Lectrosonics UM500 User Manual download pdf (Page 5)

Frequency-Agile UHF Belt-Pack Transmitter

INPUT LIMITER

The 500 series transmitters employ a digitally-controlled analog audio limiter just before the analog-to-digital con-

verter. The limiter has a range of more than 30dB for excellent overload protection. A dual release envelope makes

the limiter acoustically transparent while maintaining low distortion. It can be thought of as two limiters in series,

connected as a fast attack and release limiter followed by a slow attack and release limiter. The limiter recovers

quickly from brief transients, so that its action is hidden from the listener, but recovers slowly from sustained high

levels, to both keep audio distortion low and preserve short term dynamic changes.

Generally speaking, some limiting is desirable in normal operation to improve the signal to noise ratio of the system.

The limiting action is not audible and does not create distortion. A highly trained ear would hear only the compres-

sion of the peaks in the audio signal, which is desirable with most recorders and many sound reinforcement systems.

LONG BATTERY LIFE

Switching power supplies throughout the design allow over 6 hours of operation using a single 9 Volt alkaline battery.

(A 9V lithium battery will provide over 13 hours of operation.) The battery contacts are spring loaded to prevent

“rattle” as the unit is handled.

FREQUENCY AGILITY

The transmitter section uses a synthesized, frequency selectable main oscillator. The frequency is extremely stable

over a wide temperature range and over time.

Two rotary switches, located on the side panel of the unit, provide 256 frequencies in 100kHz or 25kHz steps over a

25.5MHz range. The 100kHz / 25kHz step choice is programmable by an authorized service center. The large

number of frequencies available alleviates carrier interference problems in mobile or traveling applications.

ANTENNA

The antenna on the UM500 consists of a flexible 1/4 wavelength bronze cable, detachable via an SMA connector.

The impedance of this connector is 50 Ohms.

+5V Bias

Phase Locked Loop

Voltage

Controlled

Oscillator

Freq

Switches

11001001

A-D

Converter

Digital Signal Processor

11001001

D-A

Converter

Shunt

Limiter

Bicolor

Modulation

LEDs

Microprocessor

Battery

Switching

Power

Supply

+5v

+1.8v

+9v

-3v

Hi/Lo

Pass

Filter

Audio

Encoded

Audio +

Pilot Tone

4MHz

Reference

Bicolor

Power

LED

Mic

Jack

Supply

Audio

Level

Input

Amp

Final

Amplifier

Isolator

Roll Off

UM500 Block Diagram

Rio Rancho, NM – USA

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Lectrosonics UM500 User Manual Page 5

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