How to get the most from your RX Lectrosonics UCR411
The UCR411A receiver provides professional performance
and a versatile feature set in a compact design for field
and location production. All settings are made from the
front panel with a powerful LCD interface, making the unit
ideal for use in portable bag systems, on sound carts, and
in rack mount multi-couplers. An RF spectrum analyzer
is built into the receiver to alleviate interference problems
in an increasingly congested RF spectrum. The receiver
tunes across its 25.6 MHz tuning range and records RF
activity with markers on the LCD screen. Finding clear
operating frequencies is a quick, simple process.
The mechanical design of the receiver combines field
proven features developed over many years of experience
in motion picture and television production markets. The
machined aluminum housing and panels are surfaced with
electrostatic powder coated and anodized finishes with laser
etched markings to withstand the rigors of field production.
DSP Compatibility Modes
The native, compandor-free Digital Hybrid operating
mode works with all Lectrosonics hybrid transmitters. DSP
"compatibility modes" allow the receiver to also work with
companded analog transmitters from Lectrosonics and
some from other manufacturers. This expands the usefulness
of the receiver and provides the backward compatibility
needed to give existing customers an economical
Frequency Tracking Front-End Filters
The front-end consists of four transmission line resonators
to each resonator to
retune it as the frequency
The tuning range covers
a full 25.6 MHz
block of frequencies.
The design provides
filtering as selective
as most fixed frequency designs, with the overload
performance of the best front-ends available. The result is
extended operating range in even the most congested RF
*US Patent 7,225,135
Digital Hybrid Wireless™ technology* is a revolutionary
new design that combines digital audio with an
analog FM radio link to provide outstanding audio
quality and the exemplary RF performance of the finest
analog wireless systems.
The design 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 implementation of
an analog compandor. Instead, it is a technique which
can be accomplished only in the digital domain.
The process eliminates a compandor and its artifacts,
expanding the applications to include test and measurement
of acoustic spaces and musical instruments.
A conventional squelch design faces several compromises.
* Squelch too aggressively and audio may be lost.
* Squelch too little and excessive noise may be heard.
* Respond too rapidly and the audio will sound "choppy."
* Respond too sluggishly and entire words or syllables
can be cut off.
SmartSquelch™ achieves an optimal balance of these tradeoffs
by combining several techniques that remove distracting
noise without the squelching action itself becoming a distraction.
The circuitry will perform the following functions:
* Wait for a complete word or syllable before squelching.
* Assess recent squelching history and RF signal
* Assess audio content to determine available masking.
By adjusting squelching behavior dynamically for the optimal
result under varying conditions, the receiver can deliver acceptable
audio quality from otherwise unusable signals.
Microprocessor controlled antenna phase combining
is utilized for diversity reception to keep the receiver
small, yet still deal effectively with multi-path dropouts.
The embedded firmware analyzes RF level, the rate of
change of RF level and the audio content to determine
the optimum timing for phase switching, and the optimum
antenna phase. This adaptive technique operates over a
wide range of RF levels to anticipate dropouts before they
occur. The system also employs "opportunistic switching"
to analyze and then latch the phase in the best position
during brief squelch activity.
With a noise floor at -120 dBV and a frequency response
to 20 kHz, high frequency noise in the source audio is
more apparent than in conventional wireless systems.
The Smart Noise Reduction algorithm works by attenuating
only those portions of the audio signal that fit a statistical
profile for randomness or "electronic hiss." Because
it isn't simply a sophisticated variable low pass filter as
in earlier analog designs, much greater transparency is
obtained. Desired high frequency signals having some
coherence such as speech sibilance and tones are not
The Smart NR algorithm has three modes, selectable
from the front panel LCD. When switched OFF, no noise
reduction is performed. When switched to NORMAL, the
factory default setting, enough noise reduction is applied
to remove most of the hiss from the mic preamp
and some of the hiss from lavaliere microphones. When
switched to FULL, enough noise reduction is applied to
remove most of the hiss from nearly any signal source of
reasonable quality, assuming levels are set correctly at
Analog RF Links
A digitized audio or RF signal occupies a good deal more
bandwidth than the original analog signal. A digital transmission
over the air requires some combination of additional
power, more RF bandwidth and/or compression of
the audio data to achieve adequate operating range and
keep the energy inside the defined spectral mask. Because
of this, digital wireless microphones typically lack
the operating range of conventional FM systems.
With regard to using RF power and spectrum efficiently,
an analog RF link has many advantages in wireless mic
systems, among them long battery life, excellent range,
and the ability to use many systems in close proximity
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) to eliminate squelch
problems in multichannel systems where a pilot tone
signal can appear in the wrong receiver via intermodulation
products. The DSP generated pilot tone also survives
mishandling much better than fragile crystal-based pilot
High Current, Low Noise Amplifiers
The gain stages in the front end use special transistors in
a feedback regulated high current circuit that combines
low noise, low gain, and high power. The design takes all
three of these parameters into consideration at once, to
provide low noise RF amplification, excellent sensitivity
and extremely low susceptibility to intermodulation.
Combining the high power gain stages with the tracking
front end produces a receiver that is immune to single
and multiple interfering signals close to the operating
frequency and in addition, strongly rejects signals that are
much farther away.
Surface Acoustic Wave (SAW) Filter
SAW filters in the first IF section operating at 244 MHz
combine sharp skirts, constant group delay, and wide
bandwidth in one filter. These quartz filters are temperature
stable. This special type of filter allows primary
filtering as early as possible, at as high a frequency as
possible and before high gain is applied to the signal. After
the sharp filtering action of the SAW filters, the signal
is converted to the second IF at 10.7 MHz, then finally to
the third IF at the low frequency of 300 kHz, where the
counting detector generates the audio signal.