Continental Electronics 816R - RF Circuits Overview; IPA Amplifier Module

Figure 2, 816R Functional Block Diagram
1. RF CIRCUITS
Refer to Figures 2 and 4 for a simplified
diagram of the RF drive path. The drive path
consists of the exciter A4, intermediate
power amplifier (IPA) A3AR1 with its
directional coupler A3DC1, coupling
capacitor A12C1, and power amplifier (PA)
VI with its grid tuning components A12C3,
A12L1-L3, and A12C2.
IPA Amplifier Module, A3AR1
The IPA is a modular amplifier mounted in a
roll-out drawer. The amplifier is a broadband
solid state (MOSFET) design, rated to 700
Watts with internal protection if the VSWR,
supply voltage, RF output power, or heat
sink temperature exceed preset limits. The
protection circuit will turn the module off and
render a "fault'' indication until the above
parameters return to normal.
The IPA receives its de power from a 45 V
de supply on A5. The IPA is followed by a
directional coupler, A3DC1. The coupler
drives the IPA RF power meter. The RF
output of the directional coupler is connected
to the RF power amplifier cavity.
IPA Metering, A3.
The IPA metering panel permits measurement
of IPA supply voltage, current, forward RF
power, and reflected RF power. Additionally,
the panel has three LEDs which indicate
power on, high VSWR, and IPA
module fault. The module fault lamp lights
when the module ’ s internal protection
circuitry shuts the module off. The metering
panel printed circuit board contains all meter
calibration pots, a voltage regulator (Ul), an
op amp/comparator (U2), and the metered
parameter select switch (SI). The op amp
amplifies the reflected power signal (U2-5)
from the IPA directional coupler. This signal
is compared to a reference voltage using the
comparator of U2. When the reflected power
signal (U2-3) exceeds the reference voltage
(U2-2), U2-1 goes high, causing the VSWR
LED to light. The metering circuitry is
powered from the 45 V de IPA supply
through R1 and Ul on the card. Device Ul is
a 12 V de regulator.
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