Lectrosonics MM400c User Manual download pdf (Page 6)

MM400C

LECTROSONICS, INC.

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 and 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 wire-

less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

including driving the transmitter into limiting. In sound

reinforcementsystems,asanotherinstance,excessive

lowfrequencycontentcancauseexcessivepoweram-

pliﬁer drain or even damage to loudspeaker systems.

+5V Bias

11.3 MHz

1 2 3 4 5 6 7 8 9 10 11 ... 19 20

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