Lectrosonics MM200 User Manual

MM200

FREQUENCY-AGILE UHF MINIATURE

BELT-PACK TRANSMITTER

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

www.lectrosonics.com

TABLE OF CONTENTS

INTRODUCTION ................................................................................................... 3

GENERAL TECHNICAL DESCRIPTION ............................................................. 3

CONTROLS AND FUNCTIONS ........................................................................... 6

BATTERY INSTALLATION .................................................................................... 8

OPERATING INSTRUCTIONS ............................................................................. 8

OPERATING NOTES ............................................................................................. 8

ADJUSTING THE TRANSMITTER FREQUENCY .............................................. 9

MICROPHONE RF Bypassing.............................................................................. 9

TROUBLESHOOTING......................................................................................... 10

SPECIFICATIONS AND FEATURES ................................................................. 11

SERVICE AND REPAIR ...................................................................................... 12

RETURNING UNITS FOR REPAIR .................................................................... 12

WARRANTY ........................................................................................... Back cover

The MM200 transmitter is FCC type accepted under Part 74: 536-608 MHz and 614-806 MHz

WARNING! TO PREVENT INTERNAL CORROSION!

If the transmitter is wet (either due to immersion or high levels of perspiration),
BEFORE opening any covers or connectors, carefully blot the transmitter dry with
a clean paper towel or cloth. Remove all moisture. After opening any connector
or cover, carefully blot up any remaining moisture that may have remained around
the seal. THIS IS IMPORTANT! DO NOT CLOSE ANY COVER OR CONNEC­TOR BEFORE MAKING CERTAIN THERE IS NO MOISTURE IN OR NEAR
THE OPENING. After use, it is important to store the transmitter in a dry place
with all access doors and connectors opened to allow any internal humidity to
evaporate. Specifically, open the battery door, the frequency cover plate and fully
unscrew and remove the microphone connector before storing. Do NOT store wet
and do NOT store sealed. If moisture is sealed inside the unit it has nowhere to go
other than to chemically react with and destroy components and the printed circuit
board.

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Frequency Agile UHF Miniature Belt-Pack Transmitter

INTRODUCTION

Thank you for selecting the Lectrosonics MM200 frequency agile UHF miniature
transmitter. The MM200 combines over 80 years of engineering experience with the
very latest components, in a design that addresses the most demanding profes­sional applications.

The design of the MM200 was the direct result of numerous conversations with
users, staging and touring companies and dealers across the US. The specific
concerns and needs brought up in these conversations led directly to the develop­ment of the operational features offered on the MM200. Two hundred fifty six fre­quencies are user selectable in 100kHz steps to alleviate interference problems in
traveling venues.

The MM200 is a rugged, machined stainless steel package with a removable, spring
loaded belt clip. 3.3 Volts of bias voltage is available to power electret mics. Level
indicating LEDs are provided on the control panel to make level settings quick and
accurate, without having to view the receiver. The battery compartment accepts AA
alkaline or lithium batteries. The antenna is a detachable, locking ¼ wavelength
flexible bronze cable that connects to a 50 Ohm SMA port on the transmitter.

Only the MM200 transmitter is covered in this manual. Companion receivers are
covered in separate manuals. The transmitter will operate with any 200 Series
Lectrosonics receiver in the same frequency group.

The MM200 transmitter uses a Digital Signal Processor to model the dual band
compander used in the 200 series with the appropriate compandor time constants
and frequency division. Since the signals are converted from analog to digital,
processed and then converted back to analog, there is a delay as with all digital
audio systems. This delay is 1.6 mS or an equivalent audio path length delay
of 1.8 ft.

Rio Rancho, NM – USA

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GENERAL TECHNICAL DESCRIPTION

If the unit will be used in a wet environment (possible immersion, perspiration, rain scenes, etc.) – be certain all
connectors have intact gaskets and that a properly sealed Lectrosonics’ waterproof mic connector is installed and
used with the microphone.

