Harris Platinum Series, Technical Manual

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stages, and a sample of its output is routed to the exciter’s AGC
circuit to hold the exciter’s power output constant.
If optional dual exciters and an exciter switcher are used, both
exciters are fed a video signal, and each exciter’s visual output
feeds the switcher.
1.2.9.2 Transmitter AGC Module
The exciter switcher output or single exciter output then passes
to the transmitter AGC module, whose job is to maintain a
constant gain loop by monitoring a sample of transmitter visual
output, and correspondingly controlling exciter drive.
1.2.9.3 Phase and Gain Module
In transmitters with multiple visual PA cabinets, the AGC mod-
ule passes the RF signal to one or more phase and gain modules.
Each phase and gain module splits the drive into two parts whose
relative amplitude and phase are adjustable. This allows trim-
ming to compensate for small gain and phase differences be-
tween cabinets, so that the cabinet outputs maintain the proper
phase and amplitude relationships when passed to final hybrid
combiner(s).
The number of phase and gain modules used depends on the
number of visual PA cabinets. In transmitters with a single visual
PA cabinet (15 kW and below), no phase and gain modules are
necessary; the output of the AGC module passes directly to the
RF chain.
Since phase and gain modules introduce loss into the system,
additional preamps are sometimes necessary. The locations of
phase and gain modules and preamps varies by configuration;
for details, see the descriptions in the following section on visual
RF chain configurations.
1.2.9.4 Visual RF Amplifier Chains
The Visual RF amplifier chains in the various models vary in
complexity from as few as two amplifier modules to over sixty.
Following are synopses of the various combinations:
•
1 kW (standard)
The AGC output feeds a driver module, whose output is split in
a two-way divider. The two outputs each drive a PA module. The
PA outputs are recombined in a two-way combiner, whose
output becomes the cabinet’s visual output.
•
2 kW (standard)
The AGC output feeds a driver module, whose output passes
through a three-way divider to three PA modules. The PA
outputs are recombined in a three-way combiner, whose output
becomes the cabinet’s visual output.
•
5 kW, 10 kW, and 20 kW (standard)
The AGC output feeds a driver module, whose output passes
through a PA module. In a 5 kW transmitter, this PA’s output passes
through a six-way divider to six more PA modules. In a 10 kW
transmitter, a twelve-way divider and twelve PA modules are used.
The PA outputs are recombined in a six-way (5 kW) or twelve-
way (10 kW) combiner, whose output becomes the cabinet’s
visual output.
In a 20 kW system, the AGC module feeds a phase and gain
module, whose outputs feed two 10 kW visual cabinets like
those described above. A 3 dB quadrature hybrid then combines
the two cabinet outputs.
•
15 kW (standard)
In a 15 kW system, the AGC module’s output feeds a driver
module, which drives a PA module. In a low band transmitter,
the PA’s output is split in a 16-way divider, whose outputs feed
16 PA modules. The outputs are recombined in a 16-way com-
biner, whose output becomes the cabinet’s visual output.
In high band transmitters, the same principle applies, except that
17 PA modules and 17-way dividers and combiners are used.
The 30, 45, and 60 kW transmitter visual chains are multiples
of this basic 15 kW architecture.
•
30 kW (standard)
In a 30 kW transmitter, the AGC output passes through a phase
and gain module. In high band systems, the two outputs are sent
to two preamps. In low band systems, the preamps are not
necessary.
The resulting outputs are sent to two 15 kW visual cabinets (see
15 kW system, above). The cabinet outputs are combined with
a 3 dB quadrature hybrid combiner.
•
45 kW (standard)
In a 45 kW system, one phase and gain module feeds one visual
cabinet and a preamp, whose output feeds a second phase and
gain module. Three outputs are thus obtained. In high band
systems, a preamp is inserted in each path at this point, and the
three outputs pass to the aural PA and visual driver cabinet. In
low band systems, these three preamps are omitted.
The three outputs are each fed to driver modules. In low band
systems, the driver outputs are each passed to one of three PA
modules, whose outputs each drive a 15 kW visual PA cabinet
(see 15 kW system, above).
In high band systems, each of the three drivers supplies input to
a pair of PA modules. The PAs are paralleled into pairs using
two-way power dividers and combiners. The three outputs then
pass to three 15 kW visual cabinets (see 15 kW system, above).
At the outputs of the three visual PA cabinets, a 3 dB hybrid
combines the first two visual cabinet outputs, which combine
with the third in a 4.77/1.76 dB asymmetrical hybrid combiner.
The combined output passes through a harmonic and color notch
filter on its way to the optional diplexer.
•
60 kW (standard)
The AGC module output feeds a phase and gain module, whose
outputs feed two more phase and gain modules.
In low band systems, the four outputs are sent to four driver
modules, which in turn are used to drive four PA modules. These
four outputs drive four 15 kW visual PA cabinets (see 15 kW
system, above).
In high band transmitters, the four phase and gain module
outputs are passed through preamps to four driver modules.
Each driver module output is split using a two-way divider,
whose outputs each drive a PA module. The PA module outputs
1-4 888-2365-001
WARNING: Disconnect primary power prior to servicing.