XPT/R2G
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8
XPT-2G GENERAL DESCRIPTION
XPT-2G is a FM band broadcasting transmitter with modern conceiving and technology,
which by a simple design produces an output radio signal with high characteristics of quality,
reliability and security.
The simple manufacturing obtained with a high integration of functions, has allowed to
create a machine with few controls and connections. Most printed circuits are multilayer with a
surface mounting technology component assembling. The eventual repairing can be done by simply
changing the fault involved board, without searching the defective component.
One of the most important characteristics is the high quality of the frequency modulation
and the high signal-to-noise ratio; moreover, the modulation is typically constant within 0.5dB
throughout the whole assigned band (typically 10MHz width) .A proper peak detector allows to
perform both traditional modulation measurements (usual bar-graph with peak), and modulation and
power modulation ones with long observation periods (even with many hours or days) according to
the latest international regulations, which properly cared to fix a limit scientifically measurable to
the peak and modulation power (CEPT 54-01).
An particular audio circuit can control the input audio level with a ±6dB dynamics referred
to the nominal value: this can be extremely useful when the audio signal level is not fixed or when
this one can be subject to fluctuations (usually very slow) due to thermal driftsbad systems
maintenance, possible damages along radio link paths etc. A proper board can be inserted to obtain
this function and a proper microprocessor follows constantly the modulation value correcting
through proper algorithms, implemented in its memory, the value of the modulator gain, keeping
this way the modulation very close to the maximum allowed value. The corrections take place at
very long periods of time; the board does not perform the audio compressing-limiting functions, but
just compensates possible drifts occurring on the systems carrying the audio channel before entering
in the FM transmitter. No measurable phase or amplitude distortion is introduced in the modulation
when the automatic gain control circuit is enabled. In addition an alarm which switches the power
off in case of modulation absence can be inserted since the unmodulated carrier transmission is
forbidden in many countries, with no chance to identify the radio.
The transmitter can be set like a modern signals generator so the output power is completely
managed by a device which guarantees that the values of forward power, maximum output power
versus the temperature and loading conditions, are always the ones set or the ones allowed by
maximum limits. A directional wide band coupler with remarkable directivity and large on board
memory allows to obtain a power accuracy worthy of a good measurement instrument.
All parameters (frequency, levels, mono/stereo, pre-emphasis, power) can be set by the
keyboard and stored in E
2
PROM in order to be kept even without electric supply. A great number of
events can be stored: each alarm is distinguished by a starting and an ending alarm date. The
controlled parameters are: modulation absence, heatsink temperature, mains supply voltage, RF
power final stage voltage and current, main oscillator fault.
A second RS232 port placed in the rear part can be connected to a MODEM which is
connected to the phone line thus assuring the transmitter telecontrol, remotely or from the studio.
The transmitter can be modulated by five different audio signal.
The first two ones are made by monophonic left and right channels, which can be balanced
or unbalanced. The input dynamic goes from 0 to +12dBm with an input impedance which can be
