Lectrosonics UM300b User Manual

UM300B

FREQUENCY-AGILE UHF

BELT-PACK TRANSMITTER

EURO MODEL

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

www.lectrosonics.com

0885

TABLE OF CONTENTS

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

GENERAL TECHNICAL DESCRIPTION ............................................................. 4

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

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

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

OPERATING NOTES ............................................................................................. 9

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

MICROPHONE CORD TERMINATION .............................................................. 10

5-PIN INPUT JACK WIRING............................................................................... 11

A6U UHF ANTENNA ........................................................................................... 13

TROUBLESHOOTING ......................................................................................... 14

SPECIFICATIONS AND FEATURES.................................................................. 15

SERVICE AND REPAIR ........................................................................ Back cover

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

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Frequency Agile UHF Belt-Pack Transmitter

INTRODUCTION

Thank you for selecting the Lectrosonics UM300B frequency agile, belt-pack trans­mitter. The UM300B 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 UM300B 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 UM300B. Up to two hundred fifty six
frequencies are user selectable to alleviate interference problems in travelling
venues, and the low frequency roll-off is user adjustable to adapt to varying acoustic
environments and preferences.

The UM300B 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 bronze cable that connects to a 50 Ohm SMA
port on the transmitter.

Only the UM300B transmitter is covered in this manual. Companion receivers are
covered in separate manuals. The UM300B will operate with any 300 Series Lec­trosonics receiver in the same frequency group.

Lectro Model: UM300B
Int. App No: RO192WM
Modulation Type: 180KF3E
Freq. Range: 844.8 - 862 MHz
Ser. No: XXXXXX - Block 33

Rio Rancho, NM – USA

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GENERAL TECHNICAL DESCRIPTION

The UM300B transmitters are comprised of a number of functional sub-systems as shown in the block diagram
below.

GENERAL

The 300 system uses 50kHz 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 (6.5 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 300
system introduces an entirely new approach to solving this basic problem, called “dual-band companding.”

There are actually two separate compandors in the 300 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.

MIC

JACK

1
2
3
4
5

FREQ

SWITCHES

LIMIT

LED

+5V BIAS

SUPPLY

BUFFER

SHUNT

LIMITER

SYNTHESIZER

uP

LF
ROLL-OFF

INPUT
AMP

AUDIO
LEVEL

SET
LED

LOW PASS

FILTER

2

E PROM

LP

FILTER

PEAK AUDIO

INDICATOR &

LIMITER

DRIVER

COMPANDOR

Vref

BASS

TREBLE

COMPANDED

LP FILTER

HP FILTER

AUDIO

UM300B Block Diagram

PILOT
TONE

OSC

Vreg

+5VDC

Vreg

+3.6VDC

VOLTAGE

CONTROLLED

OSCILLATOR

COMPANDED AUDIO

PWR

TRANSMITTER

TO XMTR

DELAY

+9VDC

PWR

LED

4

Frequency Agile UHF Belt-Pack Transmitter

NO PRE-EMPHASIS/DE-EMPHASIS

The signal to noise ratio of the 300 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 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 300 system. The dual-band compandor in the 300 Series system essentially provides a
dynamic pre-emphasis/de-emphasis function with extremely low distortion.

PILOT TONE SQUELCH

The 300 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 that include an automatic microphone mixer.

WIDE-BAND DEVIATION

±50kHz 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.

LONG BATTERY LIFE

High efficiency circuits throughout the design allow over 7hours of operation using a single 9 Volt alkaline battery. (A
9V lithium battery will provide over 17 hours of operation.) The battery compartment is a unique mechanical design
which automatically adjusts to fit any brand of battery. 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 a maximum of 256 frequencies in 25kHz steps
minimum over a maximum range of 25.5MHz. This alleviates carrier interference problems in mobile or travelling
applications.

ANTENNA

At UHF frequencies, where wavelengths and antennas are shorter than at VHF frequencies, a resonant length wire is
preferred over using the microphone cable as the antenna. The antenna on the UM300B consists of a flexible 1/4
wavelength bronze cable, detachable via an SMA connector. The impedance of this connector is 50 Ohms.

Rio Rancho, NM – USA

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