Measuring
Phase
Deviation
Measuring
Phase
Deviation
Deviation
from the
Linear Phase
1.
Specify the
frequency
range
.
2.
Display the
phase trace
by pressing
4
Fo
rmat
5
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N
PHASE
.
3.
A
djust
the
scale
settings
by
pressing
4
Scale
Ref
5
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AUTO
SCALE
.
4.
Press
4
Ma
rk
er
5
.
Then
move
the
marker
to
any of
the points
where the
sloping trace
crosses
the
center
(place
the
marker
on
the
sloping portion
of the
trace,
not the
vertical
phase
\wrap-around").
5.
Press
4
cal
5
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MORE
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ELEC
DELAY
MENU
N
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MKR
!
DELAY
to
add
enough
electrical
length
to
match
the
phase slope
present at
the
marker
frequency
.
6.
Read
the
phase
value
as
a
deviation
from
the
linear
phase
.
By
adding
the
electrical
length
to
atten
the
phase
response
,
the
linear
phase
shift
caused
by
the
DUT
is removed.
The
displayed
response
is
the
deviation
from
the
linear
phase
.
T
o
turn
o
the
electrical
length function,
press
4
cal
5
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MORE
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ELEC
DELAY
MENU
N
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ELECTRICAL DELAY
4
0
54
2
1
5
.
Figure 8-14. Deviation from the Linear Phase
Group Delay
The phase linearity of many devices is specied in terms of group delay or envelope delay
.This
is especially true of telecommunications components and systems
.
Group delay is the dierence in propagation time through
a device as a function of frequency
.
It is measured as a ratio of phase change over
a sample delta frequency as follows:
Gr oup D el ay
=
0
1
3601
F
Where: 1
is phase change [deg]
1F (commonly called the \aperture") is the frequency dierence that gives 1
1. Press
4
Format
5
.
Analyzing the Measurement Results 8-29
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