Axcera 5720 Series, Руководство пользователя

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Bias Protection Board
The RF power transistors contained in the amplifier module are supplied current and voltage
through the bias protection board. The number of transistors contained in the amplifier
module determines the size of the Bias Protection Boards as listed in the previous table.
Logic circuitry on this board protects the transistors by shutting off power to the module in
the event that the gate bias voltage is lost. This circuitry also monitors the status of the
amplifier module and triggers fault conditions in the Control and Monitoring Module if either
a transistor is damaged or the gate bias voltage is lost.
Dual Power Detector
Detection of the forward and reflected output power levels is performed by the Dual Power
Detector Board. This board produces DC outputs representing the forward and reflected
output power levels of the transmitter. Depending on the type of modulation used in the
system the Power Detector can be configured for either average power detection or peak
power detection by positioning the selection jumper on the back of the board. If the system
is to be used to transmit a QAM signal average detection should be selected. If the system is
to be used to transmit an analog video signal the peak detection should be selected. There
are also a set of potentiometers and test points on the front of the module to provide a
means of calibrating the detection circuitry. There are two zero adjustments and
two metering level adjustments used to calibrate the detector outputs for 1V at 100% power.
When the transmitter is used with an analog video scrambling system that suppresses the
synchronizing pulse there are two additional potentiometers provided to realign the power
detection with these types of video signals. They work with a gating pulse that is applied to
the detector module and is provided by the scramling system. This pulse signals the detec
tor to readjust its gain during the regions of video where the synchronizing pulse has been
suppressed.
Power Amplifier Module Controls
Potentiometers Description
FWD LEV Forward Level Adjust potentiometer calibrates the forward power metering level.
REFL LEV Reflected Level Adjust potentiometer calibrates the reflected power metering level.
FWD ZERO Forward Zero Adjust potentiometer calibrates the zero level for the forward power
metering.
REFL ZERO Reflected Zero Adjust potentiometer calibrates the zero level for the reflected power
metering.
GATE LEV Gate Level Adjust potentiometer sets the detected forward power level in conjunction
with an external gating pulse provided by certain video scrambling systems to properly
reference the peak power level.
GATE TMG Gate Timing Adjust potentiometer sets the trigger timing of an external gating pulse
provided by certain video scrambling systems to properly reference the peak power
level.
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