Lectrosonics UH400a User Manual download pdf (Page 4)

UH400A/UH400TM

General Technical Description

UH400A Block Diagram

Introduction

Digital Hybrid Wireless

™

is a wideband design with

±75 kHz deviation produding an excellent audio signal

to noise ratio and wide dynamic range. The switching

power supplies provide constant voltages to the trans-

mitter circuits from the beginning (9.3 Volts) to the end

(5.5 Volts) of battery life. The input ampliﬁer uses an

ultra low noise op amp for quiet operation. It is gain con-

trolled with a wide range dual envelope input compres-

sor 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 signal to noise ratio, 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 combina-

tion of power, bandwidth and resistance to interference.

The Lectrosonics Digital Hybrid Wireless

™

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 implementa-

tion 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, yield-

ing 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 con-

ventional 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 con-

ventional FM systems, the Digital Hybrid has done away

with the analog compandor and its artifacts.

LECTROSONICS, INC.

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