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EXB300 - USER AND MAINTENANCE MANUAL - rev.1.1 - 02/02
SOFRATEC BROADCAST EQUIPMENT
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GENERAL DESCRIPTION
The EXB300 is a 300W rated, direct-synthesis, FM-modulated transmitter. Being digitally
controlled,itisextensivelyonfieldprogrammablebyfrontpanelorremotelyineveryrespect:frequency,
power, channel sensitivity, preemphasis, functioning mode (mono, stereo, external mpx), clock and
date and many other parameters without adjusting or substituting any part. A powerful 3-levels
passwordmanagementpermitsaveryhighdegreeofsecurityandprivacyasmayberequiredindifferent
situations. The apparatus requires little o no maintenance and its simple modular layout facilitates stage
testing and servicing.
As imposed by various national standards, these transmitters incorporate sophisticated low-pass
audio filters on mono and stereo channels, and a sharp acting modulation limiter, which is usually set
atapeakdeviationslightlyhigherthan75kHz. Itsinterventionmayneverthelessbeavoided,ifrequired,
pre-setting its threshold at a deviation higher than 150 kHz.
Output frequency is phase-locked to a temperature-compensated crystal oscillator, which
ensures superior precision and stability. A very low noise, low distortion VCO produces a
harmonic-free, spurious-free signal. A lock control circuit inhibits the presence of power on the
output until the apparatus is on the right frequency, when turning on.
Tolowerthenoisethresholdfurther,thelow-frequencyinputsarefittedwithbalancedinputcircuitry.
The input level is precisely adjustable over a broad range, by means of a 0.5dB stepwise variable
attenuators. The transmitter has an auxiliary input, specifically designed for RDS and SCA encoders.
A modulation output permits to control other transmitters or STL's with the same internally processed
high-quality mpx signal.
The alphanumeric display permits easy and accurate metering, adjustment and continuous
monitoring of modulation levels, power, operation and internal parameters. All these information may
beexternallyavailableonthesameRS232I/Oportthatmaybeusedtoremotelycontrolthetransmitter.
In addition to the serial I/O, some signals (RF power, On the air state, Disable line) are available on
a parallel I/O socket for easy interfacing with others analog controllers or supervisory systems.
A top-quality stereo encoder may be factory installed as option and even retrofitted in the field
in a second time, requiring minimum technical skill. The powerful internal software and monitoring
functions recognise its presence and enable its functions.
The RF power amplifier employs a broadband design and has plenty of reserve: the output power
isfeedbackcontrolledforincreasedstabilitytillhigherthannominallevel.Highreflectedpowerislimited
to prevent output stage degradation; direct power is accordingly continuously reduced so as not to
exceed the reflected power safety level. A sturdy telecom-grade high efficiency switch-mode power
supply permits operation in a very wide and noisy mains environment.
The temperature alarm circuitry reduce the output power in case of high internal or ambient
temperature, trying to continue to stay on the air in spite of the adverse conditions.
