Lectrosonics UCR511 User Manual download pdf (Page 6)

UCR511

(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 down to 10.7 MHz, filtered through

two ceramic filters for sharp selectivity, then converted to

300 kHz.

DIGITAL PULSE COUNTING DETECTOR

The UCR511 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

Note

The above description applies only in 500 Series mode. In 300

Series mode, only one pilot tone frequency is used on all channels,

emulating the original crystal-based system. In other compatibility

modes, no pilot tone is used.

The 500 Series system design uses a DSP generated

ultrasonic pilot tone to control the receiver audio muting

(squelch). Brief delays (preset into the UCR511 cir-

cuitry) eliminate thumps, pops or other transients that

can occur when thewhen the associated 500 Series

transmitter is turned 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.

SMART SQUELCH

™

The UCR511 employs a sophisticated squelching system

in an attempt to deliver the cleanest possible audio

during marginal conditions of reception. Any squelching

system faces inevitable trade-offs: squelch too much and

valuable audio information may be lost, squelch too little

and excessive noise may be heard; respond too rapidly

and the audio sounds “choppy,” respond too sluggishly

and syllables or entire words can be cut off.

The UCR511 combines several techniques to achieve an

optimal balance, removing distracting noise, without the

squelching action itself becoming a distraction. One of

these techniques involves waiting for a word or syllable

to complete before squelching. Another incorporates

recent squelching history and recent signal strength,

adjusting squelching behavior dynamically for the most

serviceable result under variable conditions. Using these

and other techniques, the UCR511 can deliver accept-

able audio quality from otherwise unusable signals.

In the Pilot Tone Bypass mode, the squelch system is

disabled. Received audio remains unmuted at all times

with this setting. (See Front Panel Controls and Func-

tions.)

SMART NOISE REDUCTION (SmartNR

™

)

Note

The SmartNR setting is user selectable only in 500 Series 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 UCR511 has been meticulously designed using the

best available low noise components and techniques.

Nonetheless, the wide dynamic range of digital hybrid

technology, 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

microphone itself. (To put this in perspective, the noise

generated by the recommended 4 k Ohm bias resistor of

many electret lavaliere mics is –119 dBV and the noise

level of the microphone’s electronics is much higher.) In

order to reduce this noise and thus increase the effective

dynamic range of the system, the UCR511 is equipped

with a Smart Noise Reduction algorithm, which removes

hiss without sacrificing high frequency response.

The Smart Noise Reduction algorithm works by attenuat-

ing only those portions of the audio signal that fit a

statistical profile for randomness or “electronic hiss”.

Because it isn’t simply the same sophisticated variable

low pass filter as in Lectrosonics’s 300 Series designs,

much greater transparency is thus obtained. Desired

high frequency signals having some coherence such as

speech sibilance and tones are not affected.

The Smart Noise Reduction algorithm has three modes,

selectable from a user setup screen - OFF/NORMAL/

FULL.

OFF, no noise reduction is performed and

complete transparency is preserved. All signals

presented to the transmitter’s analog front end,

including any faint microphone hiss, will be

faithfully reproduced at the receiver.

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. The noise reduction

benefit is dramatic in this position, yet the degree

of transparency maintained is exceptional.

FULL, enough noise reduction is applied to

remove most of the hiss from nearly any signal

source of reasonable quality, assuming levels are

set properly at the transmitter. This additional

noise reduction comes at the cost of some

transparency for low-level room noise, yet the

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