8.
Press
4
SCALE
REF
5
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ELECTRICAL
DELAY
and
turn the
front panel
knob to
increase
the
electrical
length
until
you
achieve
the
best
at line
,as
shown in
Figure 2-30
.
The
measurement
value
that
the
analyzer
displays
represents
the
electrical length
of your
device
relative
to
the
speed
of light
in free
space.
The physical
length of
your device
is
related
to
this
value
by
the propagation
velocity of
its medium.
Note
V
elocity factor
is
the
ratio
of
the
velocity
of
wave
propagation
in
a
coaxial
cable
to the
velocity
of
wave
propagation
in
free
space
.
Most
cables
have
a
relative
velocity
of
about
0.66
the
speed
in
free
space
.
This
velocity
depends
on
the
relative
permittivity
of
the
cable
dielectric
(
r
)
as
Vel
ocityF
actor
=
1
p
"
r
where
r
is the
relative permittivity
of the
cable
dielectric
You
could change
the velocity
factor
to
compensate
for
propagation
velocity
by
pressing
4
CAL
5
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VELOCITY
FACTOR
(enter
the value)
4
x1
5
.This
will help
the
analyzer
to
accurately
calculate
the
equivalent
distance
that
corresponds
to
the
entered
electrical
delay
.
Figure
2-30.
Example
Best
Flat
Line
with
A
dded
Electrical
Delay
9.
T
o
display
the
electrical
length,
press:
4
SCALE
REF
5
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ELECTRICAL
DELAY
In this example
, there is a large amount of electrical delay due to the long electrical length
of the SA
W lter under test.
Measuring Phase Distortion
This portion of the example shows you how to measure the linearity of the phase shift over
a range of frequencies
. The analyzer allows you to measure this linearity and read it in two
dierent ways: deviation from linear phase
, or group delay
.
Deviation From Linear Phase
By adding electrical length to \atten out" the phase response, you have removed the linear
phase shift through your device. The deviation from linear phase shift through your device is
all that remains.
2-32 Making Measurements
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