Model
8754A
Electrical Length Compensation
Front
Panel
Introduction
Phase calibration requires equal electrical lengths in the reference and test signal paths. The electrical
length
is
equal when the phase angle
is
constant over the frequency sweep with the standard connected.
For
fine adjustment
of
electrical length
two
independent controls, PHASE
B/R
LENGTH for
the
trans-
mitted signal
path
and POLAR
A/R
LENGTH for the reflected signal path, provide up
to
16 centimeters
of
intemalline
length equalization adjustment. Beyond this limit the reference and test signal
path
cables
must be selected
to
obtain equal electrical lengths.
Reference
Reference
-90
Constant phase response
is
identified
by
a flat trace for a rectangular display
or
a small cluster for a polar
display.
If
the
phase angle becomes more negative with increasing frequency, then
the
test signal
path
is
longer
than
the
reference signal path. Therefore, length
must
be added
to
the
R-input signal
path
if
the
range
of
the front-panel LENGTH controls
is
insufficient.
If
the
phase angle becomes more positive with
increased frequency
then
length must be added
to
the
A
or
B
input
signal path.
When making reflection
or
transmission measurements using
the
8502
or
8748
test set,
the
usual test setup
uses R
input
as
the
incident signal, A
input
as
the
reflected signal, and B
input
as
the
transmitted signal.
With this setup, first adjust
the
A and R lengths
to
equalize
the
POLAR
A/R
display when calibrating
reflection coefficient (open
or
short). Then adjust
the
B length
to
equalize
the
PHASE
B/R
display when
calibrating transmission (through).
15
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