Harris Platinum Series, Technical Manual

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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, mod-
ule faults, and power supply faults to the main controller.
Cabinet input drive and RF power output samples, collected
by RF peak detectors, are relayed to the main controller
through the slave controllers as well.
In the event of loss of the main controller, each slave may be
used to operate its amplifier cabinet for emergency service.
1.2.7
50 Volt Power Supplies
Each PA cabinet has one or two 50 volt supplies, depending
on system configuration. These supplies convert the AC power
to 50 volts DC for the RF amplifier modules. Each is rated at
300 amps, and regulated to hold the transmitter power stable
despite power line voltage changes. Internal fault protection is
interfaced to the slave controller.
1.2.8
RF Amplifier Modules
Only two types of RF amplifier modules are used in the aural
and visual chains of any given Platinum transmitter system:
1.2.8.1 Power Amplifiers (PAs)
PAs are used primarily as final amplifiers. Each is capable of
supplying 1050 watts RF output, either aural CW or visual peak
sync. PAs are also used as interstage amplifiers in larger visual
cabinets, to drive several subsequent parallel PA modules.
PAs are single-stage amplifiers, consisting of paralleled class
AB amplifiers, in both high and low band transmitters.
1.2.8.2 Driver Modules
Driver modules provide high gain. Primarily used in preamp
applications to drive PAs, they are also used as aural final
amplifiers in low power applications. Driver modules are
keyed so that they cannot be plugged into a PA slot.
Low band drivers contain two cascaded class A stages. High
band drivers contain two class A stages and one class AB stage.
In both cases, the final stage in a driver consists of two
paralleled amplifier blocks.
1.2.9
Visual Signal Flow Path
A basic visual signal flow topology is common to all Platinum
Series

transmitters. For the following discussion, refer to the
transmitter block diagram in the drawing package.
1.2.9.1
Exciter
Video is applied to the exciter where it is clamped, pre-cor-
rected for differential gain and differential phase, and modu-
lated onto the IF carrier (37 MHz for system M/NTSC, 38.9
MHz for B/PAL). Next, frequency response and group delay
are corrected. Vestigial sideband filtering follows. The IF
signal then passes through an AGC amplifier to correctors for
linearity and ICPM.
A local oscillator and mixer in the exciter upconvert the IF
signal to the transmit frequency, and the resulting signal is
bandpass filtered and amplified. The exciter’s final amplifier
is capable of supplying up to 1 watt peak sync to subsequent
Figure 1-5. Control System Block Diagram
Section I - Introduction
888-2365-001 1-3
WARNING: Disconnect primary power prior to servicing.