter is cut to 1/4 wavelength of
the center of the frequency block (the frequency range)
of the transmitter.
Belt Clip
The belt clip may be removed for special applications
by pulling the ends out of the holes in the sides of the
case. An optional hinged belt clip (P/N BCHINGED) is
also available. Contact a Lectrosonics sales representative, or visit our web site (www.lectrosonics.com) for
more details.
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