TEM A07A2200S, Maintenance And Installation Manual

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A07A2200S
The mono signal or the stereo one, thus obtained, is combined with the other three possible
input audio signals: an external Multiplex signal and two SCA signals, one of which can be the
RDS one, which can be synchronized with a 19KHz one connected on the IN/OUT rear connector.
The composite signal can enter the AGC board, which has the task to check the its amplitude
and consequently to keep the modulation at the correct value, or it can follow its path and enter into
the frequency modulator after having passed through a limiter circuit (CLIPPER). This circuit must
became active just in cases of faults of previous circuits or in case of mistake in the setting of the
low frequency input nominal levels; this is to avoid to interfere with the adjacent channels. For not
activating this “fuse”, which produces remarkable distortions on the modulation, it is necessary to
take all proper cautions, that is the use of external compressor-limiters or by inserting the internal
AGC circuit which protects a lot against damages and drifts.
The oscillator, directly modulated by the composite signal, covers the whole FM band and
it’s synthesized in steps of 10KHz . The reference frequency is obtained by a 10MHz crystal kept at
constant temperature of 55°C, whilst the output frequency is set by the main microcontroller. The
oscillator phase noise is very good and it is in compliance with ETSI 300-384 regulations (<­
145dBc for a shifting of 1MHz from the carrier). The modulation linearity is typically contained
within 0.1dB without complicated corrections.
The RF final power circuit is wide band and it provides 2000W RF output controlled with
high accuracy; directional coupler has a directivity higher than 25dB on the whole band and an error
which is lower than 0.2dB, it is also compensated in temperature and totally shielded.
The power supply is of a switching type and it gives the four essential voltages, all obtained
with this technique. A small voltage measurement transformer allows to check the effective value of
mains supply voltage with accuracy and to interrupt the output power in case this value exits from
the normal operating window of the transmitter (10% respect the nominal value of 230V
AC
). The
mechanical position of the power supply and the final circuits of RF power allow to obtain a vent
flu just for cooling of the involved circuits, obtaining this way a really remarkable efficiency of that
function. In normal running conditions, when the transmitter is working in a full power at
environmental temperature, the radiator temperature is lower than 40°C, whereas the other circuits
temperature does not exceed 30°C. No components are involved with the air flow, in any case there
is a filter on the aspiration fan. The power supply is completely shielded both for internal circuits
and for its unavoidable emissions toward the outside.
Data displaying and setting is obtained by a board which is placed directly on the front panel
containing a microprocessor, memory, keyboard, LCD display. The displaying area is wide so
allowing to display and set needed data in a very easy way, thus making the transmitter-user
technician interaction extremely user friendly.
It’s possible to protect the transmitter input and output parameter settings with a password,
while all measurements can be done by whoever without interfering on its operation.
Two communication RS232 ports and a RS485 port can make possible the communication
between the transmitter and a PC, with the power amplifier and the driver exciter, or with a modem
connected with the telephone line.
Maintenance or repairing of damages do not require the soldering use for the replacement of
the parts to be changed; only six flat cables link all different boards.
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