Potomac Instruments FIM-21 - Page 17

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SECTION
2.
OPERATION
(Cont.)
2.6
R.
F.
Brid
ge Measurements (Tuned
Voltmeter)
(Cont.)
Connect
RF
source
to
EXT
RF
input
on
FIM
front
panel.
Adjust
RCVR
tuning
for
desired
frequency
and
highest
reading:
adjust
FUIJ,
SCALE
switch
for
an
on-
scale
reading.
To
calibrate
the
FIM
for
absolute
voltage
me
asure
m
ent
s;
set
RCVR
tuning
to
desired
frequency
with
signal
source
connected
to
EXT
RF
input
switch
settings
as
in
steps
1,
3
&
4
above.
The
LOG-LlN
switch
nrust
be
set
to
the
LThl
position
fo
r
absolute
readings.
Switch
the
RF
ThTPUT
switch
to
ANY
and
calibrate
me
ter
as
described
in
Section
2.3.
Return
RF
ThTPUT
switch
to
EXT
and
read
meter.
The
correct
voltage
is
obtained
by
correlating
the
m
eter
indication
and
the
FULL
SCALE
attenuator
setting
as
previously
described
.
IMPORTANT
NOTE
When
operating
the
FIM
as
a
tuned
voltmeter,
it
is
necessary
to
g
uard
against
severe
overload
at
the
EXT
RF
input.
For
thi
s
reason,
start
all
measurements
in
the
lOV
FULL
SCALE
switch
position.
The
maximum
input
level
which
can
be
applied
to
EXT
input
without
causing
damage
is
25
volts
RMS
.
2-7