Lectrosonics UH400 User Manual

UH400

FREQUENCY-AGILE

PLUG-ON UHF TRANSMITTER

OPERATING INSTRUCTIONS

and trouble-shooting guide

LECTROSONICS, INC.

Rio Rancho, NM

www.lectrosonics.com

UH400

INTRODUCTION

Thank you for selecting the Lectrosonics UH400 frequency agile, plug-on transmitter. The
UH400 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 UH400 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
UH400. Two hundred fifty six frequencies are user selectable in 100kHz steps to alleviate
interference problems in travelling venues.

The UH400 is a rugged, machined aluminum package. Selectable voltage phantom power is
provided on pins 2 and 3. Level indicating LEDs are provided 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.

Only the UH400 transmitter is covered in this manual. Companion receivers are covered in
separate manuals. The UH400 will operate with any 100, 200 or 400 Series Lectrosonics
receiver in the same frequency group.

TABLE OF CONTENTS

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

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

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

OPERATING INSTRUCTIONS ............................................................................... 6

TROUBLESHOOTING ............................................................................................8

SPECIFICATIONS AND FEATURES .................................................................. 10

SERVICE AND REPAIR ...................................................................................... 11

RETURNING UNITS FOR REPAIR ..................................................................... 11

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

The UH400 transmitter is FCC type accepted under Part 74: 470 - 608MHz and 614 - 806MHz

2

LECTROSONICS, INC.

Frequency Agile Plug-on UHF Transmitter

GENERAL TECHNICAL DESCRIPTION

GENERAL

The 400 system uses 75kHz wide deviation for an extremely high
signal to noise ratio. 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 30dB 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 dynamic range, 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 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. (As of this writing, the patent is still pending, so we
cannot reveal detailed information about the algorithm at this
time.)

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.

INPUT

JACK

+5V / +15V / +48V
BIAS SUPPLY

Hi/Lo
Pass
Filter

Bicolor

Modulation

LEDs

<-- (See Input Jack under Controls and Functions for details.)

Shunt

Limiter

Switches

Phase Locked Loop

11.3 MHz

Reference

Input

Amp

Freq

Audio
Level

Audio

Converter

11001001

Microprocessor

A-D

Digital Signal Processor

Controlled

D-A

Converter

11001001

Voltage

Oscillator

Encoded

Audio +

Pilot Tone

9V

Transmitter

Switching

Power

Supply

Isolator

50

+3.3v
+3.2v
+1.8v
+6v

-3v

Bicolor
Power
LED

UH400 Block Diagram

Rio Rancho, NM – USA

3

UH400

0

1

2
3

4
5
6

7

8

9

A

B

C

D

E

F

0

1

2
3

4
5
6

7

8

9

A

B

C

D

E

F

NO PRE-EMPHASIS/DE-EMPHASIS

The signal to noise ratio of the 400 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. Pre­emphasis 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 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 pre­emphasis altogether. Neither of these problems occur in the 400
system

PILOT TONE SQUELCH

The 400 system utilizes 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. The UH400

extends this concept even further by insuring 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

±75kHz 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

Switching power supplies throughout the design allow over 4.5
hours of operation using a single 9 Volt alkaline battery. (A 9V
lithium battery will provide over 12 hours of operation.) 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 traveling
applications.

CONTROLS AND FUNCTIONS

MODULATION LEDs

–10

–20

POWER
ON/OFF
LED

INPUT
JACK

MIC LEVEL

Top View

This transmitter may be used with a wide variety of microphones.
The 3-pin XLR connector allows the transmitter to be used with
any dynamic microphone, as well as many two wire positive bias
lavaliere systems (such as those systems supplied by Lectroson­ics).

POWER SWITCH

Turns the battery power on and off. Even when the switch is
turned off or on abruptly, the pilot tone muting system prevents
“thumps” or transients from occurring.

The PHTM (center) position of the power switch turns on the
phantom power while the NO PHTM (fully on) position disables
phantom power. Be careful to use the center position phantom

N O PHTM

P HTM

PWR OFF

LEVEL

Control Panel

INPUT

JACK

FREQUENCY

1.6MHz 100kHz

FREQUENCY SWITCHES

(BEHIND DOOR)

5V

48 V

1 5V

POWER
SWITCH

PHANTOM POWER
VOLTAGE SELECT

Side View

power only when necessary and keep the voltage selector switch
in the 5 Volt position for additional protection against accidents.

POWER ON/OFF LED

This LED glows green when the battery is good. When the lamp
glows red, there is about 30 minutes of operation left with the
recommended lithium battery, and about 20 minutes of life left
with an alkalline battery. The lamp will flash red when there are
only a few minutes of life remaining. A NiMh battery will give little
or no warning when it is depleted. If you wish to use NiMh
batteries in this unit, we recommend trying fully charged batteries
in the unit, noting the length of time that the batteries 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

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LECTROSONICS, INC.