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7.3.2 Vision Driver and Sound PA Cabinet
The low band version uses one vision driver followed by a metering directional coupler.
In the high band version, a four way power divider follows the vision driver output.
Two outputs drive PA modules and two are terminated. The outputs of the two PA
modules are combined with a two-way Gysel combiner. This combined output is
followed by a directional coupler for metering and connected by cable to the drive output
of the cabinet.
The sound RF path will be determined by the required power level. The low band and
high band paths are the same. The power divider is four port, the unused ports terminated.
HT15HS/LS, the path has two PAs after the power divider
HT30HS/LS, the path has four PAs after the power divider
HT45HS/LS, there are two paths combined with an external 3dB hybrid. Each
path has three PA modules.
7.3.3 Combined Sound and Vision 10 KW PA Cabinets
The sound path is the same as the HT15HS/LS: a driver and two PAs. In Low Band
transmitters, the exciter RF output from the AGC or Phase and Gain unit is the input
to a Driver module. The output of the Driver module is divided 12 ways by the Power
Divider. Also in the Low Band transmitters, the PA modules increase the outputs of the
divider by 18.5 dB. In current High Band transmitters, a PA module follows the Driver
module for more gain and drive power. This drive power becomes the input to the Power
Splitter. The outputs are then amplified by the PA modules.
7.4 Power Divider
The power divider uses quarter wave 75 ohm transmission lines to match the output 50
ohm impedance to 112 ohms to make the impedance matching easier. The parallel
combination of the parallel outputs is then impedance matched to be 50 ohms to match
the driver output impedance. See Figure 7-1.
Figure
7-1
Power
Divider