User's Manual

Compact Portable Receiver
Rio Rancho, NM
5
SmartSquelch
™
A DSP-based algorithm named SmartSquelch
TM
optimiz-
es the receiver performance in very weak signal condi-
tions. The RF level and supersonic noise in the audio
are continuously monitored to determine the appropriate
noise reduction needed and the point at which squelch
(complete muting of the audio) is necessary.
As the RF level decreases and supersonic noise in the
signal begins to increase, a variable knee, high frequency
roll-off filter is applied to suppress high frequency noise.
The filtering action moves in and out smoothly to avoid
abrupt changes that could be audible. When the RF
signal becomes so weak that the receiver can no longer
deliver usable audio, the squelch will activate.
SmartDiversity
™
Microprocessor controlled antenna phase combining
is used for diversity reception. The 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. The system
also employs “opportunistic switching” to analyze and
then latch the phase in the best position during brief
squelch activity.
Turn On and Turn Off Delays
A brief delay is applied when the receiver is powered
up or down to prevent audible noise such as a thump,
pop, click or other transient noise.
Test Tone
To assist in matching the audio levels of equipment
connected to the receiver, a 1 kHz audio test tone gen-
erator is provided, with an output level adjustable from
-50 to +5 dBu in 1 dB increments.
The tone simulates the audio output with a steady sig-
nal at full modulation, making it easy to adjust the level
to precisely match the optimal level for the connected
device and maximize the signal to noise ratio of the
system.
LCD Display
Setup and monitoring is done through the LCD display
on the control panel. The LCD image can be inverted
as desired for personal preference or maximum vis-
ibility in direct sunlight. The built-in backlight for viewing
in dimly lit environments can be set to remain on for 30
seconds, 5 minutes or to remain on constantly.
Smart Noise Reduction (SmartNR
™
)
Note: The SmartNR setting is user selectable
only in the Digital Hybrid compatibility mode. In
other modes, noise reduction is applied in such a
way as to emulate the original analog system as
accurately as possible and is not user adjustable.
The wide dynamic range of digital hybrid technol-
ogy, combined with flat response to 20 kHz, makes it
possible to hear the -120 dBV noise floor in the mic
preamp, or the (usually) greater noise from the mi-
crophone itself. To put this in perspective, the noise
generated by the recommended 4k bias resistor of
many electret lavaliere mics is –119 dBV and the noise
level of the microphone’s electronics is even higher. In
order to reduce this noise the receiver is equipped with
a “smart” noise reduction algorithm called SmartNR
®
,
which removes hiss without sacrificing audio high
frequency response.
SmartNR
®
works by attenuating only those portions of
the audio signal that fit a statistical profile for random-
ness or “electronic hiss.” Because it is much more than
a sophisticated variable low pass filter, the transpar-
ency of the audio signal is preserved. Desired high
frequency signals having some coherence are not
affected, such as speech sibilance and tones.
The Smart Noise Reduction algorithm has three
modes, selectable from a user setup screen. The
optimal setting for each application is subjective and is
normally selected while simply listening.
• OFF defeats noise reduction and complete trans-
parency is preserved. All signals presented to the
transmitter’s analog front end, including any faint
microphone hiss, will be faithfully reproduced at
the receiver output.
• NORMAL applies enough noise reduction to
remove most of the hiss from the microphone
preamp and some of the hiss from lavaliere micro-
phones. The noise reduction benefit is significant
in this position, yet the degree of transparency
maintained is exceptional.
• FULL applies enough noise reduction to remove
most of the hiss from nearly any signal source of
reasonable quality and some high frequency en-
vironmental noise, assuming the input gain is set
properly at the transmitter.