Lectrosonics SM User Manual
SM
Super Miniature Belt-Pack Transmitter
INSTRUCTION MANUAL
With Digital Hybrid Wireless™ Technology
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Rio Rancho, NM, USA
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SM
Thank you for selecting the Lectrosonics SM ultra-miniature transmitter. The unique design provides several
distinct features for professional applications:
Outstanding RF operating range
Superb audio quality
Ultra-lightweight, corrosion resistant housing
Water resistant seals for use in damp environments
Programmable compatibility modes for maximum
versatility
The Digital Hybrid WirelessTM design (US Patent Pending) combines 24-bit digital audio with analog FM
resulting in a system that has the same operating range
as analog systems (plus the graceful failure at the limits
of that range), the same spectral efficiency as analog
systems, the same long battery life as analog systems,
but with the excellent audio found in digital systems.
The SM uses a standard Lectrosonics 5-pin type input
jack for use with electret lavaliere mic, dynamic mic, or
line level signals. A water resistant control panel with
LCD, membrane switches and multi-color LEDs make
input gain adjustments and frequency and compatibility
mode selection quick and accurate, without having to
view the receiver. The battery compartment accepts
an AA lithium battery. Plus, the SM is machined from
a solid aluminum block to provide an extremely lightweight and rugged package. A special non-corrosive
finish (the same one used by NASA) resists salt water
exposure and perspiration in extreme environments.
The DSP-based design works with all Digital Hybrid recievers, and is backward compatible with Lectrosonics
200 and 100 Series and IFB receivers and some other
brands of analog wireless receivers. Only the SM transmitter is covered in this manual. Companion receivers
are covered in separate manuals.
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LECTROSONICS, INC.
Super-Minature Belt Pack Transmitter
Table of Contents
General Technical Description .............................................................................................................................................................. 4
Introduction ...........................................................................................................................................................................................4
Servo Input............................................................................................................................................................................................4
Digital Hybrid Wireless™ Technology*..................................................................................................................................................4
No Pre-Emphasis/De-Emphasis ...........................................................................................................................................................4
Low Frequency Roll-Off ........................................................................................................................................................................4
Input Limiter ..........................................................................................................................................................................................5
Digital Signal Processor........................................................................................................................................................................ 5
Microprocessor, PLL and VCO Circuits.................................................................................................................................................5
Compatibility Modes..............................................................................................................................................................................5
Pilot Tone Squelch ................................................................................................................................................................................5
Control Panel ........................................................................................................................................................................................5
Wide-Band Deviation ............................................................................................................................................................................5
Battery Life............................................................................................................................................................................................ 5
Frequency Agility...................................................................................................................................................................................5
Circulator/Isolator.................................................................................................................................................................................. 5
Controls and Functions .........................................................................................................................................................................6
LCD Screen ..........................................................................................................................................................................................6
Power LED ............................................................................................................................................................................................6
Audio Input Jack....................................................................................................................................................................................6
Modulation LEDs...................................................................................................................................................................................6
Audio Button .........................................................................................................................................................................................6
Freq Button ...........................................................................................................................................................................................6
Up/Down Arrows ...................................................................................................................................................................................6
Antenna.................................................................................................................................................................................................6
Battery Compartment and Thumb Screw..............................................................................................................................................6
SM Screen Selections ............................................................................................................................................................................7
Audio Screen ........................................................................................................................................................................................7
Frequency Screen.................................................................................................................................................................................7
Compatibility Mode Screen...................................................................................................................................................................7
Lock/Unlock Screen ..............................................................................................................................................................................7
Power On Timer Screen........................................................................................................................................................................7
Power Off Timer Screen........................................................................................................................................................................7
Standby Mode....................................................................................................................................................................................... 8
Remote Control Operation....................................................................................................................................................................8
Battery Installation .................................................................................................................................................................................8
Operating Instructions...........................................................................................................................................................................9
Power Up and Boot Sequence..............................................................................................................................................................9
Power Down..........................................................................................................................................................................................9
Standby Mode....................................................................................................................................................................................... 9
Selecting the Compatibility Mode..........................................................................................................................................................9
Setting Transmitter Operating Frequency............................................................................................................................................10
Attaching a Microphone and Adjusting Gain....................................................................................................................................... 10
Locking or Unlocking the Control Panel .............................................................................................................................................. 11
5-Pin Input Jack Wiring ........................................................................................................................................................................ 12
Microphone RF Bypassing.................................................................................................................................................................. 12
Line Level Signals............................................................................................................................................................................... 12
Wiring Hookups for Different Sources ...............................................................................................................................................13
Troubleshooting....................................................................................................................................................................................14
Specifications and Features................................................................................................................................................................ 17
Service and Repair ...............................................................................................................................................................................18
Returning Units for Repair ..................................................................................................................................................................18
Rio Rancho, NM
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SM
General Technical Description
Introduction
The SM transmitter uses ±75 kHz wide deviation for an
extremely high signal to noise ratio, switching power
supplies to provide constant voltages to the transmitter
circuits from the beginning (1.5 Volts) to the end (0.85
Volts) of battery life, and an ultra low noise input amplifier
for quiet operation. It is gain protected with a wide range
dual envelope input limiter which cleanly limits input
signal peaks over 30 dB above full modulation.
