Lectrosonics UH400 - Manual (Page 3)

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 con­
stant 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, band­
width 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 propri­
etary 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 ana­
log 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 prob­
lems 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 excel­
lent 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.
Transmitter
Phase Locked Loop
Voltage
Controlled
Oscillator
Freq
Switches
11001001
A-D
Converter
Digital Signal Processor
11001001
D-A
Converter
Shunt
Limiter
Bicolor
Modulation
LEDs
Microprocessor
9V
Switching
Power
Supply
+3.3v
+3.2v
+1.8v
+6v
-3v
50
Isolator
Hi/Lo
Pass
Filter
Audio
Encoded
Audio +
Pilot Tone
11.3 MHz
Reference
Bicolor
Power
LED
Audio
Level
Input
Amp
INPUT
JACK
+5V / +15V / +48V
BIAS SUPPLY
<-- (See Input Jack under Controls and Functions for details.)
UH400 Block Diagram
Rio Rancho, NM – USA 3