Lectrosonics T1 - Manual (Page 5)

Multi-Frequency IFB Transmitter
General Technical Description
The T1 IFB Transmitter is comprised of a number of
functional subsystems, including Audio Input Interface,
Audio Processor, Pilot Tone, Frequency Synthesizer,
Microcontroller, Transmitter, Antenna System and
Power Supply. (See block diagram.)
The T1 is designed to operate with the Lectrosonics R1
and R1A IFB receivers, and Lectrosonics R400A
receivers, and features microprocessor control of 256
operating frequencies within any one of at least nine
frequency bands.
The T1 uses 20 kHz deviation for an efficient use of
bandwidth. The transmitter circuits are all regulated for
frequency stability and high audio performance. The
input amplifier is a discreet differential circuit which can
be adjusted to allow the use of many different input
sources.
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 configu­
rations 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 floating input is desired.
The Audio (+) and (–) are “dry” inputs and can each
withstand +/- 50 VDC.
T1 IFB Transmitter Block Diagram
Warning: Direct connection to a phone line can
damage the transmitter’s inputs.
Audio Processor
The Audio Processor section has several functions,
including signal limiting, filtering and companding
(dynamic range compression). Audio limiting is accom­
plished by a Shunt Limiter placed before the filter and
compandor circuits. A Bandpass Filter limits the audio
bandwidth to 100 Hz at the low end and 10 kHz in the
upper range. The single band compandor circuit
compresses the dynamic range of the audio signal and
prepares it for transmission. It is one half of a system
that requires a matching receiver to decode the signal
and restore its original dynamic range.
Compandor Noise Reduction
The single band compandor is a high quality 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.
T1 IFB Transmitter
Block Diagram
Rio Rancho, NM 5