1.2.2 Transmitter Control System 1.2.3 Main Controller

1.2.2 Transmitter Control System 1.2.3 Main Controller
Line voltage samples are provided for the system monitor. All
logic supplies, exciter power and fan in the control cabinet are
controlled by CB-1 (see Figure 1-2). The cabinet may be rewired
to allow the power supplies and exciter(s) to operate on a single
phase Uninterruptible Power Supply. Power Amplifier Cabinet
AC power is fed through CB-1 to the logic supply (see Figure
1-3). AC Contactor K-1 feeds the 50 volt supplies and fan breaker
CB-2 (see Figure 1-4). Auxiliary relay K-2 activates the AC
contactor through commands from the slave controller.
1.2.2 Transmitter Control System
The control system for the transmitter consists of a main controller and a microprocessor monitor mounted in the control cabinet.
Individual slave controllers are mounted in each amplifier cabinet. Each RF module contains a module controller for module
Transmitter ON/OFF, LOCAL/REMOTE, and power
RAISE/LOWER switches are located on the control cabinet, to
the right of the display panel. Monitor Display
The monitor system samples each cabinet and gathers all of the
status and analog data for the display. Data from the system is
interfaced through the monitor board to the display controller,
and shown on the front panel flat display screen as bar graphs
and numerical readings. The display is menu driven, with “soft
keys” below the display panel for accessing and maneuvering
through the various pages of information.
Figure 1-3
Location Of CB1 And CB2 At Front Of PA Cabinet(s)
A HELP key below and to the right of the display panel provides
a short description of the page of information being viewed, to
help non-technical personnel in interpreting the data. Fault Indicators
Fault lamps are located below the display and switches. Each
light, when illuminated, indicates a problem in the following
areas: exciter, VSWR fault, VSWR foldback, power supply,
controller, air, door, fail-safe, phase loss, module, monitor, and
external interlock.
1.2.3 Main Controller
See Figure 1-5 The transmitter main control unit provides a
central point for controlling the entire system on the controller
board. The main controller interfaces with the slave controller(s)
for the amplifier cabinets’ ON/OFF commands, and with the
exciter for power RAISE/LOWER commands.
RF samples are detected for power metering. The main controller
also performs VSWR foldback action by reducing exciter power
The main controller has a battery backup to restore the transmitter to its previous operating condition after a temporary AC
power failure. A power down timer will automatically switch the
transmitter to the OFF state if the power is not restored within
approximately two hours.
Figure 1-4
Location Of K1 At Rear Of PA Cabinets
WARNING: Disconnect primary power prior to servicing.
Figure 1-5
Control System Block Diagram
Remote status and analog outputs and remote control command
inputs are provided by the main controller to a series of D
connectors at the rear of the control cabinet.
1.2.4 Slave Controllers
The slave controllers are mounted in the upper left-hand slot of
each amplifier cabinet. Each is responsible for controlling and
monitoring its PA cabinet.
The slave controllers interface the cabinet to the main controller
and monitor in the control cabinet.
Each slave controller controls a cabinet’s fan motor, 50 volt DC
supplies, and RF amplifier modules. Slave controllers also report
cabinet door interlock status, air interlock status, module faults,
and power supply faults to the main controller.
Cabinet input drive and RF power output samples, collected by
RF peak detectors on the slave controller board, are relayed to
the main controller through the slave controllers. In the event of
loss of the main controller, each slave controller may be used to
operate the amplifier cabinet for emergency service.
1.2.5 Exciter Signal Flow Paths
Refer to the separate exciter manual for data on the exciter. If
optional dual exciters and an exciter switcher are used, both
exciters are supplied modulating signals, and each exciter’s
output feeds the exciter switcher.
1.2.6 Accessory Tray Exciter Switcher (OPTIONAL)
In a dual exciter system, the output of each exciter is monitored,
a fault is generated if the RF output is less than the preset level.
If the exciter driving the transmitter faults, the exciter switcher
can automatically switch to the exciter without a fault. Manual
switching is also available. Phase and Gain Module
In transmitters with multiple PA cabinets, one or more phase and
gain modules divide the power into individual drives for each PA.
Each phase and gain module splits the drive into two parts whose
relative amplitude and phase are adjustable. This allows trimming to compensate for small gain and phase differences between cabinets, so that the cabinet outputs maintain the proper
phase and amplitude relationships for the output combining.