Servo Input
The SM 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.
This may cause some confusion but the advantages are
very real. 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.
Digital Hybrid Wireless™ 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 and resistance to interference.
Lectrosonics Digital Hybrid Wireless™ systems overcome 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 that can be accomplished
only in the digital domain, even though the inputs and
outputs are analog.
Channel noise still impacts received signal quality and
will eventually overwhelm a receiver. Digital Hybrid
Wireless™ 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 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 resistance to interference. However,
unlike conventional FM systems, it does away with the
analog compandor and its artifacts.
No Pre-Emphasis/De-Emphasis
The Digital Hybrid Wireless™ design results in a signalto-noise ratio high enough to preclude the need for
conventional pre-emphasis (HF boost) in the transmitter
and de-emphasis (HF roll off) in the receiver.
Low Frequency Roll-Off
A 12 dB per octave low frequency roll-off is provided in
the audio section, with the -3 dB point at 70 Hz. The
*US Patent Pending
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LECTROSONICS, INC.
Super-Minature Belt Pack Transmitter
actual roll-off frequency will vary somewhat according
to the low frequency response of the mic capsule being
used.
The low frequency roll-off is used to remove subsonic
(or very low frequency) audio, often produced by air
conditioning systems, automobile traffic and other
sources from the audio signal. Excessive low frequency
content in the audio input can cause a variety of audio
problems including driving the transmitter into limiting.
Input Limiter
A DSP-controlled analog audio limiter is employed
before the analog-to-digital converter. The limiter has a
range of more 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.
Two bicolor LEDs indicate limiter activity. (See Operat-
ing Instructions, Adjusting Audio Levels.)
Digital Signal Processor
The DSP encodes the digitized audio from the A-D
Converter and adds an ultrasonic Pilot Tone to control
the receiver’s squelch (only in 400 Series, 200 Series,
IFB Compatibility Mode, and Mode 6 – see Pilot Tone
Squelch). It also controls the input limiter.
Microprocessor, PLL and VCO Circuits
An 8-bit microprocessor monitors user command inputs
from the Control Panel buttons and numerous other
internal signals. It works intimately with the DSP to
ensure the audio is encoded according to the selected
Compatibility Mode and the correct pilot tone is added
to the encoded signal. (See Pilot Tone Squelch.) It
also drives the LCD display and operates the PLL/VCO
circuits.
The 400 Series (Digital Hybrid Wireless™) takes this
a step further by using one of 256 different ultrasonic
tones between 25 kHz and 32 kHz to modulate the
carrier and operate the receiver squelch. The pilot
tone frequency is chosen according to which of the 256
channels has been selected. (See SM Screen Selec-
tions.)
This ensures 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.
Control Panel
A waterproof control panel which includes four membrane switches and an LCD screen is used to set and
adjust the operational settings, and also provide a
visual feedback of overall system operation. (See Con-
trols and Functions.)
Wide-Band Deviation
A ±75 kHz deviation improves the capture ratio, signal
to noise ratio and AM rejection of a wireless system
dramatically, compared to other designs that use 30
kHz to 40 kHz deviation. This combined with a full 100
mW of power output makes a significant improvement in
signal to noise ratio and maximum operating range.
Battery Life
Switching power supplies throughout the design allow
about 4.5 hours of operation using a single AA lithium
battery. If shorter operating times are acceptable, an
alkaline or NiMH battery can be used. AA alkaline batteries provide about 2 hours of operation, and a NiMH
AA battery provides about 3.5 hours of operation.
Note: A NiMH battery will give little or no warning
when it is depleted. If you wish to use NiMH
batteries in the SM, we recommend trying fully
charged batteries in the unit, noting the length of
time that the batteries will run the unit and then
using the battery timer feature available on most
400 Series receivers.
The battery contact is designed to prevent “rattle” as the
unit is handled.
