Lectrosonics UH400a User Manual
UH400A
UH400TM
Frequency Agile Plug-On UHF Transmitter
INSTRUCTION MANUAL
Featuring Digital Hybrid Wireless™ Technology
U.S. Patent 7,225,135
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Rio Rancho, NM, USA
www.lectrosonics.com
UH400A/UH400TM
This plug-on transmitter is an advanced design that
has evolved since the first models appeared in the late
1980’s serving ENG applications at television stations
across the USA. In the mid-1990’s, the first UHF versions became available and the use of plug-on transmitters in motion picture production increased significantly.
The current UH400A model has evolved to include
every improvement and feature developed since the first
model was introduced.
The UH400A is a rugged, machined aluminum package with selectable phantom power for use with a wide
variety of microphones. LEDs located on the top panel
make quick and accurate level settings without having
to view the receiver. The battery compartment accepts
any 9 volt alkaline, LiPolymer or lithium battery and
makes a positive connection via self-adjusting contacts.
The UH400TM is a specialized version of the UH400A
that is an integral part of a highly accurate wireless test
and measurement system.
Only the UH400A and UH400TM transmitters are covered in this manual. Companion receivers are covered
in separate manuals. The UH400A and UH400TM will
operate with any 100 Series, 200 Series, 400 Series,
IFB Lectrosonics receiver in the same frequency group,
or selected analog receivers from other manufacturers
operating in the same frequency range. (Contact factory for details.)
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LECTROSONICS, INC.
Frequency Agile Plug-On UHF Transmitter
Table of Contents
General Technical Description ..............................................................................................................................................................4
Introduction ...........................................................................................................................................................................................4
Digital Hybrid Technology .....................................................................................................................................................................4
Input Limiter ..........................................................................................................................................................................................5
No Pre-Emphasis/De-Emphasis ...........................................................................................................................................................5
Pilot Tone Squelch ................................................................................................................................................................................5
Long Battery Life................................................................................................................................................................................... 5
Frequency Agility...................................................................................................................................................................................5
Controls and Functions .........................................................................................................................................................................6
Power Switch ........................................................................................................................................................................................6
Power ON/OFF LED .............................................................................................................................................................................6
Phantom Power Voltage Select Switch .................................................................................................................................................6
Frequency Select Switches...................................................................................................................................................................7
Input Jack..............................................................................................................................................................................................7
Modulation LEDs...................................................................................................................................................................................7
Input Signal Level..................................................................................................................................................................................7
Input Gain Adjustment ..........................................................................................................................................................................7
Compatibility Mode Indicators............................................................................................................................................................... 8
Block Numbers and Freqeuncy Ranges...............................................................................................................................................9
Operating Instructions.........................................................................................................................................................................10
Attaching the Microphone ...................................................................................................................................................................10
Selecting the Compatibility Mode........................................................................................................................................................10
Adjusting the Transmitter Frequency...................................................................................................................................................11
Battery Replacement ..........................................................................................................................................................................11
Using the Polarity- Reversing Barrel Adapter....................................................................................................................................12
Accessories ..........................................................................................................................................................................................12
Troubleshooting....................................................................................................................................................................................13
Specifications and Features................................................................................................................................................................ 14
Service and Repair ...............................................................................................................................................................................15
Returning Units for Repair ..................................................................................................................................................................15
Rio Rancho, NM
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UH400A/UH400TM
General Technical Description
UH400A Block Diagram
Introduction
Digital Hybrid Wireless™ is a wideband design with
±75 kHz deviation produding an excellent audio signal
to noise ratio and wide dynamic range. The switching
power supplies provide constant voltages to the transmitter circuits from the beginning (9.3 Volts) to the end
(5.5 Volts) of battery life. The input amplifier uses an
ultra low noise op amp for quiet operation. It is gain controlled with a wide range dual envelope input compressor which cleanly limits input signal peaks over 30 dB
above full modulation.
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
for enhanced 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 Wireless™ system
(hereafter called Digital Hybrid) 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 information 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, the Digital Hybrid has done away
with the analog compandor and its artifacts.
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LECTROSONICS, INC.
Frequency Agile Plug-On UHF Transmitter
Input Limiter
The Digital Hybrid Wireless™ 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.
No Pre-Emphasis/De-Emphasis
The signal to noise ratio of the Digital Hybrid Wireless
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 Digital Hybrid system.
Wide-Band Deviation
A ±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.
Long Battery Life
Switching power supplies throughout the design allow
over 4.5 hours of operation using a single 9 Volt alkaline 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 100 kHz steps over a
25.5 MHz range. This alleviates carrier interference
problems in mobile or traveling applications.
™
Pilot Tone Squelch
The Digital Hybrid Wireless™ 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 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.
Rio Rancho, NM
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