4
UT400
LECTROSONICS, INC.
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
Battery
Switching
Power
Supply
+3.3v
+1.8v
+9v
-3v
Audio
Encoded
Audio +
Pilot Tone
11.3 MHz
Reference
Bicolor
Power
LED
Audio
Level
Input
Amp
Final
Amplifier
50
Isolator
Preamp
Mic
Element
Preamp
Level
Tone
GENERAL TECHNICAL DESCRIPTION
GENERAL
The 400 system uses 75 kHz 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 V) to the end (5.5 V) 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 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 Wireless
TM
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. (As of this writing, the patent is still pending, so we cannot reveal detailed informa-
tion 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 perfor-
mance that rivals that of wholly digital systems, without the power and bandwidth problems inherent in digital trans-
mission. 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 fre-
quency 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 sys-
tems, the Digital Hybrid has done away with the analog compandor and its artifacts.
Содержание UT400
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