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7.
To
enter the relative velocity of the cable under test, press:
i
,;
:......
,.
:.::
:
/
.:>
.<.~~;~~;<.
Lcal]
gg#q
;:~~~~:~~~~~~~~~~~
and enter a velocity factor for your cable under test.
Note
Most cables have a relative velocity of 0.66 (for polyethylene dielectrics) or 0.7
(for teflon dielectrics). If you would like the markers to read actual one-way
distance rather than return trip distance, enter one-half the actual velocity
factor. Then the markers will read the actual round trip distance to the
reflection of interest rather than the “electrical length” that assumes a relative
velocity of 1.
Velocity
Factor
=
-
i,
where
cr
is the relative permittivity of the cable dielectric
8.
lb
position the marker on the reflection of interest, press:
@GiGJ and turn the front panel knob, or enter a value from the front panel keypad.
In this example, the velocity factor was set to one-half the actual value, so the marker reads
the time and distance to the reflection.
9.
To
position a marker at each reflection of interest, as shown in Figure 2-65, press:
..a:.>:
“.~.:.:.:.:.:.:.:.::.::
:‘.::
. . . .
_.“‘....
;-I.;;$
~~~~~~,~
~~~~,~;~,~
t-g
the
front
panel
knob
or
entering
a
value
from
the
L:
//
::.~>>,:.$:.,.:
.,...
,._,,,,
;:.::%>>:..I..
.._........
i
. . .
..Z!
. . . . . . . .
;...:.<m:...
:s .:.:
_...A
w
.A..
~~.~.~~..~.~.~.~.~.~..~
..A..
. . . . . .
..i>
’
front panel keypad after each key press.
J
1
1 1
I
I
CHI STHRT
0
t
STclP
35
n*
aw000026
Figure 2-65. Device Response in the Time Domain
2-80
Making Measurements