Agilent Technologies N1996A-503 User Reference page 232

Mode
Distance To Fault
NOTE
Although you can set your number of points to 256, 512, or 1024, you
will only ever be able to save 256 data points when you save trace data.
This is because only 256 points are ever used to display the trace,
regardless of how many points you have used to actually make the
measurement. You will not, however, be losing any resolution, or
reducing the quality of your data. The results will still reflect the true
number of data points that you specified.
Automatic and Manual Distance to Fault Measurements The spectrum analyzer provides
two ways of measuring distance to fault:
Automatic Frequency Range. You select the measurement distance and the spectrum
analyzer automatically selects the Start Frequency and the Stop Frequency. This
measurement distance is set using the
FREQ Channel)
(accessed by pressing
are the same. There are 256 measurement points across the distance you set. This
approach provides the maximum measurement resolution across the selected distance.
The disadvantage is that the start and stop frequencies are automatically set and may
limit the spectrum analyzer's ability to sweep through filters or lightning protectors. This
mode is best used for checking a cable that has no frequency limiting devices.
Example 1: If you set
and you specify 256 Data Points, the instrument automatically selects a
Stop Freq
10 MHz and a
Example 2: If you again set
(197 ft.), but this time you specify 1024 Data Points to give you greater resolution, the
instrument automatically selects a
Manual Frequency Range. When set to Manual, you must specify the Start Frequency and
the Stop Frequency, and the measured distance is worked out from these frequencies.
Generally, the typical start and stop frequencies you use will result in a measured distance
that will be larger than the distance over which you want to look for faults.
The Measured Distance and the Displayed Distance can be different. The distance over
which the instrument has made its measurements, and which has been derived from the
frequencies you specified, is called the Measured Distance. This is displayed at the top
right corner of the measurement screen.
The Displayed Distance refers to that part of the entire Measured Distance that you
choose to display on your measurement screen. You set the Displayed Distance manually
Start Distance
by pressing the
menu.
To help isolate faults over the length of interest, you can set a displayed distance less than
the measured distance. The displayed distance is set using the
Distance
menu keys on the
Keep in mind that there are 256, 512, or 1024 measurement points across the measured
distance. The exact number of measurement points is set using the
the measurement points across the chosen displayed distance will be a ratio of displayed
232
Distance
. In this mode, the displayed and measured differences
Start Distance
to 0 m (0 ft.). and the
of 303.228 MHz.
Start Distance
to 0 m (0 ft.). and the
Start Freq
Stop Distance
and the
Freq/Dist/Calibrate
menu.
Freq/Dist/Calibrate
menu key on the
Stop Distance
Stop Distance
Stop Freq
of 10 MHz and a
Freq/Dist/Calibrate
menu keys on the
Start Distance
FFT Size
menu
to 60 m (197 ft.),
Start Freq
of
to 60 m
of 1.183 GHz.
Stop
and the
key. Therefore,
Chapter 3