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By means
of the SET
TO
FULL SCALE
adjustment, sufficient
gain
is
in
-
serted in the reflected channel to compensate for a
small power loss
in
the transmission
system, and differences between
the
rectification
ef
-
ficiencies of
the two detectors,
up
to
6 db,
are
equalized. Adjusting SET
TO FULL
SCALE on
the
basis
of the
information made
available when a
sliding short
is
used
permits the
Model 416A gain
to
be set at such
point
that the error
signal is not enhanced.
Since the
error signal is proportional
to the
reflection coefficient
of the
load being measured,
whe
n
the
error is
compensated
for at
100%,
it is
compensated
for at other reflection coefficient values
(at the same fre-
quency)
.
7.
Disconnect
the Model X920A
Adjustable
Short,
and
a.
If a slide screw tuner
has been
adjusted
to compensate for the
directivity
error signal, connect to
the slide screw tuner the load
to be
measu
red,
being
careful
not
to
disturb the adjustment of
the
tuner.
b
..
If a slide screw tuner
has not been used, connect the load to be
measured
to the
output
of
the
reflected directional
coupler.
NOTE
:
When operating
in the S
band,
use a Model S920A
Adjustable Short.
Adjustment of Slide
Screw Tuner
When a slide
screw tuner is to
be
used to
compensate for the directivity
error
signal
,
the tuner
m
ay
be adjusted
before or
after
the system is calibrated
.
Full step
-
by -step
procedure
involved
in the calibration
procedures are described
above
.
At
the
time
t
he
tuner
is
to
be adju
ste
d,
the Model
670H
{or HM)
oscillator
has been
set
for
a specific frequency and
its
SELECTOR
switch is at MANUAL.
L
On
the Model 4 16A, set the RANGE
switch
at
-30 DB 3%.
2.
Disconnec
t the
load
from
the output of the
reflected d
ir
ectional
coupler,
and in its
place connect
a
slide
screw
tuner the reflection
from
which
is
adjustable as to
amplitude
and
phase,
such as
Hewlett-
Packard
Model X870A Waveguide
Slide
Screw
Tuner,
and
a movable
low -refle
ction
load, such
as
a Model X914A
Waveguide
Moving
Load
.
This
termination
arrangement
is shown in
Fig
.
13-1.
3
.
On
the Model 670H (or
HM
).
adjust
the ATTENUATION control
while
watching the tuning eye on the Model
416A
.
The ATTENUATION
control
should
be
adjuste
d
to
obtain
an approximately 1/8"
gap in
the
tuning eye shutter.
4
.
There
are now, essentially, three signals
present
in
the system:
( 1)
the
reflection from the
load
,
which is the
desired signal;
(2)
a
signal
which results from imperfect directivity
in the reverse cou-
pler
;
and (3) the reflection from
the
slide
screw tuner
.
-23-
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