Lectrosonics SMV User Manual

Frequency Agile UHF Ultra-Miniature Belt-Pack Transmitter

SM

DIGITAL HYBRID WIRELESS

TM

ULTRA-MINIATURE

UHF BELT-PACK TRANSMITTER

OPERATING INSTRUCTIONS

Professional Audio Products Since 1971

Rio Rancho, NM

www.lectrosonics.com

Rio Rancho, NM – USA

1

SM

The SM transmitter is FCC type accepted under Part 74: 536-608 MHz and 614-806 MHz

2

Professional Audio Products Since 1971

Frequency Agile UHF Ultra-Miniature Belt-Pack Transmitter

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 techniques
resulting 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, 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 alkaline, lithium or NiMH 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 on NASA space vehicles) resists salt water exposure and perspiration in extreme environments.

The DSP-based design offers backward compatibility with Lectrosonics 100 and 200 Series 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.

TABLE OF CONTENTS

GENERAL TECHNICAL DESCRIPTION ...................................................................................................... 4

GENERAL ...................................................................................................................................................................... 4

DIGITAL HYBRID WIRELESS™ TECHNOLOGY .......................................................................................................... 4

NO PRE-EMPHASIS/DE-EMPHASIS ............................................................................................................................ 4

LOW FREQUENCY ROLL-OFF ..................................................................................................................................... 5

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

PWR LED ....................................................................................................................................................................... 6

AUDIO INPUT JACK ...................................................................................................................................................... 6

MODULATION LEDS ...................................................................................................................................................... 6

AUDIO BUTTON............................................................................................................................................................. 6

FREQ BUTTON .............................................................................................................................................................. 6

UP/DOWN ARROWS ..................................................................................................................................................... 7

ANTENNA ...................................................................................................................................................................... 7

BATTERY COMPARTMENT AND THUMB SCREW ..................................................................................................... 7

SM SCREEN SELECTIONS .......................................................................................................................... 8

FREQUENCY SCREEN ................................................................................................................................................. 8

AUDIO SCREEN ............................................................................................................................................................ 8

COMPATIBILITY MODE SCREEN ................................................................................................................................. 8

LOCK/UNLOCK SCREEN .............................................................................................................................................. 8

POWER OFF TIMER SCREEN...................................................................................................................................... 8

BATTERY INSTALLATION ............................................................................................................................ 9

OPERATING INSTRUCTIONS .................................................................................................................... 10

POWER UP AND BOOT SEQUENCE ......................................................................................................................... 10

POWER DOWN ............................................................................................................................................................ 10

SELECTING THE COMPATIBLITY MODE .................................................................................................................. 10

SETTING TRANSMITTER OPERATING FREQUENCY ............................................................................................. 11

ATTACHING A MICROPHONE AND ADJUSTING GAIN ............................................................................................ 11

LOCKING OR UNLOCKING THE CONTROL PANEL ................................................................................................. 12

OPERATING NOTES ................................................................................................................................... 12

5-PIN INPUT JACK WIRING ....................................................................................................................... 13

MICROPHONE RF BYPASSING ................................................................................................................................. 13

LINE LEVEL SIGNALS ............................................................................................................................................ 14

WIRING HOOKUPS FOR DIFFERENT SOURCES .............................................................................................. 14

TROUBLESHOOTING ................................................................................................................................. 15

SPECIFICATIONS AND FEATURES .......................................................................................................... 16

SERVICE AND REPAIR ............................................................................................................................... 17

RETURNING UNITS FOR REPAIR ............................................................................................................. 18

LIMITED ONE YEAR WARRANTY .............................................................................................................. 20

Rio Rancho, NM – USA

3

SM

GENERAL TECHNICAL DESCRIPTION

GENERAL

The 400 system uses ±75 kHz wide deviation for an
extremely high signal to noise ratio. Switching power
supplies 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 op amp is
used as the 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.

The terms 400 Series and Digital Hybrid Wireless™ describe the

same product line and are interchangeable.

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

Note

™

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
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

Bias

Vol tage

Mic

Jack

1
2

3

4
5

0, 2 or 4 Volts

Shunt
Limiter

Servo Bias

Input

Amp

LCD

Audio

Switch

Freq

Switch

Bicolor

Powe r

LED

Bicolor

Modulation

LEDs

Supply

Digital

Pot

Up/Down
Switches

Audio
Level

Hi/Lo
Pass
Filter

+6v

Audio

Microprocessor

Control Panel

A-D

Converter

11001001

Digital Signal Processor

Phase Locked Loop

Reference

Crystal

D-A

Converter

11001001

Encoded
Audio and
Pilot Tone

1.5V

Battery

Switching

Powe r

Supply

SM

Block Diagram

+3.3v
+1.8v
+6v

-3v

Vol tage

Controlled

Oscillator

Final

Amplifier

50

Ohms

Isolator

*US Patent Pending

4

Professional Audio Products Since 1971

Frequency Agile UHF Ultra-Miniature Belt-Pack Transmitter

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 digitally-controlled analog audio limiter is employed
just 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

Instructions, Adjusting Audio Levels

.)

Operating

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
and IFB Compatibility Modes with the Pilot Tone enabled
– see

Pilot Tone Squelch

).

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 endocded signal. (See
drives the LCD display, controls the Pilot Tone, operates
the PLL/VCO circuits.

Pilot Tone Squelch

.) It also

COMPATIBILITY MODES

The SM transmitter was designed to be compatible 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
compatible receivers.)

PILOT TONE SQUELCH

The Digital Hybrid Wireless™ 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 via the Control
Panel mounted FREQ switch. (See

tions

.) The pilot tone squelch system ensures 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. 400
Series Compatibility Mode 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.

SM Screen Selec-

CONTROL PANEL

A waterproof control panel which includes four mem­brane switches and an LCD screen is used to change
and control the operational settings, and also provide a
visual feedback of overall system operation. (See

Controls 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. An alkaline AA battery provides about 2 hours,
and a NiMH AA battery provides about 3.5 hours of
operation. The battery contacts are spring loaded to
prevent “rattle” as the unit is handled.

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 membrane switches, located on the Control Panel,
provide 256 frequencies in 100 kHz steps over a 25.5
MHz range.

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.

Rio Rancho, NM – USA

5

SM

CONTROLS AND FUNCTIONS

Battery Compartment

Cover Plate

Battery Compartment

Thumb Screw

Modulation LEDs

-10

-20

PWR LED

Audio Button

Freq Button

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.

LCD

Antenna

Audio Input Jack

Up/Down Buttons

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.

PWR 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 flicker red, there are
only a few minutes of life.

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.

Note

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.

AUDIO INPUT JACK

The input on the SM accommodates virtually every
lavaliere, hand-held or shotgun microphone available.
Different line level signals can also be accommodated.
(See

LINE LEVEL SIGNALS

WIRING

.)

and

5-PIN INPUT JACK

Signal Level

Less than -20 dB

-20 dB to -10 dB

-10 dB to +0 dB
+0 dB to +10 dB
Greater than +10 dB

-20 LED

Off
Green
Green
Red
Red

-10 LED

Off
Off
Green
Green
Red

AUDIO BUTTON

Pressing the AUDIO button alone causes the LCD to
display the audio level setting (0 dB to 44 dB). This level
is adjustable via the Up and Down arrows.

Simultaneously pressing the AUDIO button and FREQ
button will 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 toggles the LCD between displaying the
actual operating frequency in MHz or a two-digit hexa­decimal number that corresponds to the equivalent
Lectrosonics Frequency Switch Setting.

6

Professional Audio Products Since 1971