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HARRIS
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WARNING: Disconnect and lockout AC primary power prior to servicing
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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 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 module 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 trimming to
compensate for small gain and phase differences between cabinets, to insure the cabinet
outputs maintain the proper phase and amplitude relationships when passed to the 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, vary by
configuration. For details, see the descriptions in the following section on visual the
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:
10 kW HT10HSP and the HT11LSP which is 11kW, Parallel Path,
The AGC output feeds a driver module, whose output passes through a PA module. In
a 10 kW and 11kW transmitters, a 12-way divider feeds 12 PA modules.
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 (also 22kW Low band), the AGC module feeds a phase and gain
module, whose outputs feed two 10 kW (11kW) visual cabinets like those described
above. A 3 dB quadrature hybrid then combines the two cabinet outputs.
