T.E.M. A07B500S, Руководство пользователя

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A07B500S manual
Pag. 11
GENERAL DESCRIPTION
3.1 Main features
A07B500S 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 hi 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 done by the high quality of the frequency
modulation and the high signal-to-noise ratio; moreover, the modulation is typically constant within
0.1dB throughout the whole FM band (88–108MHz ). 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, reflected 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.