Introduction - Lectrosonics R400A Instruction Manual

R400A

Introduction

The R400A is a high performance, triple-conversion,
frequency synthesized UHF receiver fully compatible
with all Lectrosonics 400 Series Digital Hybrid Wire-
less transmitters, 200 Series and 100 Series analog
®
transmitters and Lectrosonics IFB transmitters, plus
some analog transmitters from other manufacturers
(call Lectrosonics for details). The R400A features 256
user selectable frequencies and its proprietary audio
processing includes a digital signal processor (DSP)
for very low distortion, a superior signal to noise ratio
and two independent audio outputs, one balanced and
one unbalanced.
The receiver features a menu-driven LCD graphic dis-
play, a push-button POWER/PREV MENU control and
a dual function (push/rotate) PUSH FOR MENU/RO-
TATE TO SELECT control (hereafter called the MENU
control) as a convenient means of viewing and altering
user settings.
The MENU control provides simple and intuitive ac-
cess to change and adjust settings and operating lev-
els. Pushing the MENU control from the Main Window
enters the Top Menu which displays a choice of five
submenu options: SetUpRx, LockSet, SmartTune™,
Scan and Exit. Rotating the MENU control either
highlights a menu option or sets a parameter. Pushing
the MENU control either selects the highlighted menu
option or enters (or reenters) a menu.
Digital Hybrid Wireless
Lectrosonics Digital Hybrid Wireless
7,225,135) uses innovative technology to combine
the new advantages of digital audio with the classic
advantages of analog RF transmission. The result is
the superior sound quality of a digital system and the
excellent range of an analog system. A proprietary
algorithm encodes the digital audio information into
an analog format which can be transmitted in a robust
manner over an analog FM wireless link. The receiver
employs the latest filters, RF amplifiers, mixers and
detector to capture the encoded signal and a DSP
(Digital Signal Processor) recovers the original digital
audio.
This digital/analog hybrid technique has some very
beneficial properties. Because the information being
transmitted is digitally encoded, immunity to noise is
much higher than a compandor-based system can
offer and no artifacts are introduced under strong RF
conditions, and spectral and power efficiency and
operating range are not compromised.
Diversity Reception
SMARTDiversity minimizes dropouts in situations
™
where multi-path reflections can cause serious prob-
lems. The phase diversity network and PIN diode RF
switches are controlled by the microprocessor using a
sophisticated algorithm to use both antennas simulta-
neously.
4
®
(US Patent
®
RF Front-End and Mixer
The R400A is frequency agile and can be set to oper-
ate on any one of 256 frequencies within its tuning
range.
To significantly reduce unwanted interference and
intermodulation problems, the R400A's front-end is
tuned to the desired frequency band and rejects or
"tunes out" unwanted out-of-band signals. Two tuned
HI-Q ceramic transmission line resonators prior to a
low noise, high current RF amplifier provide good se-
lectivity. A robust RF amplifier and LC bandbass filter
provide added insurance against strong RF interfer-
ence. The overall design ensures stability, selectivity
and precise gain in order to handle strong RF signals
without input overload.
IF Amplifiers and SAW Filters
The first IF low noise amplifier is controlled with
feedback regulation and drives a quartz SAW (Sur-
face Acoustical Wave) filter. The 244 MHz SAW filter
combines sharp tuning, constant group delay, wide
bandwidth and excellent temperature stability, far
superior to conventional LC filters. The second mixer
converts the 244 MHz first IF signal down to 10.7 MHz.
The second IF is filtered through two ceramic filters for
sharp selectivity, then itself is converted down to 300
kHz and fed to the Digital Pulse Counting Detector.
Digital Pulse Counting Detector
The R400A receiver uses an elegantly simple, yet
highly effective digital pulse detector to demodulate
the FM signal, rather than a conventional quadrature
detector. This unusual design eliminates thermal drift,
improves AM rejection, and provides very low audio
distortion. The output from the Digital Pulse Counter is
an analog signal containing the digital audio informa-
tion. This signal is fed through a low pass filter to an
A-D Converter in the Digital Signal Processing section.
Frequency Tuning Groups
The R400A provides four "factory set" compatible
frequency groups (A through D) and two user program-
mable frequency groups (U and V).
The factory groups have been selected to avoid
intermodulation problems. Each group includes eight
channels.
The user programmable frequency groups can have up
to 16 frequencies per group.
LECTROSONICS, INC.