Lectrosonics IFBT4M, IFBT4V, IFBT4L, IFBT4H Users Manual
T4
Multi-Frequency IFB Transmitter
INSTRUCTION MANUAL
Featuring Digital Hybrid Wireless™ Technology
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Rio Rancho, NM, USA
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T4
2
LECTROSONICS, INC.
Multi-Frequency IFB Transmitter
Table of Contents
Introduction .............................................................................................................................................................................................4
General Technical Description ..............................................................................................................................................................5
Audio Input Interface .............................................................................................................................................................................5
Audio Processor ....................................................................................................................................................................................5
Compandor Noise Reduction ................................................................................................................................................................5
T4 IFB Transmitter Block Diagram ........................................................................................................................................................5
Pilot Tone ..............................................................................................................................................................................................6
Frequency Synthesizer .........................................................................................................................................................................6
Power Delay ..........................................................................................................................................................................................6
Microcontroller ......................................................................................................................................................................................6
Transmitter ............................................................................................................................................................................................6
Antenna System ....................................................................................................................................................................................6
Front Panel Controls and Functions .....................................................................................................................................................7
T4 Front Panel ......................................................................................................................................................................................7
OFF/TUNE/XMIT Switch .......................................................................................................................................................................7
Power Up Sequence .............................................................................................................................................................................7
LCD Display ..........................................................................................................................................................................................7
Freq Buttons (Up and Down) ................................................................................................................................................................7
Audio Level Control ...............................................................................................................................................................................7
Rear Panel Controls and Functions ......................................................................................................................................................8
T4 Rear Panel .......................................................................................................................................................................................8
XLR Jack ...............................................................................................................................................................................................8
Mode Switches ......................................................................................................................................................................................8
12 VDC (Power Input Connector) ..........................................................................................................................................................8
Antenna .................................................................................................................................................................................................8
Installation and Operation .....................................................................................................................................................................9
Operating Notes ....................................................................................................................................................................................10
Accessories ..........................................................................................................................................................................................10
Troubleshooting ....................................................................................................................................................................................11
Frequency Blocks and Ranges ...........................................................................................................................................................12
Specifi cations .......................................................................................................................................................................................13
Service and Repair ...............................................................................................................................................................................14
Returning Units for Repair ..................................................................................................................................................................14
Introduction
Thank you for selecting the Lectrosonics frequency
agile, narrowband, T4 IFB (Interruptible Foldback) transmitter. The T4 is the result of over 100 years of engineering experience with the very latest components, in
a design that addresses the most demanding professional applications.
The Lectrosonics T4 IFB Transmitter along with the
companion R1 or R1a IFB Receivers allow on-air talent
to monitor program audio and receive cues from directors and other production personnel.
The T4 IFB Transmitter is a rugged, machined aluminum package. The input section is adjustable for
virtually any microphone or line level audio source. The
antenna is a detachable, locking 1/4 wavelength fl exible
bronze cable that connects to a 50 Ohm BNC connector
on the transmitter.
Only the T4 IFB Transmitter is covered in this manual.
Companion receivers are covered in separate manuals.
The T4 IFB Transmitter will operate with any Lectrosonics R1 or R1a IFB Receiver in the same frequency
group.
The T4 is also compatable with the Lectrosonics 100
Series, 200 Series, and 400 Series receivers as well as
several other brand systems.
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T4
General Technical Description
The T4 IFB Transmitter is comprised of a number of
functional subsystems, including Audio Input Interface,
DSP Audio Processor and Pilot Tone, Frequency Synthesizer, Microcontroller, Transmitter, Antenna System
and Power Supply. (See block diagram.)
The T4 is designed to operate primarily with the Lectrosonics R1 and R1A IFB receivers, and is also capabable of operating with the Lectrosonics 100 Series, 200
Series, 400 Series receivers. The T4 features microprocessor control of 256 operating frequencies within
any one of at least nine UHF frequency bands and the
944MHz band.
