POWER
AMPLIFIER
1.5KW
HIGH
BAND
40D1493G3
PUB96
‐
29
Rev
2
August
2007
29-4
PA
Module
Adjustment
of
bias
voltage
to
establish
proper
quiescent
FET
bias
current
Important:
50
Ω
input
and
output
terminations
are
necessary
to
achieve
consistent
results
and
prevent
damage
to
the
devices
when
testing
modules.
Supplemental
cooling
is
not
required
when
performing
bias
adjustments
or
low
power
sweep
of
the
PA
modules.
•
Remove
all
fuses
from
the
module
to
be
tested.
(There
are
12
fuses
in
total).
•
Adjust
all
bias
pots
to
maximum
resistance,
for
minimum
bias
voltage.
(Again,
there
are
12).
•
Use
a
clip
lead
to
short
the
junction
of
C5,
R6,
and
R7
to
ground.
This
shuts
off
side
B
of
the
amplifier
so
it
will
not
interfere
(through
L9)
with
measurement
of
quiescent
current
from
side
A.
•
Terminate
the
RF
input
and
output
into
a
50
Ω
load.
•
Apply
+50VDC
from
the
front
panel
test
point
on
the
transmitter,
through
an
ammeter,
to
the
positive
copper
bus
bar,
and
its
negative
to
chassis.
Caution:
Observe
polarity!
•
Check
the
voltage
on
the
bias
terminals,
it
should
be
39
V
±2
V.
(The
bias
terminals
are
connected
together
via
insulated
bus
wire).
•
Read
the
current
drawn
by
the
VSWR
board
and
bias
regulator.
Next,
install
a
fuse
in
side
A
(nearest
the
panel)
of
amplifier
#1;
adjust
the
corresponding
bias
pot
for
a
500
mA
increase
in
the
power
supply
current;
this
increase
corresponds
to
an
idling
bias
current
of
0.5
A
(750mA
for
digital
operation).
Remove
the
fuse.
Remove
the
side
B
bias
short
and
place
it
on
side
A
at
the
junction
of
C6,
R2,
R3
and
R9.
Place
the
fuse
in
side
B.
Adjust
the
side
B
bias
pot
for
the
proper
current.
•
Move
the
fuse
to
the
remaining
fuse
holders,
one
at
a
time,
and
adjust
each
companion
bias
potentiometer
in
the
same
manner
for
the
proper
bias
current.
•
Install
remaining
fuses
and
remove
the
bias
short
after
all
bias
adjustments
have
been
made.
Low
power
sweep
of
amplifiers
Note:
Low
power
sweep
of
PA
modules
should
not
be
required
under
normal
circumstances
–
even
when
replacing
FET
devices.
There
are
no
tuning
adjustments
on
these
modules.
•
Ensure
that
terminations
are
in
place
in
the
test
setup.
All
modules
require
50
Ω
source
and
load
impedances
to
prevent
damage
and
for
consistent
results
during
testing.
•
Connect
the
module
to
a
sweep
system,
typically
as
shown
in
Figure
1.
The
sweep
generator
should
be
adjusted
to
give
a
linear
sweep
from
160
to
240
MHz
so
that
all
of
High
Band
or
Band
III
is
swept,
with
a
small
amount
of
out
‐
of
‐
band
signal
on
both
ends.
•
Connect
the
lab
power
supply
+50
V
to
the
positive
supply
bus
bar,
and
the
negative
to
the
chassis
of
the
amplifier.
The
current
should
be
limited
to
7
or
8
A
for
this
test.
Caution:
observe
polarity!
•
With
the
power
supply
switched
on,
the
current
drawn
should
be
not
more
than
the
bias
current
for
all
the
devices
together
‐
about
6
amperes
(12
x
0.5
A)
for
the
PA
module.
•
The
swept
in
‐
band
frequency
response,
for
High
Band
modules,
should
be
essentially
flat
within
±1
dB
as
shown
in
Figure
1,
with
gain
approximately
15
to
16dB.
