Backplane Assembly; Backplane Dc Interconnect Board; Input Divider Board; Output Combiner Board - Crown FM1000A User Manual

4.1.3 Backplane Assembly

The backplane assembly is located in the vertical center of the PA1000 behind the
power modules. The Backplane Assembly is the common connection point for the
major sections of the transmitter. This assembly consists of the Input Divider
Board, Output Combiner Board, and Backplane Interconnect Board.

4.1.3.1 Backplane DC Interconnect Board

This board is located nearest the metal inner brace of the chassis. It distributes DC
power to each of the four MOSFET amplifiers, provides the interconnections for
control of the power supply, and enables connection to the remote control inter-
face. The Backplane/DC Interconnect Board contains interconnections from the
Control and Metering Board to the DC Fuse and Power Distribution Board, as well
as power connections to the power amplifier modules.

4.1.3.2 Input Divider Board

The Input Divider Board is the middle board sandwiched between the Backplane DC
Interconnect Board and the Output Combiner Board. It provides the power division
and impedance transformation needed to supply proper drive to each of the four
amplifiers (two modules).

4.1.3.3 Output Combiner Board

The Output Combiner Board is located nearest the Output Filter It consists of a
micro-strip transmission line that combines the output power from the four ampli-
fiers (two modules) so that ultimately, all the power comes together at one common
point junction. Here the currents and voltages of all four power amplifiers are in
phase and producing equal RF output power. From this common point junction,
the Output Combiner Board uses a second quarter-wave transformer to convert the
output power to the 50–ohm impedance needed at the output of the unit.
4.1.4 Output Filter & Reflectometer
The Output Filter/Reflectometer is located behind the Backplane Assembly in the
center of the PA1000. See the accompanying schematic in Section 6 for more
information.
The ninth-order, elliptic, low-pass filter attenuates harmonics generated in the
power amplifier. The capacitors for the filter are circuit board pads. The reflecto-
meter uses printed circuit board traces for micro-strip transmission lines. Trans-
mission line segments (with an impedance of about 100 ohms) on either side of a
50–ohm conductor provide sample voltages representative of the square root of
forward and reverse power. DC voltages, representative of forward and reflected
power, go through a bulkhead Filter Board to the Backplane/DC Interconnect
Board, then to the Metering Board where they are processed for power control and
metering and for SWR metering and protection.
Principles of Operation 4–3