Lectrosonics R400 - Manual (Page 4)

R400
GENERAL TECHNICAL DESCRIPTION
INTRODUCTION RF FRONT-END AND MIXER
The R400 is a high performance, triple-conversion,
frequency synthesized UHF receiver fully compatible
with all Lectrosonics 400 Series Digital Hybrid Wireless
TM
transmitters, 200 and 100 Series analog transmitters,
plus analog transmitters from other manufacturers (call
Lectrosonics for details). The R400 features 256 user
selectable frequencies and its proprietary audio process­
ing includes a digital signal processor (DSP) for very low
distortion and a superior signal to noise ratio with audio
output adjustable from -50 dBu to +5 dBu in 1 dB incre­
ments.
The R400 features a menu-driven LCD graphic display,
a pushbutton POWER/PREV MENU control and a dual
function (push/rotate) PUSH FOR MENU/ROTATE TO
SELECT control (hereafter called the MENU control) as
a convenient means of viewing and altering user set­
tings. For example, the Main Window displays the pilot
tone indicator, antenna diversity phase, RF level, audio
level, operating frequency, transmitter Frequency Select
Switch settings and transmitter battery status.
The MENU control provides simple and intuitive access
to change and adjust settings and operating levels.
Pushing the MENU control from the Main Window enters
the Top Menu which displays a choice of four submenu
selections: SetUpRx, LockSet, Scan, and Exit. Each
subsequent push of the MENU control moves into
another menu layer. Rotating the MENU control either
selects a submenu or sets a functional parameter.
DIVERSITY RECEPTION
SMART Diversity TM minimizes dropouts in situations
where multi-path reflections can cause serious problems.
The phase diversity network and PIN diode RF switches
are controlled by the microprocessor using a sophisti­
cated algorithm to use both antennas simultaneously.
The R400 is frequency agile and can be set to operate
on any one of 256 frequencies within its tuning range. To
significantly reduce unwanted interference and inter-
modulation problems, the R400 has a front-end section
that tunes 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 selectivity.
A LC bandpass filter after the RF amplifier provides
added insurance against strong RF interference. The
first mixer uses new GaAs technology that has a very
high third order intercept point. The overall design
ensures stability, selectivity and precise gain in order to
handle strong RF signals without input overload.
FREQUENCY TUNING GROUPS
The R400 provides four "factory set" compatible fre­
quency groups (A through D) and two user program­
mable frequency groups (U and V).
The factory groups have been selected to avoid inter-
modulation problems. Each group includes eight fre­
quencies.
The user programmable frequency groups can have up
to 16 frequencies per group.
MICROPROCESSOR, PLL AND VCO
CIRCUITS
An 8-bit microprocessor monitors user command inputs
from the front panel control buttons and numerous other
internal signals such as RF level, audio levels, pilot tone
levels and external power voltages. The microprocessor
also drives the LCD display, controls the squelch and
audio output attenuator, and operates the PLL/VCO
circuits and the antenna phase switch.
50
50
5K
5K
uP
LCD
Display
Panel
PILOT TONE
DETECT
FILTER
DIGITAL SIGNAL
PROCESSOR
Attenuation
CERAMIC
FILTER
2ND
MIXER
10.7 MHZ
SAW
FILTER
244 MHz
IF AMP
A-D
CONVERTER
D-A
CONVERTER
2nd
VCO
FILTER
AMP
XLR
OUT
HI-LEVEL
MIXER
RF MODULE
3RD MIXER
AND
IF AMP
50KHz
LP FILTER
XTAL
CONTROLLED
3rd
OSCILLATOR
SAW
FILTER
244 MHz
IF AMP
COUNTING
DETECTOR
AUDIO
AMP
R400
BLOCK DIAGRAM
ANTENNA
COMBINING
FILTER
E PROM 2
1st
VCO
Smart Diversity
PLL
SYNTHESIZER
LC
Filter
Output
Level
Adjust
Digital
Attenuator
2 (HI)
1 (COMMON)
3 (LO)
4