Lectrosonics UM500 - Manual (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
9V
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
5
4
3
2
1
Final
Amplifier
50
Isolator
LF
Roll Off
UM500 Block Diagram
Rio Rancho, NM – USA
5