Lectrosonics IFBT4VHF User Manual

IFBT4-VHF

Synthesized VHF IFB Transmitter

INSTRUCTION MANUAL

Featuring Digital Hybrid Wireless® Technology

U.S. Patent 7,225,135

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Rio Rancho, NM, USA
www.lectrosonics.com

IFBT4-VHF

2

LECTROSONICS, INC.

Table of Contents

General Technical Description ............................................ 4

Introduction .........................................................................4

Audio Input Interface ...........................................................4

Digital Hybrid Wireless® Technology ................................... 5

Audio Signal Processing .....................................................5

Pilot Tone Squelch System .................................................5

Frequency Agility.................................................................5

Power Delay ........................................................................5

Microcontroller ....................................................................5

Transmitter ..........................................................................5

Antenna Port ....................................................................... 5

Front Panel Controls and Functions ...................................6

IFBT4 Front Panel ............................................................... 6

OFF/TUNE/XMIT Switch ..................................................... 6

Power Up Sequence ...........................................................6

Main Window ....................................................................... 6

Frequency Window..............................................................6

Audio Input Gain Window .................................................... 6

Setup Window ..................................................................... 6

COMPAT Setup Screen ....................................................... 7

Lock/Unlock Panel Buttons ................................................. 7

IFBT4 Menu Diagram ..........................................................7

Rear Panel

Controls and Functions ................................................8

IFBT4 Rear Panel ...............................................................8

XLR Jack .............................................................................8

Power Input Connector .......................................................8

Antenna ...............................................................................8

Input Configuration (Mode Switches) .................................. 8

Frequency Selection ............................................................9

Installation and Operation .................................................10

Adjust Audio Input Level ...................................................10

Accessories ........................................................................11

Troubleshooting .................................................................. 12

Specifications .....................................................................13

Service and Repair ............................................................. 14

Returning Units for Repair ................................................14

Synthesized VHF IFB Transmitter

Consumer Alert for US Users - FCC Order DA 10-92

Most users do not need a license to operate this wireless microphone system. Nevertheless,
operating this microphone system without a license is subject to certain restrictions: the system
may not cause harmful interference; it must operate at a low power level (not in excess of 50
milliwatts); and it has no protection from interference received from any other device.

Purchasers should also be aware that the FCC is currently evaluating use of wireless micro­phone systems, and these rules are subject to change. For more information, call the FCC at
1-888- CALL-FCC (TTY: 1-888-TELL-FCC) or visit the FCC’s wireless microphone website
at www.fcc.gov/cgb/wirelessmicrophones. To operate wireless microphone systems at power
greater than 50mW, you must qualify as a Part 74 user and be licensed. If you qualify and wish
to apply for a license go to: http://www.fcc.gov/Forms/Form601/601.html

Rio Rancho, NM

3

IFBT4-VHF

Po
Input
6-18VDC
200mA

XMIT

IFBT4-VHF Transmitter

General Technical Description

Introduction

This version of the IFB “base station” transmitter oper­ates in the television broadcast band from 174 to 216
MHz (US TV channels 7 through 13). It will tune across
the entire band, so clear frequencies can be found
almost anywhere.

The VHF spectrum has not been impacted by the
spectrum auctions and re-packing as much as the
UHF spectrum, so the idea behind this product design
is to operate an IFB system in the VHF band and free
up space for wireless microphones in the UHF band.

The IFBT4 features a graphics type backlit LCD
display with a menu system similar to those provided
on other Lectrosonics receivers. The interface can be
Locked to prevent a user from changing any settings
but still allow browsing of the current settings.

The unit can be powered from any external DC source
of 6 to 18 Volts at 200 mA or from the provided 12 Volt
power supply with a locking power connector. The pow­er inlet has an internal self-resetting fuse and reverse
polarity protection.

The housing is contructed of machined aluminum
extrusion with a durable electrostatic powder coating.
The front and rear panels are machined aluminum with
an anodized finish and laser etched engraving. The
included antenna is a right angle, ¼ wavelength whip
with a BNC connector.

