Lectrosonics UM100 User Manual
UM100
UHF MULTI-FREQUENCY
BELT-PACK TRANSMITTER
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
Rio Rancho, NM
TABLE OF CONTENTS
INTRODUCTION .................................................................................................. 3
GENERAL TECHNICAL DESCRIPTION ............................................................ 4
CONTROLS AND FUNCTIONS .......................................................................... 6
BATTERY INSTALLATION ................................................................................... 8
OPERATING INSTRUCTIONS ............................................................................ 9
OPERATING NOTES ........................................................................................... 9
ADJUSTING THE TRANSMITTER FREQUENCY .............................................. 9
MICROPHONE CORD TERMINATION ............................................................. 10
5-PIN INPUT JACK WIRING.............................................................................. 11
TROUBLESHOOTING ....................................................................................... 13
SPECIFICATIONS AND FEATURES ................................................................ 14
SERVICE AND REPAIR ..................................................................................... 15
RETURNING UNITS FOR REPAIR ................................................................... 15
WARRANTY ......................................................................................... Back cover
The UM100 transmitter is FCC type accepted under Part 74: 470-608MHz and 614-802MHz
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Multi-frequency UHF Belt-Pack Transmitter
INTRODUCTION
Thank you for selecting the Lectrosonics UM100 multi-frequency, belt-pack transmitter. The UM100 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 UM100 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 UM100. Two hundred fifty six frequencies are user selectable in 100kHz steps 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 UM100 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 fixed 1/4
wavelength flexible bronze cable.
Only the UM100 transmitter is covered in this manual. Companion receivers are
covered in separate manuals. The UM100 will operate with any 100 Series Lectrosonics receiver in the same frequency group.
Rio Rancho, NM – USA
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GENERAL TECHNICAL DESCRIPTION
The UM100 transmitters are comprised of a number of functional sub-systems as shown in the block diagram below.
GENERAL
The 100 system uses 20 kHz wide deviation for a 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 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.
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 100 system
introduces an entirely new approach to solving this basic problem, called “dual-band companding.”
There are actually two separate compandors in the 100 system, one for high frequencies and one for low frequencies.
A crossover network separates the frequency bands at 1 kHz with a 6 dB 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
MIC
JACK
1
2
3
4
5
PHASE LOCKED LOOP
FREQ
SWITCHES
SUPPLY
BUFFER
SHUNT
LIMITER
DIVIDER
LF
ROLL-OFF
INPUT
AMP
LIMIT
LED
SET
LED
AUDIO
LEVEL
PEAK AUDIO
INDICATOR &
LIMITER
DRIVER
PRESCALER
LOW PASS
FILTER
LP
FILTER
COMPANDOR
Vref
BASS
TREBLE
COMPANDED
LP FILTER
HP FILTER
AUDIO
UM100 Block Diagram
PWR
VOLTAGE
CONTROLLED
OSCILLATOR
COMPANDED AUDIO
TRANSMITTER
PWR
LED
TO XMTR
Vreg
Vreg
+9VDC
+5VDC
+3.6VDC
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Multi-frequency UHF Belt-Pack Transmitter
PRE-EMPHASIS/DE-EMPHASIS
The signal to noise ratio of the 100 system is extended by using pre-emphasis (HF boost) in the transmitter and deemphasis (HF roll off) in the receiver. Pre-emphasis and de-emphasis in an FM radio system usually provides about
a 10 dB improvement in the signal to noise ratio of the system, but the high frequency boost in the transmitter must
be removed in a purely complimentary manner or else the frequency response of the original audio signal will be
altered. The dual-band compandor in the 100 system essentially provides a dynamic pre-emphasis/de-emphasis
function with low distortion.
LONG BATTERY LIFE
High efficiency circuits throughout the design allow over 4.5 hours of operation using a single 9 Volt alkaline battery.
(A 9V lithium battery will provide over 14 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 256 frequencies in 100kHz steps over a 25.5MHz
range. 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 UM100 consists of a flexible 1/4
wavelength bronze cable.
Rio Rancho, NM – USA
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