User's Manual

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,efcient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