Input Limiter; Long Battery Life; Frequency Agility; Antenna - Lectrosonics UM500 Operating Instructions Manual

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
Mic
Supply
Jack
1
Hi/Lo
2
Pass
3
4
Filter
5
Shunt
Limiter
Bicolor
Modulation
LEDs
Phase Locked Loop
4MHz
Reference
A-D
Audio
Input Converter
Amp
Audio
LF
Level
11001001
Roll Off
Microprocessor
Freq
Switches
Rio Rancho, NM – USA
Frequency-Agile UHF Belt-Pack Transmitter
D-A
Converter
11001001
Digital Signal Processor
Voltage
Controlled
Oscillator
UM500 Block Diagram
Encoded
Audio +
Pilot Tone
Switching
Power
9V
Supply
Battery
Bicolor
Power
LED
Isolator
50
Final
Amplifier
+5v
+1.8v
+9v
-3v
5