AR 1000T2G8B, Руководство по эксплуатации и обслуживанию

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Rev - 5
2. THEORY OF OPERATION
2.1 DESIGN OF THE AMPLIFIER
The Model 1000T2G8B TWT amplifier consists of four principal subsystems. From top to bottom, these are
the control module (A28010-303), the RF combiner assembly (A28005-004), and the two TWT power
supplies (A28012-000). These will be discussed in greater detail below. The system is completed by a number
of cables that interconnect the subsystems, and by the rack assembly.
See the build tree in section 5.1 for information about how the parts lists are structured.
2.2 CONTROL MODULE
The control module houses the microprocessor control system (control head), the data steering assembly, a
three-output DC power supply, a 28 VDC power supply, and an AC contactor for removing the AC power
from the TWT power supplies when the control module’s AC power switch is turned off.
The control head consists of three boards: the display board (A25425-000) provides the user interface
(display, buttons, and rotary encoder); the CPU board (A25450-000) contains the CPU, bus management
hardware, DRAM, EPROMs, and static RAM; and the the datalink board (A22488-003) provides the I/O to
the amplifier system as well as the IEEE-488 communication bus for computer interfacing.
The control head is provided with its own power supply and, other than thru the interface bus, is electrically
isolated from the amplifier. Communication with the amplifier is via fiberoptic links. The single pair of links
on the control head fans out to three pairs of links in the data steering assembly (A21175-000). These links go
to interface boards in the RF combiner and in each of the two power supplies. The data is “steered” by an
address byte in the data stream from the microprocessor. To make the connections between various chassis
backpanels, the fiberoptic data is converted to twisted/shielded pairs by line driver/receiver pairs on the three
F/O to RS-485 adapter boards (A28008-000). In the RF combiner and in the power supplies, the signals are
converted back into fibers by means of the same boards.
2.3 DESCRIPTION OF THE RF COMBINER ASSEMBLY
The TWTA consists of two stages of RF amplification: a high-gain, 4 watt solid state driver amplifier
(E01611-000), and a power-combined pair of traveling-wave tube amplifiers (E01608-000).
The type N RF input connector is located on the rear panel. The RF input is fed to the input connector on the
solid state preamp with a built-in voltage-controlled variable attenuator which permits control of the
amplifier’s output power from the control module. The amp’s output is split by a 180° hybrid. Each of the
hybrid’s secondaries is connected to the RF input of a TWT. The TWTs’ outputs are connected by waveguide
to the input ports of a magic tee (waveguide 180° hybrid) (E01607-000). The magic tee’s sum port, the port
that collects all in-phase products, is terminated with a 500 watt waveguide load. The magic tee’s difference
port, the port that collects the out-of-phase products, is connected to the RF output.
The electrical length of the circuits between the splitter and the combiner must be matched (so that the 180°
out-of-phase relationship will prevail across the full bandwidth, permitting efficient combining). To achieve
this, phase-matched cable assemblies and adjustable line stretchers are used.
Since the fundamental frequencies are amplified 180° out of phase, the second harmonic products, which
represent significant power in the lower part of the band, are largely in phase, and are dumped in the sum