Lectrosonics UM195 User Manual

UM195

BELT-PACK TRANSMITTER

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

INTRODUCTION

Thank you for selecting the Lectrosonics UM195 belt-pack transmitter. The UM195 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 UM195 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 UM195. This is certainly not the first belt­pack transmitter ever designed, but it is definitely the most thoroughly engineered unit available.

The UM195 is a rugged, machined aluminum package with a removable, spring loaded belt clip. The input section
provides a correct input tap for virtually any microphone or line level audio source. 5 Volts of bias voltage is
available to power electret mics with either positive or negative bias. 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 any 9 Volt alkaline battery and makes a positive connection via self-adjusting contacts. The
antenna is a detachable, locking 1/4 wavelength flexible wire that connects to a 50 Ohm port on the transmitter.

Only the UM195 transmitter is covered in this manual. Companion receivers are covered in separate manuals.
The UM195 will operate with any 195 Series Lectrosonics receiver on the same frequency.

TABLE OF CONTENTS

INTRODUCTION .......................................... 1

GENERAL TECHNICAL DESCRIPTION .......................... 2

CONTROLS AND FUNCTIONS ................................ 4

BATTERY INSTALLATION ................................... 6

OPERATING INSTRUCTIONS ................................. 7

OPERATING NOTES ....................................... 7

M195 INPUT JACK WIRING .................................. 8

TROUBLESHOOTING ....................................... 9

SPECIFICATIONS AND FEATURES ............................ 10

SERVICE AND REPAIR ..................................... 11

RETURNING UNITS FOR REPAIR ............................. 11

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

The UM195 transmitter is FCC type accepted under Part 74: 470-608 MHz; 174-216 MHz

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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

SHUNT

LIMITER

LF
ROLL-OFF

INPUT
AMP

LIMIT

LED

SET
LED

AUDIO
LEVEL

INDICATOR &

FILTER

PEAK AUDIO

LIMITER
DRIVER

LP

Vref

COMPANDOR

BASS

TREBLE

LP FILTER

HP FILTER

Vreg

Vreg

PILOT
TONE

OSC

+5VDC

+3.6VDC

COMPANDED AUDIO

TO XMTR

MUTE

PWR

SWITCH
DISABLE

+9VDC

PWR

LED

LED

DISABLE

1
2
3
4
5

MIC

JACK

COMPANDED

AUDIO

Figure 1 - UM195 Block Diagram

2

XTAL OSC

X4

X2

X2

UHF TRANSMITTER

X2

The signal to noise ratio of the 195 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.

Pre-emphasis can also cause distortion in the IF filtering stage in a 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 pre­emphasis altogether. Neither of these problems occur in the 195 system. The dual-band compandor in the 195
Series system essentially provides a dynamic pre-emphasis/de-emphasis function with extremely low distortion.

The 195 system utilizes an ultrasonic tone modulation of the carrier to operate the receiver squelch. This "pilot
tone" consists of a 32kHz signal mixed with the audio signal following the microphone preamp, just after the
compandor, to control the audio output muting of the receiver. The pilot tone is filtered out of the audio signal
immediately after the detector in the receiver so that it does not influence the compandor or various gain stages.
The basic benefit of the pilot tone squelch system is that 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.
This is extremely important in applications such as with an automatic sound system.

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. 75kHz deviation is frequently used in the UHF spectrum, but it is
much harder to implement at VHF frequencies. The 195 system is the first to take advantage of this wider
deviation now allowed by the FCC in the VHF spectrum. Almost all other VHF wireless systems use 15kHz
deviation.

High efficiency circuits throughout the design allow over 7 hours of operation on the UHF version, and over 10
hours on the VHF versions, using a single 9 Volt alkaline battery. The battery compartment is a unique mechanical
design which automatically adjusts to fit any brand alkaline battery. The battery contacts are spring loaded to
prevent "rattle" as the unit is handled.

The transmitter section uses a crystal stabilized main oscillator followed by a quadrupler and three doubler stages.
The crystal controlled frequency is extremely stable over a wide temperature range and over time. Double tuning
used in the multiplier stages provides higher attenuation of spurious emissions which, in turn, minimizes the
possibility that the transmitter RF output would interfere with another transmitter/receiver system operating in the
same vicinity.

At UHF frequencies, where wavelengths and antennas are shorter than VHF, a resonant dangling wire is preferred.
The antenna on the UM195 consists of a flexible 1/4 wavelength wire, detachable via a twist lock connector. The
impedance of this connector is 50 Ohms at UHF frequencies.

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