Lectrosonics IFBT5 - Manual (Page 4)

GENERAL TECHNICAL DESCRIPTION
COMPANDOR NOISE REDUCTION
The single band compandor is a high quality audio device that processes the input signal such that the large dy­
namic ranges of input signal can be transmitted to the receiver without overload or noise. A complementary system
in the receiver recovers 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 10dB
signal to noise improvement. Matching de-emphasis is provided in all receivers.
PILOT TONE
The T5/R5 system utilizes an ultrasonic tone modulation of the carrier to operate the receiver squelch. This “pilot
tone” consists of a 29.997kHz signal mixed with the audio signal, just after the compandor, to control the audio
output muting of the receiver. The pilot tone is filtered out of the audio signal immediately after the detector in the
receiver so that it does not influence the compandor or various gain stages.
The basic benefit 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. This is
extremely important in applications that include an automatic microphone mixer.
FREQUENCY AGILITY
The transmitter uses a synthesized, frequency selectable main oscillator. The frequency is extremely stable over a
wide temperature range and over time. Two push-button switches, located on the front panel of the unit, provide 256
frequencies in 100 kHz or 25 kHz steps over a 25.5 MHz range. This alleviates carrier interference problems in
mobile or travelling 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 T5 transmitter operates at 50mW*. The transmitter circuits are buffered and filtered for exceptional spectral
purity. The extra clean signal that results reduces the chances for interference between multiple transmitter installa­
tions.
ANTENNA
At UHF frequencies, where wavelengths and antennas are shorter than at VHF frequencies, a resonant length
antenna is preferred. The antenna on the T5 consists of a flexible 1/4 wavelength bronze cable, detachable via a
BNC
connector.
POWER DELAY
There is a 5 second power on delay to prevent audio thumps when switching from XMIT to TUNE or from TUNE to
OFF. This delay also gives the PLL synthesizer time to fully stabilize. When the transmitter is powered OFF the Pilot
Tone is first turned off muting the audio at the receiver before the rest of the transmitter is powered down preventing
clicks, thumps or feedback from entering the sound system. When switching the power off then back on, always
allow the display to extinguish before switching the power back on.
* May be 10mW depending on destination country.
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