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NOTE
:
If
greater
accuracy
is desired
,
at
this time follow the procedure
described
under
Adjustment
of Slide Screw Tuner
,
below,
6.
On
the Model 416A
:
b
.
In
single
-
frequency operation
,
with
a short across the
line
,
SET TO
FULL
SCALE may
be
adjusted to obtain a meter indication
of
exactly
100%.
Calibration
at
Single Frequency
with
Slidi
ng
Short
By using a
sliding short which varies the phase
of
the
100%
reflection
during
calibration
,
it is possible to
detect the magnitude of
an error signal
which
is
proportional to the
reflected voltage.
By
calibrating while
using a
sliding
short, the
possibility of
doubling
the
error
is
avoided
0
(Since the error
being
compensated
for
is in
proportion
to the
reflecte
d
voltage
. i
f a fixed short
happened to be so
placed that
the
phase
of the reflected voltage was 180° out
of phase
with
that of
the
incident voltage while SET TO
FULL SCALE
is
being
adjusted,
the error
could be doubled
o
)
When a reflectometer
system is calibrated while
using a sliding short,
and
the directivity
error signal also
is
canceled (by
use of a
slide
screw
tuner
and
moving load)
,
the reflectome
ter
system
will
be adjusted
for measurements of
maximum
accuracy
.
At
the frequency at
which
the
system
is calibrated
,
meas
-
urements will be accura
t
e within
±0
005
for reflection
c
oefficients below 0
,
3.
To
calibrate with a
sliding
short
,
such
as
a Hewlett
-
Packard Model X902A
Adjustable
Short,
proceed
as
follows
:
1.
On the
Model 670H (or
HM)
a.
Se
t
the FREQUENCY
-
KMC d
ial
for the
desired frequency
.
b
.
Set the SELECTOR switch at the MANUAL
position
.
c.
Adjust the ATTENUATION control
whi
le
watching
the tuning eye
on
the
Model 416A.
The ATTENUATION control should
be ad
-
justed to obtain an approximately 1/8
11
gap
in
the tuning eye
shutter
.
NOTE
:
For
maximum
accuracy, at
th
i
s time
follow
the
procedure de
-
scribed
under
Adjustment of Slide
Screw Tuner, below.
2.
Disconnect
the load
,
and
in
its place connect a
sliding
short such as
a
Model
X920A Adjustable
Sho
rt.
NOTE
:
If
a slide
screw
tuner has been adjusted to cancel the
directivity
error,
connect
the sliding short to the
slide
screw
tuner, as
in
-
dic
ated
in Fig
.
12
-
1.
DO NOT DISTURB
the
adjustment
of the
slide screw
tuner.
-
21
-
......
0
'-.....
N
O'
'-.....
Ul
Ul
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