Compatibility Modes
The SM transmitter was designed to operate with Lectrosonics 400 Series receivers and will yield the best
performance when doing so. However, due to the flexibility of digital signal processing, the SM is also able to
operate with Lectrosonics 200 Series, Lectrosonics 100
Series, IFB and certain non-Lectrosonics receivers in
special compatibility modes. (Contact the Lectrosonics
Sales Department for a complete list of non-Lectrosonics compatible receivers.)
Pilot Tone Squelch
A fixed frequency pilot tone squelch system (such
as Lectrosonics 200 Series) ensures that a receiver
remains 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.
Rio Rancho, NM
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.
256 frequencies in 100 kHz steps over a 25.5 MHz
range are available.
Circulator/Isolator
The RF output circuit includes a one way circulator/
isolator using a magnetically polarized ferrite. This
device greatly reduces RF intermodulation produced
when multiple transmitters are used at separations of
less than five feet. It also provides additional RF output
stage protection but is rarely seen in a wireless microphone transmitter due to its high cost.
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SM
Controls and Functions
Modulation
LEDs
Battery
Compartment
Cover Plate
Battery
Compartment
Thumb Screw
PWR LED AUDIO Button FREQ Button
Control Panel
LCD Screen
The LCD is a numeric-type Liquid Crystal Display used
in conjunction with the AUDIO and FREQ buttons, and
the UP and Down arrows, to configure the SM. (See SM
SCREEN SELECTIONS.) It is also used with the Modulation and PWR LEDs to monitor system operation.
Power LED
The PWR LED glows green when the battery is good.
The color changes to red when there is about 30
minutes of operation left with the recommended lithium
battery. (An alkaline battery will have about 20 minutes
of life left.) When the LED begins to blink red, there are
only a few minutes of life.
Note: A NiMH battery will give little or no warning
when it is depleted. If you wish to use NiMH
batteries in the SM, we recommend trying fully
charged batteries in the unit, noting the length of
time that the batteries will run the unit and then
using the battery timer feature available on most
400 Series receivers.
A weak battery will sometimes cause the PWR LED to
glow green immediately after being put in the unit, but
will soon discharge to the point where the LED will go
red or shut off completely. When the SM is in SLEEP
mode, the LED blinks green every few seconds (See
Sleep Mode, page X).
LCD
UP Arrow
Antenna
Audio
Input Jack
Signal Level -20 LED -10 LED
Less than -20 dB Off Off
-20 dB to -10 dB Green Off
-10 dB to +0 dB Green Green
+0 dB to +10 dB Red Green
Greater than +10 db Red Red
Audio Button
The AUDIO button is used to display the audio level setting (0 dB to 44 dB) on the LCD and used in conjunction
with the Up and Down arrows to adjust the audio level
input from the microphone.
The AUDIO button is also used with the FREQ button to
enter standby mode and to power the transmitter on or off.
Freq Button
The SM provides 256 individual frequencies, in 100 kHz
increments, across a 25.5 MHz frequency block. The
FREQ Button displays the selected operating frequency
and also toggles the LCD between displaying the actual
operating frequency in MHz and a two-digit hexadecimal number that corresponds to the equivalent Lectrosonics Frequency Switch Setting.
The FREQ button is also used with the AUDIO button to
enter standby mode and to power the transmitter on or off.
Up/Down Arrows
The Up and Down arrow buttons are used to select the
operating frequency, adjust the audio level, or set the
Compatibility Mode.
Pressing both arrows simultaneously enters the lock
countdown. Holding the two arrow buttons until the
countdown completes locks the control panel buttons so
they can only be used to display current settings. “Loc”
is displayed to indicate the controls are locked.
Once locked, the buttons can be unlocked only by
removing the battery, or via the remote control (if enabled).
Audio Input Jack
The input on the SM accommodates virtually every
lavaliere, handheld or shotgun microphone available.
Different line level signals can also be accommodated.
(See LINE LEVEL SIGNALS and 5-PIN INPUT JACK
WIRING.)
Modulation LEDs
The Modulation LEDs provide a visual indication of the
input audio signal level from the microphone. These
two bicolor LEDs can glow either red or green to indicate modulation levels.
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Antenna
The fixed flexible cable antenna is supplied with the
transmitter. This antenna is cut to the 1/4 wavelength of
the center of the frequency block (the frequency range)
of the transmitter.
Battery Compartment and Thumb Screw
The large knurled thumbscrew is used to release or
secure the Battery Compartment Cover Plate, allowing
access to the battery.
LECTROSONICS, INC.
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