Lectrosonics UM190b User Manual

UM190B

UHF BELT-PACK TRANSMITTER

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

INTRODUCTION

Thank you for selecting the Lectrosonics UM190B belt-pack transmitter. The UM190B
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 UM190B was the direct result of numerous conversations with users
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 UM190B. This is certainly not
the first belt-pack transmitter ever designed, but it is definitely the most thoroughly
engineered unit available.

The UM190B 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 is available on the input connector 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 or lithium 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 UM190B transmitter is covered in this manual. Companion receivers are
covered in separate manuals.

The UM190B will operate with any 190 Series Lectrosonics receiver on a matching
frequency.

TABLE OF CONTENTS

INTRODUCTION .................................................................................................. 2

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

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

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

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

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

MICROPHONE CORD TERMINATION ............................................................... 8

UM190B INPUT JACK WIRING ........................................................................... 9

TROUBLESHOOTING ....................................................................................... 11

SPECIFICATIONS AND FEATURES ................................................................. 12

SERVICE AND REPAIR ..................................................................................... 13

RETURNING UNITS FOR REPAIR ................................................................... 13

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

The UM190B transmitter is FCC type accepted under Part 74: 470-608 MHz

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UHF Belt-Pack Transmitter

GENERAL TECHNICAL DESCRIPTION

The UM190B transmitter is comprised of a number of functional sub-systems as shown in the block diagram below.

The 190 system uses 15kHz deviation. 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 30dB 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 190 system intro­duces an entirely new approach to solving this basic problem, called “dual-band companding.”

There are actually two separate compandors in the 190 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.

High efficiency circuits throughout the design allow over 7 hours of operation using a single 9 Volt alkaline battery
(over 16 hours with a lithium 9V 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 UHF 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 UHF version of the UM190B consists of a flexible ¼ wavelength wire, detachable via an SMA
connector. The impedance of this connector is 50 Ohms at UHF frequencies.

+5V BIAS

SUPPLY

BUFFER

LIMIT

LED

LF
ROLL-OFF

INPUT
AMP

SET
LED

AUDIO
LEVEL

PEAK AUDIO
INDICATOR &

LIMITER
DRIVER

LP

FILTER

Vref

TREBLE

COMPANDOR

BASS

COMPANDED

AUDIO

LP FILTER

HP FILTER

Vreg

Vreg

+5VDC

+3.6VDC

X4

OFF

ON

-9V

X2 X2 X2

+9VDC

PWR
LED

1
2
3
4
5

MIC

JACK

SHUNT

LIMITER

UM190B Block Diagram

Rio Rancho, NM – USA

XTAL OSC

UHF TRANSMITTER

3

CONTROLS AND FUNCTIONS

LECTROSONICS

UM190

OFF ON

B

75 Hz

35

150

LF ROLL OFF

AUDIO
LEVEL

ANTENNA

0

–20

LF

ROLL-OFF

ADJ

INPUT JACK

The input on the UM190B accommodates virtually every lavalier, hand-held or shotgun microphone available. Use a
Switchcraft TA5F connector on the cord. See the separate sheet titled “Transmitter 5-Pin Input Jack Wiring”
regarding the correct connections for various microphones, and other sources.

ON/OFF SWITCH

Turns the battery power on and off.

“ON” LAMP

Glows brightly when the battery is good. A weak or dim lamp means that the battery is weak, and has about half an
hour of operation left. If the lamp fails to light, the battery should be replaced.

The “ON” lamp is connected to a precision battery test circuit that continuously monitors battery voltage. The LED is
at full brightness with a new 9 Volt battery. As the battery voltage drops during use, the LED brightness will also
decrease. When the LED is barely visible, there will still be 30 minutes or more operating time remaining.

Since the internal circuits are all tightly regulated and the RF output stage has a separate discrete regulator, the
transmitter will continue to operate to a battery voltage of 6.5 Volts. From 6.5 Volts to 6 Volts, the transmitter will still
operate, but with degraded performance. Please note that a weak battery will sometimes light the POWER LED
immediately after turn on, but will soon discharge to the point where the LED will go out, just like a flashlight with
“dead” batteries.

The combination of an accurate battery condition indicator and regulation of all internal circuits provides much longer
battery life, as well as consistent performance over the life of the battery.

4

UHF Belt-Pack Transmitter

MODULATION LEDS

Indicate the proper setting of the MIC LEVEL control.

LEVEL LED — Flickers or glows when sufficient audio is present.
LIMIT LED — Lights up when the input level is high enough to cause limiting. The input limiter has a very high

overload threshold (over 30 dB). Generally speaking, some limiting is desirable in normal operation to improve the
signal to noise ratio of the system. The limiting action is not audible and does not create distortion. A highly
trained ear would hear only the compression of the peaks in the audio signal, which is desirable with most tape
recorders and many sound reinforcement systems.

MIC LEVEL

Used to adjust the audio input level for the proper modulation.

ANTENNA JACK

The flexible wire antenna supplied with the UM190B UHF transmitter is cut to 1/4 wavelength. It is removable via an
SMA connector. The 50 Ohm RF port can also be connected directly to test equipment.

ADJUSTABLE LOW FREQUENCY ROLL-OFF

A 18dB per octave low frequency roll-off is provided in the audio section, with the -3dB point adjustable from 35Hz to
150Hz. 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 control is used to prevent undesirable subsonic (or very low frequency) audio, often pro­duced by air conditioning systems, automobile traffic and other sources from causing the compandor to mistrack.
Excessive low frequency content in the audio input can cause “pumping and breathing” of background noise or
modulation of the program audio in recording applications. In sound reinforcement systems, excessive low frequency
content can cause excessive power amplifier drain or even damage to loudspeaker systems. By rotating the control
clockwise, the hinge point of the roll-off is increased to reduce the level of low frequencies. In controlled situations,
such as a motion picture production set indoors where environmental noise is minimal, the control can be rotated
counter-clockwise to permit low frequency audio to be captured.

THE BELT CLIP

The belt clip may be removed for special applications by removing one screw.

USE ONLY THE SCREW THAT IS SUPPLIED

The circuitry is tightly packed into this unit. A longer screw will permanently damage the transmitter!

Rio Rancho, NM – USA

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