Lectrosonics UM400AV Users Manual
INSTRUCTION MANUAL
UM400a
Frequency Synthesized 100 mW UHF Belt-Pack Transmitter
Featuring
Digital Hybrid Wireless™ Technology
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Rio Rancho, NM, USA
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UM400a
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LECTROSONICS, INC.
Frequency Synthesized UHF Belt-Pack Transmitter
Table of Contents
General Technical Description ..............................................................................................................................................................4
Introduction ...........................................................................................................................................................................................4
Digital Hybrid Technology .......................................................................................................................................................................................... 4
UM400a Block Diagram ........................................................................................................................................................................4
No Pre-Emphasis/De-Emphasis ...........................................................................................................................................................5
Pilot Tone Squelch ................................................................................................................................................................................5
Input Limiter ..........................................................................................................................................................................................5
Wide-Band Deviation ............................................................................................................................................................................5
Batteries, Battery Life and External Power ...........................................................................................................................................5
Frequency Selection .............................................................................................................................................................................5
Antenna .................................................................................................................................................................................................5
Controls and Functions .........................................................................................................................................................................6
Input Jack ..............................................................................................................................................................................................6
Power ON/OFF Switch ..........................................................................................................................................................................6
Power On LED ......................................................................................................................................................................................6
Audio Level Control ...............................................................................................................................................................................6
Modulation LEDs ...................................................................................................................................................................................7
Antenna .................................................................................................................................................................................................7
Frequency Select Switches ...................................................................................................................................................................7
Adjustable Low Frequency Roll-Off .......................................................................................................................................................7
Belt Clip .................................................................................................................................................................................................7
Battery Installation .................................................................................................................................................................................8
Operating Instructions ...........................................................................................................................................................................8
Selecting the Compatibility Mode ..........................................................................................................................................................8
Attaching a Microphone and Adjusting Gain ......................................................................................................................................... 9
Operating Notes .................................................................................................................................................................................... 9
Adjusting the Transmitter Frequency .....................................................................................................................................................9
5-Pin Input Jack Wiring ........................................................................................................................................................................ 10
Microphone Cord Termination .............................................................................................................................................................11
TA5F Connector Assembly .................................................................................................................................................................11
Mic Cord Stripping Instructions ...........................................................................................................................................................11
Microphone RF Bypassing .................................................................................................................................................................. 12
Line Level Signals ...................................................................................................................................................................................
Wiring Hookups for Different Sources ...............................................................................................................................................13
Works with Servo Inputs Only: ............................................................................................................................................................ 13
Compatible with Servo Inputs and other Lectrosonics Transmitters: ...................................................................................................13
Replacement Parts and Accessories ..................................................................................................................................................14
UHF Transmitter Antenna Specifications ............................................................................................................................................14
Troubleshooting ....................................................................................................................................................................................15
Specifications and Features ................................................................................................................................................................ 17
Service and Repair ...............................................................................................................................................................................18
Returning Units for Repair ..................................................................................................................................................................18
© Copyright 2007 Lectrosonics. Inc
Rio Rancho, NM
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UM400a
General Technical Description
Introduction
The UM400a transmitter combines 100 mW of RF
output with +/- 75 kHz wide deviation for extended
operating range and extremely high signal to noise ratio.
These key design features are coupled with the compandor-free Digital Hybrid Wireless® audio chain and
packaged in the widely recognized Lectrosonics standard transmitter housing.
The unit is powered by a single 9V battery in the internal compartment, or from external DC using a Lectrosonics ISO9VOLT battery eliminator.
Digital Hybrid Technology
All wireless links suffer from channel noise to some
degree, and all wireless microphone systems seek
to minimize the impact of that noise on the desired
signal. Conventional analog systems use compandors
to improve the signal to noise ratio, at the cost of subtle
artifacts (known as “pumping” and “breathing”). Wholly
digital systems defeat the noise by sending the audio
information in digital form, at the cost of some combination of power, bandwidth and resistance to interference.
The Lectrosonics Digital Hybrid system overcomes
channel noise in a dramatically new way, digitally
encoding the audio in the transmitter and decoding it
in the receiver, yet still sending the encoded informa-
tion via an analog FM wireless link. This proprietary
algorithm is not a digital implementation of an analog
compandor but a technique which can be accomplished
only in the digital domain, even though the inputs and
outputs are analog signals.
