Lectrosonics MM400C, Instruction Manual

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MM400C
LECTROSONICS, INC.
6
General
The 400 Series (or Digital Hybrid Wireless ® ) 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 be-
ginning (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.
Note: The terms 400 Series and Digital Hybrid
Wireless ® describe the same product line are
interchangeable.
Digital Hybrid Wireless
®
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 Wireless
®
system over-
comes 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 informa-
General Technical Description
tion 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.
Because it uses an analog FM link, Digital Hybrid Wire -
less
®
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.
Low Frequency Roll-Off
A 12 dB per octave low frequency roll-off is provided in
the audio section, with the -3 dB point at 70 Hz. The
actual roll-off frequency will vary somewhat according
to the low frequency response of the mic capsule being
used.
The low frequency roll-off is used to remove subsonic
(or very low frequency) audio, such as that produced by
air conditioning systems or automobile traffic from the
audio signal. Excessive low frequency content in the
audio input can cause a variety of audio problems in-
cluding driving the transmitter into limiting. For exam -
ple, in sound reinforcement systems, as one instance,
excessive low frequency content can cause excessive
power amplifier drain or even damage to loudspeaker
systems.
+5V Bias
11.3 MHz