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 mi­crophone inputs, or for high level line inputs, balanced
or unbalanced. The switches also offer special settings
to provide the proper input configurations to match to
Clear Com, RTS1, and RTS2 intercom systems. Pin 1
of the XLR input connector is normally connected to
ground but an internal jumper can be moved if a float­ing input is desired. Phantom supplied microphones
may be connected without the need for DC isolation at
the input of the transmitter.

A user-selectable low frequency roll-off can be set for
35 Hz or 50 Hz as needed to suppress low frequency
acoustic noise or to extend the frequency response.

DSP-controlled Input Limiter

The transmitter employs a digitally-controlled analog
audio limiter prior to the analog-to-digital converter.
The limiter has a range greater than 30 dB 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 keep audio distor­tion low and preserve short term dynamic changes in
the audio.

Block Diagram

Audio Input Interface

XLR

Input

wer

Polyfuse

Connector

2

3

1

Voltage

Regulator

Power

OFF

TUNE

Mode

Set

Switches

(Rear

Panel)

Input

Amplifier

Graphic LCD Display

UP

Front

Panel

DOWN

Controls

MENU

+5 V

+3.3 V

+1.8 V

+15 V

-15 V

Shunt

Limiter

Roll-Off

Phase Locked Loop

11.3 MHz
Reference

Audio
Level

Audio

Input
Amp

LF

4

A-D

Converter

11001001 11001001

Digital Signal Processor

Microprocessor

D-A

Converter

Voltage

Controlled

Oscillator

Filter
Amp

11.3 MHz
Reference

Final

Amplifier

LECTROSONICS, INC.

Synthesized VHF IFB Transmitter

Digital Hybrid Wireless® Technology

The design is based upon the patented Lectrosonics
Digital Hybrid Wireless® system.* While at the time of
the first release of the product, there is only a compan­ion analog receiver, the Digital Hybrid Wireless system
is included for compatibility with future products.

Audio Signal Processing

Lectrosonics IFB systems use a single band compan­dor and pre-emphasis/de-emphasis to reduce noise.
This signal processing is generated and applied by the
DSP for accuracy and clean handling of signal dynam­ics.

The DSP also provides the ability to employ compat­ibility modes for use with other wireless equipment in
the VHF spectrum that may come along in the future.

Pilot Tone Squelch System

Lectrosonics IFB systems use a supersonic “pilot
tone” to control the squelch activity in the receiver. A
valid RF signal will include the pilot to signal the audio
output to open. Even strong interference on the same
frequency cannot open the audio output if the pilot
tone is not present.

During normal operation, an IFB receiver will listen for
the distinctive pilot tone, remaining silent (squelched)
until the pilot tone is detected. The pilot tone is located
well above audio frequencies and is never passed
through to the receiver’s audio output.

Power Delay

When powering the transmitter on and off, and when
switching between the XMIT and TUNE modes, intel­ligent circuitry adds brief delays in order to allow time
for circuits to stabilize, both locally and in the match­ing receiver. These delays prevent clicks, thumps and
other noise in the audio.

Microcontroller

The microcontroller oversees most system operations,
including RF frequency and output, DSP audio func­tions, buttons and display, and more. User settings are
stored in non-volatile memory, so they are retained
even when the power is turned off.

Transmitter

The transmitter operates at the maximum allowed RF
power level to ensure a clean signal free of dropouts
and noise. All transmitter circuits are buffered and
filtered for excellent spectral purity. The clean trans­mitted signal reduces the chances for interference in
multiple transmitter installations.

Antenna Port

The 50 Ohm BNC output connector will work with stan­dard coaxial cabling and remote antennas.

Frequency Agility

The IFBT4 transmitter uses a synthesized, frequency
selectable main oscillator. The frequency is extremely
stable over a wide temperature range and over time.
The transmitter’s standard tuning range covers 239
frequencies from 174 to 216 MHz in 175 kHz steps. to
alleviate interference problems in mobile applications.

Rio Rancho, NM

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