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MSF
5000
Instruction Manual
Chapter
1
Description
Power Amplifier
Power Amplifier
68P81092E02
3/19/94
The Power Amplifier (PA) is mounted in
the front
portion of
the cabinet
directly
in
front of the Power Supply.
Two models of PAs
are described:
low
and
high
power.
For high power
models, two separate
PAs
and Power Supplies
are
required. One
PA
is the
driver PA
and the other is
the
final PA. The driver
PA
is
mounted directly below the final PA.
The driver
PA
receives an intermediate
level modulated
RF
signal from
the
IPA. It
amplifies the signal for transmission
via
the site
transmit antenna. Refer to Figure
1-38.
Forward
and reflected voltages
are detected
by
the directional
coupler and
routed to the power control circuitry on the Uniboard.
PA
temperature is detected
by
a
heatsink temperature
thermistor.
The
temperature is converted into
a
voltage
and routed to
the
power control circuitry on
the
Uniboard.
The final PA
receives
a
modulated
RF
signal from
the
driver PA. Refer
to
Figure
1-38.
The signal is split up
to
six ways, amplified, and combined. The output is fed
to a
directional coupler. Outputs from
the
directional coupler
are the same as
those for the
driver PA. The design of
the
final PAs allows
the transmitter to
continue
to
safely operate at
a
reduced power output
if
one
of
the
final amplifier
stages fail.
Both the
driver and final PAs
feature metering
jacks for measurement of amplifier
module current
to
facilitate servicing of
the
PA.
Several types and power ratings of PAs
are
available for
the different frequency
bands.
The following lists
the
various types of PAs:
OO
6
Watt,
VHE,
UHF
-
No PA is
used
in
this configuration. The
RF
output path
is directly from the
IPA
module
to the site
antenna,
via
the
directional
coupler and
a
low-pass
filter.
15
Watts,
UHF
25
Watts,
VHF
-
may
be used as a
final amplifier for
the 25
watt
configuration or
as a
driver amplifier in
the 350
watt configuration
35
Watts,
800
MHz
40 Watts,
UHF
75
Watts,
VHE, UHF,
800
MHz,
900
MHz
110
Watts,
UHF
125
Watts,
VHF
150
Watts,
800
MHz,
900
MHz
225
Watts,
UHF
.
350
Watts,
VHF
a
The
PA
can be tilted
outward
after
removing
the screws securing
it
to the cabinet
frame.
All
PA
connections are made at the
right
or left end of the
PA
heat
sink,
beneath
a
cover plate.
1-69
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