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2 CIRCUIT DESCRIPTION
The amplifiers are broad band and do not have any tuning adjustments. The "A"
versions are optimized for the frequency range 136-156 MHz while the "B"
versions cover 154-174 MHz.
The dc supply is fed to the amplifiers through resistors R21 and R22. This allows
the collector current of each amplifier to be measured at the test socket.
2.2
Power Splitter/Combiners
The high power versions use zero degree power splitters and combiners. They
consist of lumped element 1/4 wave 70O pi networks and 100O RF resistors (C43-
50, L17-20, R19-20). This configuration provides wider bandwidth and better
balance than lower cost 90 degree hybrids.
2.3
Directional Coupler
The forward and reverse power components are measured throug a coupled line
directional coupler. The output of the coupled line is frequency compensated by
R1-4 and C51-52 before being detected by D1 and D3.
The voltage output of the detectors is proportional to the forward and reflected
power.
2.4
Low Pass Filter
A low pass filter consisting of L12-16 and C39-42 reduces the harmonic
components to less than -80dBc. The filter uses a combination of lumped
elements and printed microstrips to obtain the required harmonic attenuation.
2.5
Power Control Circuits
The forward and reverse voltages from the directional coupler are amplified and
inverted by U2a and U2b. The amplified voltages are combined before
connecting to the input of error amplifier U2d.
Error amplifier U2d compares the detected voltage with the dc reference voltage
from output power trimpot RV2. The amplified difference at the output U2d is
supplied to the rear panel system connector for connection to the T150 ALC input.
2.6
RF Output Indicator
The forward power voltage is compared with the pre-set dc reference voltage from
RV1 and U2c. The output of U2c is used to turn on the RFO LED and provide an
output power logic signal to the test connector.
RF Technology PA150
Page 5
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