The T4 uses 20 kHz deviation in the IFB and 100 series
modes for an effi cient use of bandwidth. The 200
Series and 400 Series modes use 75kHz bandwidth for
high signal to noise ratio. The transmitter circuits are all
regulated for frequency stability and high audio performance. The input amplifi er is a discreet differential
circuit which can be adjusted to allow the use of many
different input sources with robust overload capability
without clipping.
Audio Input Interface
The input sensitivity and XLR pin functions can be customized using a DIP switch located on the back panel.
Different combinations of gain and input confi gurations
are possible without rewiring the mic connector. Pin
1 of the XLR input connector is normally connected
directly to ground but an internal jumper can be moved
if a fl oating input is desired.
The Audio (+) and (–) are “dry” inputs and can each
withstand +/- 50 VDC.
Audio DSP and Noise Reduction
The original Lectrosonics IFB system was designed
with single band compand ing which is an audio device
that processes (compresses) the input signal so that
the large dynamic ranges of the input signals can be
transmitted to the receiver without overload or noise. A
complementary system in the receiver recovers (decompresses) the original dynamics of the signal for full
audio quality. Compression and expansion ratios are
complementary at 2:1. High frequency pre-emphasis is
implemented in the transmitter to provide another 10 dB
signal to noise improvement. Matching de-emphasis is
provided in all receivers.
The IFBT4 is designed with Audio Digital Signal Processor algorithms that digitally emulate the original compandor circuits in order to maintain compatability with
the IFBR1/IFBR1a, 100 Series, and 200 Series receivers using the same analog FM links. This same DSP
circuitry also provides an algorithm compatible with
the Lectosonics Digital Hybrid Wireless™ 400 Series
systems and eliminates the need for pre-emphasis and
de-emphasis.
T4 IFB Transmitter Block Diagram
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LECTROSONICS, INC.
Multi-Frequency IFB Transmitter
Pilot Tone
The T4/R1A system uses an ultrasonic tone modulation of the carrier to operate the receiver squelch. This
“pilot tone” consists of a 29.997 kHz signal in the DSP
and is mixed with the audio signal to the FM modulator.
The pilot tone controls the audio output muting of the
receiver and is fi ltered out of the audio signal immediately after the detector in the receiver so that it does not
infl uence the compandor or various gain stages.
The benefi t of the pilot tone squelch system is that the
receiver will remain muted until it receives the pilot tone
from the matching transmitter, even if a strong RF signal is present on the carrier frequency of the system.
The T4 DSP also generates pilot tones to operate with
the 200 Series and 400 Series receivers as well as
several other popular system receivers.
Frequency Synthesizer
The transmitter uses a synthesized, frequency selectable main oscillator. The frequency is extremely stable
over a wide temperature range and over time. The
push-button switches, located on the front panel of the
unit, provides the user access to set 256 frequencies in
100 kHz steps over a 25.5 MHz range. This signifi cantly
alleviates carrier interference problems in mobile or
traveling applications.
Microcontroller
Frequency adjustment and display are handled by
the microprocessor. Nonvolatile memory is provided
for holding the last frequency used, even if power is
removed from the unit for any length of time. Each time
the transmitter is powered up, it will display the last
frequency used.
Transmitter
The T4 transmitter operates at 250 mW, more powerful than most IFB systems on the market today. The
higher power ensures a clean signal free of dropouts
and noise. The transmitter circuits are buffered and
fi ltered for exceptional spectral purity. The extra clean
signal that results reduces the chances for interference
between multiple transmitter installations.
Antenna System
The antenna on the T4 consists of a fl exible 1/4 wavelength bronze cable, detachable via a BNC connector.
The 50 ohm output connector works conveniently with a
variety of remote antennas for installation in studios and
production trucks & vans.
Power Delay
There is a fi ve second power-ON/OFF delay to prevent
audio thumps when switching from XMIT to TUNE or
from TUNE to OFF. This delay also gives the Frequency
Synthesizer time to fully stabilize. When the transmitter
is powered OFF, the Pilot Tone is fi rst turned off muting
the audio at the receiver before the rest of the transmitter is powered down. This prevents clicks, thumps or
feedback from entering the sound system.
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