EuroTel ETL0W474G, Руководство по эксплуатации и техническому обслуживанию

Страница: 11 / 39

Rev. 004 ETL0W474G
IV - IV - IV - IV - FUNCTIONAL DESCRIPTION FUNCTIONAL DESCRIPTION FUNCTIONAL DESCRIPTION FUNCTIONAL DESCRIPTION
1 ) 1 ) 1 ) 1 ) Theory of operation of UHF RF Amplifier ETL0W474G series Theory of operation of UHF RF Amplifier ETL0W474G series Theory of operation of UHF RF Amplifier ETL0W474G series Theory of operation of UHF RF Amplifier ETL0W474G series
•
The series ETL0W474G UHF TV RF Amplifier blocks diagram is shown in Figure 1.
•
The nominal RF input coming from the external Exciter is pre-amplified by the driver module
MOE267. An electronic attenuator is mounted at the input of the driver amplifier. The MLC signal
coming from Logic & Microprocessor board controls the attenuator, in order to equalize the gain of
the modular amplifiers of the system.
•
On module ETL0W474G an ALC control signal manages the output power of the amplifier in order
to keep constant its value. This ALC reference level is set directly on the module via the control
button on the front panel. When the transmitter system has more than one ETL0W474G Amplifier,
the ALC reference is provided by the Supervisor.
•
A directional coupler monitors forward input power sent to the final stage. D.C. samples of these
quantities are sent to the metering, alarm and protection module.
A four way hybrid divider splits the drive power into four components, which feed four modules
MOE272. RF output from each module is combined by a four way hybrid combiner.
The output directional coupler, which is equipped with built-in high sensitivity detectors for forward
and reflected RF power, provides D.C. samples to the Metering and Protection module.
•
The metering outputs of the metering, alarm and protection module feed an alphanumeric display,
located on the front panel. This display provides all the significant electrical parameters: RF power,
temperature, supply voltages and currents and other important information.
•
The D.C. supply is distributed in such a way that, if one of the power supplies fails, the driver
Amplifier and 3 of the output stages are still supplied. In this condition, the surviving supplies will
sustain an output current increase of several Amperes and the amplifier output will drop to
approximately 50% rated power, but service will not be disrupted. In this situation a warning event is
also generated. If two of the power supplies fail, an alarm event is generated. (See also chapter:
Alarm and warning events).
•
Should a transistor of the RF driver stage fail in short circuit, one of the fuses of the D.C. combiner-
splitter circuit will open, and the amplifier output will drop to approximately 25% rated power.
•
The yellow LINE LED, when lit, shows presence of A.C. power mains.
•
The green ON AIR LED is on when the Amplifier is operating under normal conditions. When the RF
power output drops below approximately half power (- 3 dB threshold), this LED is extinguished. This
led blinks if the amplifier is enable and ready.
•
The red ALARM LED is normally dark. It turns on to indicate that one alarm has occurred. In this
condition the Metering, alarm and Protection module immediately disables the amplifier.
•
The red V.S.W.R. ALARM LED is normally dark. It turns on to indicate that the reflected output power
has risen above a pre-set, critical threshold. In this condition the Metering and Protection module
immediately disables the amplifier.
•
The yellow WARNING LED is normally dark. It turns on to indicate that one or more operating
parameters have risen above the normal limiting values. This LED blinks if some past warnings and
alarms are stored in the EEPROM non volatile memory of the microprocessor. This LED turns off only
if the memory has been cleared.
Oct 2013 CMAN0W474G Page 11 11 11 11