HP 8753D - Page 397

Figure
6-71.
The
Eects
of
Windowing
on
the
Time
Domain
Responses
of
a
Short
Circuit
Range
In
the
time
domain,
range
is
dened
as
the
length
in
time
that
a
measurement
can
be
made
without
encountering
a
repetition
of
the
response
,
called
aliasing.
A
time
domain
response
repeats
at
regular
intervals
because
the
frequency
domain
data
is
taken
at
discrete
frequency
points
,
rather
than
continuously
over
the
frequency
band.
M
easur
ement
r
ang
e
=
1
1
F
where
1F
is
the
spacing
between
frequency
data
points
M
easur
ement
r
ang
e
=
( number
of
points
0
1)
f
r
eq
uency
span
(
H
z
)
example:
M easur
ement
=
201
points
1
M
H
z
to
2
:
001
GH
z
Rang
e =
1
1
F
or
(
number of
points 0
1)
f
r
eq
uency span
=
1
(10 2 10
6
)
or
(201 0 1)
(2 2 10
9
)
= 100
2 10
0 9
seconds
E lectr ical leng th
= range
2 the speed
of lig ht
(3 2 10
8
m=s )
= (100
2 10
0 9
s ) 2 (3 2 10
8
m=s )
=30 meters
In this example, the range is 100 ns, or 30 meters electrical length. To prevent the time domain
responses from overlapping, the test device must be 30 meters or less in electrical length for a
transmission measurement (15 meters for a reection measurement). The analyzer limits the
stop time to prevent the display of aliased responses.
6-130 Application and Operation Concepts