GENERAL

The 200 system uses 75kHz wide deviation for an extremely high signal to noise ratio. The 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. The input amplifier uses an ultra low noise op amp for quiet operation. It is gain controlled with a wide range dual
envelope input compressor which cleanly limits input signal peaks over 30dB above full modulation.

DUAL BAND COMPANDOR MODELING in the MM200

Traditionally, compandors have been a source of distortion in wireless microphone systems. The basic problem with
conventional systems is that the attack and decay times are always a compromise. If the time constants are fast,
high frequency transients will not be distorted, but this will cause low frequency distortion. If the time constants are
slower, low frequency audio distortion will be low, but high frequency transients will then be distorted. The 200
system introduces an entirely new approach to solving this basic problem, called “dual-band companding.”

There are actually two separate compandors in the 200 system, one for high frequencies and one for low frequen­cies. A crossover network separates the frequency bands at 1kHz with a 6dB per octave slope, followed by separate
high and low frequency compandors. The attack and release times in the high frequency compandor are fast enough
to keep high frequency transient distortion at a low level, and the low frequency compandor uses slower time con­stants, reducing low frequency distortion to well below that of a conventional compandor.

NO PRE-EMPHASIS/DE-EMPHASIS

The signal to noise ratio of the 200 system is high enough to preclude the need for conventional pre-emphasis (HF
boost) in the transmitter and de-emphasis (HF roll off) in the receiver. Pre-emphasis and de-emphasis in an FM
radio system usually provides about a 10dB improvement in the signal to noise ratio of the system, but the high
frequency boost in the transmitter must be removed in a purely complementary manner or else the frequency
response of the original audio signal will be altered.

+3V Bias

Mic

Jack

(Fits Switchcraft

plug #850.)

Supply

Hi/Lo
Pass
Filter

Bicolor

Modulation

LEDs

Shunt

Limiter

Input
Amp

Audio
Level

Freq

Switches

Audio

Microprocessor

A-D

Converter

11001001

Digital Signal Processor

D-A

Converter

11001001

Encoded

Audio +

Pilot Tone

1.5V
AA

Lithium

Switching

Power

Supply

Bicolor
Power
LED

+3.3v
+3v
+1.8v
+6v

-3v

MM200 Block Diagram

4

Phase Locked Loop

4MHz

Reference

Voltage

Controlled

Oscillator

Transmitter

50

Isolator

Frequency Agile UHF Miniature Belt-Pack Transmitter

Pre-emphasis can also cause distortion in the receiver. As this signal is passed through the IF filters in the receiver,
distortion can be produced, most noticeable at full modulation. De-emphasis cannot be applied until the signal is
converted into audio, so there is no way around this problem short of eliminating pre-emphasis altogether. Neither of
these problems occur in the 400 system. The dual-band compandor in the modeled 200 Series system essentially
provides a dynamic pre-emphasis/de-emphasis function with low distortion.

LOW FREQUENCY ROLL-OFF

A 12 dB per octave low frequency roll-off is provided in the audio section, with the -3dB 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 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. In sound reinforce­ment systems, as one instance, excessive low frequency content can cause excessive power amplifier drain or even
damage to loudspeaker systems.

PILOT TONE SQUELCH

The 200 system utilizes an ultrasonic tone that modulates the carrier to operate the receiver squelch. The “pilot tone”
frequency is 32.765 kHz which is low enough to be passed by the system but not so low that it can be heard. The
pilot tone squelch system will keep the receiver 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.

WIDE-BAND DEVIATION

±75kHz deviation improves the capture ratio, signal to noise ratio and AM rejection of a wireless system dramatically,
compared to the more commonly used ±15kHz deviation.

BATTERY LIFE

Switching power supplies throughout the design allow about 4.5 hours of operation using a single AA lithium battery.
(An alkaline or NiMh AA battery will provide about 2 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 rotary switches, located on the side panel of the unit, provide 256
frequencies in 100kHz steps over a 25.5MHz range. This alleviates carrier interference problems in mobile or
traveling applications.

CIRCULATOR

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

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