The number of phase and gain modules used depends on the
number of PA cabinets AGC Module
Each PA cabinet has an AGC Automatic Gain Control that
monitors a sample of transmitter drive at the input of the power
divider. The Feedback loop includes temperature compensation
circuitry that reduces the transmitter sample proportional to the
change in temperature. The PA drive will increase as a function
of temperature. When a PA module fails the AGC does not
change drive. This system allows a constant linearity correction
that will prevent problems of out of tolerance operation when a
PA module fails.
WARNING: Disconnect primary power prior to servicing.
1.2.7 RF Amplifier Cabinets 1.25 kW (Average) 5 kW peak
The low band unit has one driver module, a seven way power
divider, seven PA modules and a seven way combiner. The high
band is similar, adding a PA stage between the driver and the
seven way power divider. Two drive samples at the output to the
power divider are used for metering and drive AGC. The cabinet
output line is sampled for cabinet power metering. 2.5 kW (Average) 10 kW peak
Low Band
The PA input RF is amplified by a driver module then divided by
a 14 way splitter. Each splitter output drives a PA module. The
PA’s are combined in a 14 way combiner.
High Band
The driver output is divided by a 4 way splitter, Two outputs are
terminated. The other two outputs are amplified by two PA
modules. The combined output of these two driver PA modules
is divided 14 ways by the drive splitter. Each splitter output is
amplified by a PA module. The PA module outputs are recombined in a 14 way combiner, whose output becomes the cabinet’s
RF output. The higher power transmitters use multiple cabinets
of this basic architecture.
• 5 kW Average Power
In a 5 kW transmitter, the Exciter output passes through a phase
and gain module. The resulting two outputs are followed an AGC
for each of two 2.5 kW PA cabinets. The cabinet outputs are
combined with a 3dB quadrature hybrid combiner.
• 7.5 kW Average Power
In this system, one phase and gain module drives one amplifier
cabinet, and a second phase and gain module. The three outputs
are AGC controlled, one for each PA cabinet.
At the outputs of the three PA cabinets, a 3dB hybrid combines
the first two cabinet outputs, which combine with the third in a
4.77/1.76dB asymmetrical hybrid combiner.
• 10 kW Average Power
The signal from the AGC is divided by one phase and gain unit,
and each signal is divided into two more signals by another phase
and gain unit. These four signals drive four PA cabinets. The
outputs from A and B are combined in a 3 dB hybrid. Similar
outputs from C and D are combined in another 3 dB hybrid. The
outputs from these two hybrids are combined in a third hybrid
1.2.8 RF Amplifier Modules
RF amplifier modules consist of amplifier units called “quarter
modules.” Each quarter module is two push pull amplifiers in
parallel. Only two types of RF amplifier modules are used in the
Platinum Seriestransmitter system. Driver Modules
Driver modules provide high gain (35 dB). Drivers are primarily
used in applications to drive PAs. Digital driver modules are
biased for class A operation. Driver modules are mechanically
keyed so that they cannot be plugged into a PA slot.
Low band drivers contain a single input stage driving a parallel
pair of output stages.
High band drivers contain two series stages and a final stage
consists of two parallel amplifier quarter modules. Driver PAs
Driver PAs are PA modules biased at a higher idle current. They
are not interchangeable with output PAs. In an emergency a PA
module may be re-biased for drive service. Power Amplifiers (PAs)
PAs are used primarily as final amplifiers. Each can supply 1050
watts peak RF output.
PAs are single stage amplifiers, consisting of four paralleled class
AB amplifiers.
1.2.9 50 Volt Power Supplies
The 5 kW Peak transmitter (1.25kW average power) has one
supply. Larger PA cabinets have two 50 volt power supplies.
When two power supplies are used, one supply will be connected
as a delta load, the other as a wye load to reduce supply induced
AC mains harmonics
These regulated supplies convert the AC power to 50 volts DC
for the RF amplifier modules. Each is rated at 300 amps, and
designed to accommodate 10% power line voltage changes.
Internal supply fault protection is interfaced to the slave controller.
1.2.10 Transmitter Output Networks
The transmitter output network has several functions, depending
on the system including combining RF amplifiers, removing
out-of-band signals, and filtering harmonics from the outputs.
WARNING: Disconnect primary power prior to servicing.
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