General Technical Description - Lectrosonics UM200 Operating Instructions Manual

Frequency-agile, belt-pack transmitter

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Table Of Contents

Table of Contents

The UM200 transmitters are comprised of a number of functional sub-systems as shown in the block diagram

below.

GENERAL

The 200 system uses 75kHz wide deviation for an extremely high signal to noise ratio. The transmitter circuits are

all regulated to allow full output power from the beginning (9 Volts) to the end (6 Volts) of battery life. The input

amplifier uses a Motorola 33178 op amp for ultra low noise operation. It is gain controlled with a wide range input

compressor which cleanly limits input signal peaks over 30dB above full modulation.

DUAL BAND COMPANDOR

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.

+5V BIAS

SUPPLY

MIC

JACK

ROLL-OFF

INPUT

AMP

LIMIT

LED

SHUNT

LIMITER

SET

LED

PHASE LOCKED LOOP

DIVIDER

FREQ

SWITCHES