UHF Wireless Digital Hybrid
TM
Receiver
GENERAL TECHNICAL DESCRIPTION
The UCR411 is a portable, high performance, triple-
conversion, frequency synthesized, UHF receiver fully
compatible with all Lectrosonics 400 series transmitters.
The RF performance is extremely stable over a very
wide temperature range, making the UCR411 perfectly
suited to the rough environmental conditions found in the
field. The proprietary audio processing includes a digital
signal processor for very low distortion and a superior
signal to noise ratio.
The UCR411 features a menu-driven LCD graphic
display and a three button control panel as a convenient
means of viewing and altering user settings. The main
window, for example, shows the pilot tone indicator,
antenna diversity phase, RF level, audio level, receiver
battery status and transmitter battery status. It is also
possible to bypass the pilot tone from the main display
window. Other display windows show operating fre
quency, audio output level, battery status in tenths of
volts and test tone status. The frequency scan mode
provides a spectrum analyzer for a graphical means of
observing all signals “on the air” within the frequency
range of the receiver in order to find operating frequen
cies that are free of interference.
DIVERSITY RECEPTION
The UCR411 technology with 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 con
trolled by the microprocessor using a sophisticated
algorithm to use both antennas simultaneously. This
design keeps the receiver compact enough for camera
mounting or shoulder bag applications, yet provides
effective diversity reception.
RF FREQUENCY TRACKING FRONT-END
AND MIXER
The receiver 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
intermodulation problems, the UCR411 has a frequency
selective front-end section that tracks and tunes to the
desired signal frequency and rejects or “tunes out”
unwanted interfering signals. The design consists of four
varactor tuned ceramic transmission line resonators
controlled by the microprocessor to provide good selec
tivity. The low noise high current RF amplifier was
designed with feedback regulation for stability and
precise gain in order to handle stronger RF signals
without output overload. The first mixer is of new GaAs
technology that has a very high third order intercept
point. This produces a robust front-end that is as selec
tive as fixed single frequency designs and is suitable for
use in close proximity to other receivers and transmitters
commonly used in field production “bag” systems.
MICROCONTROLLER, PLL AND VCO
CIRCUITS
The 8-bit microprocessor is truly the “heart” of the
UCR411 receiver. It 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/internal power voltages. Outputs
from the microcontroller drive the LCD display and
backlight, control the squelch and audio output attenua
tor, and operate the front-end tuning, the PLL/VCO
circuits and the antenna phase switch. The UCR411
design and the advanced technology of the microproces
sor control arguably set a new standard in wireless
microphone development.
IF AMPLIFIERS AND SAW FILTERS
The first IF low noise amplifier is controlled with feed
back regulation and drives the first of two quartz SAW
(Surface Acoustical Wave) filters. The 244 MHz SAW
filters combine sharp tuning, constant group delay, wide
bandwidth and excellent temperature stability, far supe
rior to conventional LC filters. The 244 MHz first IF
signal is converted to 10.7 MHz, filtered through two
ceramic filters for sharp selectivity, then converted to 300
kHz in one integrated circuit.
DIGITAL PULSE COUNTING DETECTOR
The UCR411 receiver uses an elegantly simple, yet
highly effective digital pulse detector to demodulate the
FM signal, rather than a conventional quadrature detec
tor. This unusual design eliminates thermal drift, im
proves AM rejection, and provides very low audio
distortion.
DSP-BASED PILOT TONE
The 400 Series system design utilizes a DSP generated
ultrasonic pilot tone to control the receiver audio muting
(squelch). Brief delays at turn-on and turn-off eliminate
thumps, pops or other transients that can occur when the
power is switched on or off. The pilot tone frequency is
different for each of the 256 frequencies in the tuning
range of a system (frequency block.) This eliminates
squelch problems in multichannel systems where a pilot
tone signal can appear in the wrong receiver via inter-
modulation products. The DSP generated pilot tone also
eliminates the need for fragile crystals allowing the
receiver to survive shocks and mishandling much better
than older analog-based pilot tone systems.
Rio Rancho, NM – USA
3
