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HARRIS
888-9058-001
WARNING: Disconnect and lockout AC primary power prior to servicing
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The high band driver module consists of two cascaded class A stages, driving a third
stage consisting of two parallel class AB amplifier blocks.
A pi input attenuator (R4/R5/R6 on the input Driver RF interconnection assembly) is
used to set the overall gain of each high band driver to 35 dB. The input attenuator also
serves to improve the modules input return loss.
The attenuator feeds the first amplifier stage, which produces about 17 dB gain. Its
output passes to a 2 dB fixed attenuator, used to improve the output match seen by the
first stage. The signal then passes through a L-section matching network to the second
class A stage.
The RF signal then feeds the 2-way Divider assembly. On this divider assembly there is
in the signal path a microstrip directional coupler (which provides a forward drive power
sample for overdrive protection), a microstrip trombone line section (for phase
adjustment), and a Wilkinson 2-way microstrip divider. The dividers two outputs drive
two parallel Class A amplifiers. The outputs are recombined using a Wilkinson
microstrip combiner, which passes the signal through a directional coupler to the
module output. The directional coupler provides a reflected power sample to the modules
protection, control and monitor (PCM) system.
On the input and output Driver RF Interconnection assemblies are provisions for
response correction. On the A5A6 assembly are C4 and C12. On the A5A4 RF
interconnection assembly is C13. On the two way divider RF Interconnection assembly
is C14. These capacitors are added as needed for response correction.
High band drivers have a rated output of 65 Watts average.
8.2.3 PA Module
(Refer to the RF PA Module Schematic, Tab 1000 in drawing package)
PA modules consist of four parallel class AB amplifier blocks. Low Band PA modules
produce 18.5 dB gain overall, and the gain for a high band PA is 13.7 dB. Quarter
module bias can vary depending on application and transistor parameters.
Analog/Digital PA quarter modules were biased at 300 or 400 mA. per FET dependant
on the channel and the FET parameters. Special PA modules used in the drive chain of
classic digital transmitters will be biased at 0.8Amps for low band and 0.7 Amps for high
band per RF FET.
The module RF input signal feeds the 2-way Divider assembly. On this divider
assembly there is in the signal path a microstrip directional coupler (which provides a
forward drive power sample for overdrive protection), a microstrip trombone line
section (for phase adjustment), and a Wilkinson 2-way microstrip divider.
