Lectrosonics UM195 User Manual download pdf (Page 4)

GENERAL TECHNICAL DESCRIPTION

The UM195 transmitters are comprised of a number of functional sub-systems as shown in the block diagram

below.

The 195 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 (7 Volts) of battery life. The oscillator

crystal is shock mounted to provide ruggedness. The input amplifier uses a Motorola 33078 op amp for ultra low

noise operation. It is gain controlled with a wide range input compressor which cleanly limits input signal peaks

over 40dB above full modulation.

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 195 system introduces an entirely new approach to solving this basic problem, called "dual-band companding."

There are actually two separate compandors in the 195 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

PWR

MUTE

+9VDC

XTAL OSC

UHF TRANSMITTER

Vref

LP FILTER

HP FILTER

SET

LED

LIMIT

LED

COMPANDOR

Vreg

+5VDC

+3.6VDC

SHUNT

LIMITER

INPUT

AMP

AUDIO

LEVEL

FILTER

PEAK AUDIO

INDICATOR &

LIMITER

DRIVER

PILOT

TONE

OSC

MIC

JACK

ROLL-OFF

COMPANDED AUDIO

TO XMTR

SWITCH

DISABLE

PWR

LED

DISABLE

COMPANDED

AUDIO

BASS

TREBLE

Figure 1 - UM195 Block Diagram

1 2 3 4 5 6 7 8 9 ... 13 14

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Lectrosonics UM195 User Manual Page 4

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