T674K 40kW UHF TV Transmitter Description
The ITELCO T674K is a 40 kW television broadcasting transmitter with common amplification of vision and sound carriers,
operating in the UHF band.
This equipment fully complies with safety of personnel rules specified in IEC215.
Each unit is designed to be easily removed and individually checked.
Exciter
The exciter is designed to be used in common amplification transmitters;
it is composed of several plug-ins for easy servicing and simplified updating
in the future.
All routine on-air adjustments are screwdriver adjustable from the front
panel; an etender board is self-contained for servicing.
Driver Amplifier
the driver amplifier is composed of four solid state amplifier units
W612 and a power coupler unit H 613, in order to reach
a driving power of 420W at the input of the final stage.
Each amplifier unit has built -in its proper switch mode power
supply and is self-protected againts overtemperature, overcurrent,
overvoltage, overdrive and high reflected power.
A set of LED shows the status of the unit and a set of test points
make possible the reading of the most important parameters.
Final Amplifier
The final amplifier employs the I.O.T. (Inductive Output Tube)
7360 working in common amplification mode and delivering
around 41kWps. The I.O.T. assembly is mounted on a trolley and can be slided
out in order to facilitate tube replacement : a unique connection
to the output coaxial line has been designed in order to easily disconnect
the I.O.T. assembly.
Power Supplies
The beam power supply is contained in a separate protected enclosure in the
rear side of the driver cabinet and the components are attainable only by
opening a door locked by a latch. Inside the enclosure takes place the HV transformer
(mounted on a trolley in order to facilitate its removal), the HV rectifier, the
smoothing circuit assembly, the HV limiter and the crowbar performing the I.O.T.
protection against internal arcs. The filament power supply unit, the grid power supply unit
and the magnet pwer supply unit are contained in a separate protected enclosure in the rear
side of the final amplifier cabinet, and are attainable only by removing a panel
locked by a latch.
All the efective voltages and currents can be measured and displayed by means
of the graphic display located on the front panel of the G021 transmitter control unit; any
adjustment of the voltage of the different power supplies can be done directly from
this unit.
Transmitter Control System
The transmitter control system is involved in three different operations:
- Control of the start/stop procedure;
- Collection and display of the informations regarding the transmitter;
- Management of the transmitter in case of failure.
The transmitter control system consists of four main sub-systems
linked up according to a master-slave architecture; the G021 is the master that manages
three slave units called Data Acquisition Interface (D.A.I.). Each Data
Acquisition Interface manages several sub-units (e.g. all detectors as cooling
liquid flow and temperature, phases monitor, forward
and reflected power, etc. and all the power supplies, the drier and the exciter):
for each of them it performs the A/D conversion of the electrical magnitudes to monitored,
the D/A conversion of the settings, the data storage and the data communication management.
The data communication between each D.A.I. and the master unit is via optical fiber,
at a bit rates of 40 kbit/s. In order to not loose the memory in case of mains lack, all the transmitter
settings, readings and alarms are stored by a battery backed-u RAM.
Last but not least, all the controls and the signals can be remoted via an optional RS232
interface.
Safety Key Locks
In order to assure safety conditions to the personnel involved in the maintenance and repair
of the transmitter all the units containing components connected to dangerous voltages
are protected and the door can be opened only after opening of the mains breaker
and closing of the earthing switch.
Water Cooling System
The water cooling system is single-circuit type and the circulating liquid is tap water
with antifreeze. This heat is dissipated to the atmosphere through a water-air heat
exchanger.
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