General Technical Description; Introduction; Audio Input Interface; Input Limiter - Lectrosonics IFBT4/X Instruction Manual

IFBT4, IFBT4/E01, IFBT4/X

General Technical Description

Introduction

The IFBT4 IFB transmitter brings DSP capability and a
convenient LCD interface to the popular Lectrosonics
IFB product line. Replacing the venerable IFBT1 trans-
mitter, the IFBT4 retains the same physical size and is
fully interchangeable with its predecessor in terms of
audio, RF and power interfaces. Along with providing
peerless audio quality with wide frequency response
and dynamic range in Nu Hybrid mode, the technol-
ogy used in the IFBT4 includes compatibility modes for
Lectrosonics Mode 3 and IFB receivers.
The IFBT4 features a graphics type backlit LCD display
with a menu system similar to those featured in our 400
Series receivers. The IFBT4 can be "Locked" to prevent
a user from changing any settings but still allow brows-
ing of the current settings.
The IFBT4 can be powered from any external DC
source of 6 to 18 Volts at 200 milliamps maximum or
from the provided 12 Volt power supply with a locking
power connector. The unit has an internal self-resetting
fuse and reverse polarity protection.
The IFBT4 is housed in a machined aluminum case
with a tough electrostatic powder coating. The front and
rear panels are anodized aluminum with laser etched
engraving. The included antenna is a right angle, ¼
wavelength monopole with a BNC connector, construct-
ed of polymer coated flexible steel cable.
These features, along with the 250 milliwatt RF output
and a wide range of selectable audio input types and
levels, make the IFBT4 an excellent choice for long
range IFB applications and other long range wireless
audio needs.
XLR
Input
Connector
2
3
1
Power
+
Input
Voltage
6-18VDC
-
Regulator
200mA
Polyfuse
Power
OFF
TUNE
XMIT
4

Audio Input Interface

Mode
Set
Input
Switches
Amplifier
(Rear
Panel)
Roll-Off
Shunt
Limiter
Graphic LCD Display
UP
Front
Panel
DOWN
Controls
MENU
+5 V
11.3 MHz
Reference
+3.3 V
+1.8 V
-5 V
Audio Input Interface
The standard 3 pin XLR connector on the rear panel
handles all audio inputs. The four DIP switches allow
setting the input sensitivity for low levels, such as micro-
phone inputs, or for high levels, such as line inputs, bal-
anced or unbalanced. The switches also offer special
settings to provide the proper input configurations to
match to Clear Com, RTS1, and RTS2 intercom sys-
tems. Pin 1 of the XLR input connector is normally con-
nected to ground but an internal jumper can be moved if
a floating input is desired.
While the XLR input does not offer phantom power, it is
fully compatible with standard 48 Volt phantom power.
Phantom supplied microphones may be connected to
the IFBT4 without the need for DC isolation.
A user-selectable low frequency roll-off can be set for
35 Hz or 50 Hz. The recommended 50 Hz default set-
ting helps to remove wind and traffic noise, air con-
ditioner rumble, and other sources of undesired low
frequency audio. The 35 Hz setting offers a fuller range
of sound in the absence of adverse conditions.

Input Limiter

A DSP-controlled analog audio limiter is employed
before the analog-to-digital converter. The limiter has a
range of more than 30 dB for excellent overload protec-
tion. A dual release envelope makes the limiter acousti-
cally transparent while maintaining low distortion. It can
be thought of as two limiters in series: a fast attack and
IFBT4 Transmitter
Block Diagram
A-D
Converter
Audio
Input
Amp
11001001
LF Audio
Level
Digital Signal Processor
Microprocessor
Phase Locked Loop
D-A
Converter
Filter
Amp
11001001
11.3 MHz
Reference
Isolator
Voltage Final 50
Amplifier
Controlled
Oscillator
LECTROSONICS, INC.