AR 10036484, Руководство по эксплуатации и обслуживанию, Страница: 46 / 58

Model 3000W1000B
30 Rev A
3.2.3 A2, A4-A6 Driver Amplifiers (Schematic 10036697)
The A2, A4-A6 Driver amplifiers consist of RF matching circuits, RF transistors, DC current control circuits,
DC switching circuits and fault detection circuits.
The RF input is fed to a 4:1 transformer composed of T1, T2, and T3. The push-pull output signal of the 4:1
transformer is connected to the gates of push-pull connected Q1. The drains of Q1 are connected to a 4:1
transformer composed of T4, T4 and T6. The RF transistor , Q1, has approximately 22.5 VDC applied to the
drains at 4 amps current for the driver and 7 amps current for the finals. The RF stage has approximately 18
dB of gain for the finals and an output compression point of 50 watts or greater.
Voltage comparator U1 senses the presence of the –8 VDC. The output of U1 is high if the –8V supply is
–5.5 or less. The output of U1 pulls low when the –8 volts is present turning on Mosfet Q2 which supplies
the DC voltages to the drain of Q1.
The current through Q1 is monitored by U2. The output of U2 is fed to an op amp (U5) which has a
reference voltage on the non-inverting input and it compares the output of U2 to the reference voltage and
generates an error signal to vary the gate voltage of the RF transistor Q1 which controls the drain current.
U3 is a positive 5V regulator. It supplies DC to the current sense circuit, U2, the op amp, U5, and the fault
detection circuit, U6. SW1 is a thermal switch. It closes at a heat sink temperature of approximately 70
˚
to
protect the module in the event of an over-temperature condition.
3.2.4 A8-A10 Two-Way Splitter
The Two-Way splitter splits the input signal into two equal-amplitude, equal-phase signals. The amplitude of
each signal is 3–3.5 dB below the input signa
l when both outputs are terminated into 50Ω loads.
3.2.5 A14 Dual Detector Assembly (Schematic 10033688)
The Dual Detector monitors the outputs from the A14 dual directional coupler. The dual detector provides
sample outputs of the forward and reverse powers and also DC outputs proportional to the forward and
reverse powers of the amplifier.
There are two identical channels in the dual detector; only the one J1 input is described. The input from J1 is
connected to a two-way splitter. The two-way splitter outputs go to a 6 dB attenuator (U3) and the RF input
of the power detector (U2). The power detector provides a DC output which provides a signal to display
output power and for amplifier protection. The output of attenuator (U3) is fed to a stage of gain (U4) which
is connected to a 3 dB attenuator (U5). The output from U5 provides an RF sample output which can be used
to monitor the amplifier output power. The gain from J1 to J2 is approximately 1.0 to 1.5 dB of gain.