M/A-Com 19D902797G10, Руководство по обслуживанию

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CIRCUIT ANALYSIS
The microstrip directional coupler samples the output power and produces a voltage, Vf,
proportional to the forward output power. The power control compares the forward
voltage, Vf, to a reference voltage at U3. The output of U3 controls the current flow thru
Q5 and the output of Q203. The collector output of Q203 adjusts the control voltage,
Vct1 and Vct2. This control voltage is capable of adjusting the total PA output power
since it provides the first two stages DC supply to the Low Level Amplifier, U1.
During over-temperature operation, a scaled representation of the forward power is
maintained constant by varying the control voltage line. Thermal resistor RT1, sensing an
increase in temperature, causes the output of U3.1 to increase. If the output of U3.1
becomes larger than the other feedback lines, the output of U3.4 will begin to decrease.
This in turn will cause the output of Q203 to decrease reducing the supply voltage to U1.
Since the scaling is a function of temperature, the power is reduced as the temperature
increases.
Under VSWR cutback operation the reverse voltage, Vr, representative of the reflected
output power, is held below a threshold by reducing the control voltage as necessary. If
Vr increases at U3.2 beyond the preset threshold, an increase at U3.4 will result. This
causes a subsequent reduction in the control voltage to U1. Thus the power control circuit
reduces the output power in order to limit the reflected power to 25% of the set power.
3.2.5 Signal Interface
The signal interface to the MASTR III Power Amplifier is supported by a six position
feedthrough connector, J201, with the following pinout:
1. PWR Sensor
2. PA Key
3. PA PWR Set
4. NC
5. Ground
6. Fil A+
3.2.5.1 Pwr Sensor
This line indicates when the PA is experiencing adverse conditions. Under normal
operation, while the PA is keyed, this line will be proportional to forward power.
Minimum power (zero watts) corresponds to 2.5 volts while maximum power
corresponds to 4.5 volts. This voltage is not temperature compensated and no effort is
made to calibrate this signal to an absolute power level. It is intended to provide a relative
indication of forward power and to discriminate between normal and cutback operation.
Zero volts on this line, when the PA is keyed, indicates the forward power is cutback.
This power cutback may be due to high reflected power or may be due to high PA
temperatures. This fault condition may indicate a problem with the PA or may indicate a
system problem external to the Power Amplifier. High VSWR may be due to a poor
antenna and high temperature may be due to a blocked cabinet vent. Zero volts on this
line, when the PA is keyed, does not indicate zero forward power. Zero volts indicates the
PA is protecting itself due to adverse conditions. If the adverse condition, either high
VSWR or high temperature is eliminated, the power will return to normal and the PWR
SENSOR voltage will rise above 2.5 volts.
8 LBI-38674L