Lectrosonics MM400a - Manual - Manual (Page 4)

MM400A
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 (1.5 Volts) to the end (0.85
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 WIRELESS TM
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 informa­
tion 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 encod­
ing 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 resistance to interference. However,
unlike conventional FM systems, the Digital Hybrid has
done away with the analog compandor and its artifacts.
MM400
*US Patent Pending
Transmitter
Block Diagram
Phase Locked Loop
Voltage
Controlled
Oscillator
Freq
Switches
(Fits Switchcraft
plug #850.)
11001001
A-D
Converter
Digital Signal Processor
11001001
D-A
Converter
Shunt
Limiter
Bicolor
Modulation
LEDs
Microprocessor
1.5V
AA
Lithium
Switching
Power
Supply
+3.3v
+3v
+1.8v
+6v
-3v
50
Isolator
Hi/Lo
Pass
Filter
Audio
Encoded
Audio +
Pilot Tone
4MHz
Reference
Bicolor
Power
LED
Mic
Jack
+6V Bias
Supply
Audio
Level
Input
Amp
<--See Input Jack Wiring for details.
LECTROSONICS, INC. 4