Channel noise still has an impact on received signal
quality and will eventually overwhelm the receiver. The
Digital Hybrid simply encodes the signal to use a noisy
channel as efficiently and robustly as possible, yielding audio performance that rivals that of wholly digital
systems, without the power and bandwidth problems
inherent in digital transmission. As always, these
advantages come at a cost. The Digital Hybrid system
requires fairly intensive digital processing in both the
transmitter and the receiver. These processors cost
money, take up space and consume power. The Digital
Hybrid system also requires that the underlying RF link
be of excellent quality, with better frequency response
and distortion characteristics than that required by conventional systems.
Because it uses an analog FM link, the Digital Hybrid
enjoys all the benefits of conventional FM wireless
systems, such as excellent range, efficient use of RF
spectrum, and long battery life. However, unlike conventional FM systems, this unique design has done
away with the analog compandor and its artifacts.
UM400a Block Diagram
<--See 5-Pin Input Jack Wiring for details.
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LECTROSONICS, INC.
Frequency Synthesized UHF Belt-Pack Transmitter
No Pre-Emphasis/De-Emphasis
The signal to noise ratio of the hybrid 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 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 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 noticeably 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
hybrid system design.
Pilot Tone Squelch
The system uses one of 256 different ultrasonic tones
between 25 and 32 kHz, that modulate the carrier to
operate the receiver squelch. The pilot tone frequency
is chosen according to which of the 256 channels has
been selected by the frequency switch setting. The purpose 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. The
UM400a extends this concept even further by ensuring
that all transmitters in a system have different pilot tone
frequencies so that even spurious RF from the wrong
transmitters can’t open the receiver squelch.
Wide-Band Deviation
± 75 kHz deviation improves the capture ratio, signal to
noise ratio and AM rejection of a wireless system dramatically, compared to the more commonly used ±15
kHz deviation.
Frequency Selection
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 100 kHz steps over a
25.5 MHz range. This alleviates carrier interference
problems in mobile or traveling applications.
Antenna
The antenna on the UM400a consists of a rugged 1/4
wavelength stranded and galvanized steel cable, detachable via an SMA connector. The impedance of this
antenna port is 50 Ohms.
Input Limiter
The transmitters employ a digitally-controlled analog
audio limiter just before the analog-to-digital converter.
The limiter has a range of more than 30 dB for excellent
overload protection. A dual release envelope makes
the limiter acoustically transparent while maintaining
low distortion. It can be thought of as two limiters in
series, connected as a fast attack and release limiter
followed by a slow attack and release limiter. The limiter
recovers quickly from brief transients, so that its action
is hidden from the listener, but recovers slowly from
sustained high levels, to both keep audio distortion low
and preserve short term dynamic changes.
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 recorders and many sound reinforcement systems.
Rio Rancho, NM
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UM400a
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Controls and Functions
Input Jack
Power LED
Power ON/OFF Switch
AUDIO LEVEL Control
Modulation LEDs
ANTENNA Jack
Input Jack
The input on the UM400a accommodates virtually every
lavaliere, hand-held or shotgun microphone available.
Different line level signals can also be accommodated.
(See Wiring Hookups for Different Sources.)
Power ON/OFF Switch
Turns the transmitter on and off. Even when the switch
is turned off or on abruptly, the pilot tone muting system
prevents “thumps” or transients from occurring.
Power On LED
The Power LED glows green when the battery is good
and the transmitter is turned on. The LED will glow
yellow/orange as the battery voltage drops and finally
glows red when there are about 30 minutes of operation
left (when using the recommended battery). The LED
blinks red when there are only a few minutes of life left.
Low Frequency Roll Off
Control
1.6M 100K
Frequency Select Switches
NOTE: While a NiMH battery provides long
operating time, it will give little or no warning
when depleted. If you use a NiMH battery in the
UM400a, we recommend trying a fully charged
battery in the unit, noting the length of time that
the battery will run the unit and in the future use
somewhat less than that time to determine when
the battery needs to be replaced.
A weak battery will sometimes light the Power LED to
the “good” green indication immediately after being put
in the unit, but will quickly discharge to the point where
the LED will go red or shut down (just like a flashlight
with “dead” batteries). If the lamp fails to light, the battery should be replaced.
Audio Level Control
The front panel AUDIO LEVEL Control is used to adjust
the incoming audio input level for proper modulation.
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LECTROSONICS, INC.
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