Digital Hybrid Wireless Technology; Audio Signal Processing; Pilot Tone Squelch System; Frequency Agility - Lectronics IFBT4/E01-VHF Instruction Manual

Digital Hybrid Wireless
Conventional analog systems use compandors for
enhanced dynamic range, at the cost of subtle artifacts
(known as "pumping" and "breathing"). Wholly digital sys-
tems defeat the noise by sending the audio information
in digital form, at the cost of some combination of power,
bandwidth and resistance to interference.
Lectrosonics Digital Hybrid Wireless
come channel noise in a dramatically new way, digitally
encoding the audio in the transmitter and decoding it
in the receiver, yet still sending the encoded informa-
tion via an analog FM wireless link. This proprietary
algorithm is not a digital implementation of an analog
compandor but a technique that can be accomplished
only in the digital domain, even though the inputs and
outputs are analog.
Channel noise still impacts received signal quality and
will eventually overwhelm a receiver. Digital Hybrid
®
Wireless simply encodes the signal to use a noisy
channel as efficiently and robustly as possible, yield-
ing audio performance that rivals that of wholly digital
systems, without the power and bandwidth problems
inherent in digital transmission.
Because it uses an analog FM link, Digital Hybrid
®
Wireless enjoys all the benefits of conventional FM
wireless systems, such as excellent range, efficient
use of RF spectrum, and resistance to interference.
However, unlike conventional FM systems, it does
away with the analog compandor and its artifacts.

Audio Signal Processing

Lectrosonics IFB systems use a single band compan-
dor 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 dynam-
ics.
The DSP also provides the ability to employ compat-
ibility 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.
Rio Rancho, NM
®
Technology
®
systems over-
Synthesized VHF IFB Transmitter

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.

Power Delay

When powering the transmitter on and off, and when
switching between the XMIT and TUNE modes, intel-
ligent circuitry adds brief delays in order to allow time
for circuits to stabilize, both locally and in the match-
ing 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 func-
tions, 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 trans-
mitted signal reduces the chances for interference in
multiple transmitter installations.

Antenna Port

The 50 Ohm BNC output connector will work with stan-
dard coaxial cabling and remote antennas.
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