Lectrosonics UT700 User Manual download pdf (Page 6)

UDR700 / UM700 / UT700

The 244 MHz from the first IF is reduced to the second

IF of 10.7 MHz, and is then fed to the Quadrature

Detector. The first mixer is a GaAs MMIC device with a

rated IP3 (third order intercept) of +24 dBm to minimize

undesired IM products. Because the signal is digital,

thermal drift in the detector has little effect on the

signal’s content, unlike an analog receiver.

Digital Demodulator

The digital demodulator consists of a PLL clock recov-

ery circuit and a bit slicer. The recovered bit clock and

data stream are fed to the DSP. In addition, the recov-

ered bit clock is used to derive the timings for the

receiver’s digital audio circuits, so the receiver audio is

synchronous with the transmitter audio, sample for

sample.

Digital Signal Processing

The DSP uses the packet headers as a timing refer-

ence to recover the digital audio data. The data is then

decrypted and decoded to recover the original digitized

audio samples. Additionally, the packet headers also

contain transmitter battery status information, which is

extracted by the DSP.

Audio Output

The digital audio samples are sent to the AES-3id

transmitter for digital audio output, and to the D/A

converter for conversion to analog. The converter

output is filtered and amplified, and then fed to a

transformer, attenuator and XLR jack. The analog

output is also sent to a separate headphone amplifier

on the UCR700 front panel for monitoring purposes.

The signal at the headphone output is taken just ahead

of the output transformer, so it provides the same audio

quality as the XLR output and can also be used as a

second output or recorder feed.

UM700 Block Diagram

The main audio output amplifier is set for maximum

gain. This output passes through a passive attenuator

and phase switch on its way to the rear panel Audio

Output XLR jack. The passive attenuator reduces the

audio level in calibrated 5 dB steps, ensuring the signal-

to-noise ratio of the receiver remains the same at all

output levels selected by the rear panel control.

Encrypted Digital Transmitters

Two encrypted digital transmitters are offered, a belt

pack unit and a hand held unit. Although their physical

packages differ, internally, they are essentially the

same. The major difference is the microphone input

jack in the UM700 and the VariMic

™

used in the UT700

hand held transmitter.

The microphone input jack used in the UM700 is

configured so that virtually every lavaliere, hand-held or

shotgun mic can be used, regardless of whether they

use positive or negative bias. (See UM700 Controls

and Functions and 5-Pin Input Jack Wiring.)

The UT700 uses a built in microphone element. (See

UT700 Microphone Element.)

DSP-Cntrolled Dual Envelope Analog Limiter

In order to make the best use of the high quality A/D

converter, microphone audio is limited in the analog

domain first, before being sampled. The DSP controls

this process, but because the limiting is done in the

analog domain, levels near the converter’s maximum

may be used without fear of clipping. (The limiter has a

range of more than 30 dB for excellent overload protec-

tion.)

The limiter has a fast attack, but different release

characteristics, depending on the nature of the signal

that drove the input into limiting. Brief transients result

in a fast decay, to avoid “pumping” effects, while sus-

tained loud signals result in a slower decay, to keep

distortion to a minimum. The result is a transparent-

sounding limiter with excellent low distortion character-

istics.

Phase

Locked

Loop

Freq

Switches

11001001

A-D

Converter

Digital Signal Processor

Shunt

Limiter

Bicolor

Modulation

LEDs

Microprocessor

Battery

Switching

Power

Supply

+3.3v

+1.8v

+9v

-3v

Isolator

Hi/Lo

Pass

Filter

Audio

Bicolor

Power

LED

Audio

Level

Input

Amp

Rolloff

Digital

Modulator

Amp

+3.3V Bias

Supply

Mic

Jack

Dual

Envelope

Limiter

Encode

Encrypt

Voltage

Controlled

Oscillator

Encryption

Key Link

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Lectrosonics UT700 User Manual Page 6

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