BIRD SITE ANALYZER SA-1700EX, Operating Instructions Manual

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Bird Site Analyzer
54
span; the Site Analyzer calculates the frequency span
for you. If you manually enter a maximum distance, be
sure to select the data points
before entering the max
distance
Note:
If you select a maximum distance that is
less than the total length of the cable system, the trace
might show a spike that is not really a fault, but
rather an echo from the remaining portion of the cable
that is beyond the length you chose. Such a spike is
known as an alias. To avoid aliasing, you should
always set the maximum distance to a value that is a
few feet or meters greater than the entire length of
your cable system.
Data Points If you increase the number of data
points you will increase the measurable distance (475
points results in twice the distance of 238 points, and
949 points results in four times the distance of 238
points) (refer to Equations, page 152). When you
change the number of data points measured, the soft-
ware automatically recomputes the new maximum
measurable distance. If you manually enter a maxi-
mum distance, be sure to select the data points
before
entering the max distance. Changing data points does
not turn calibration off.
Frequency Span If you narrow the frequency span
you will increase the measurable distance (refer to the
Fault Location Distance Tables, page 152).
Velocity of Propagation The velocity of propaga-
tion is a characteristic of the cable and is expressed as
a percentage. Contact the cable manufacturer to get
the velocity of propagation value for the cable you are
using.
Setting the Frequency Span
For a given number of data points (238, 475, 949),
entering a frequency span causes the Site Analyzer to
calculate and enter the maximum measurable dis-
tance and, conversely, entering a maximum distance