Bird Technologies SA-6000XT-Manual - Manual (Page 43)

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Data Points -
Increasing the number of data points increases 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). When changing the number of
data points measured, the software automatically recomputes the new maxi-
mum measurable distance. If a maximum distance is entered manually, be sure
to select the data points before entering the max distance. Changing data points
does not turn calibration off.
Frequency Span -
Narrowing the frequency span increases the measurable
distance (refer to the Fault Location Distance Tables, page 91).
Velocity of Propagation -
The velocity of propagation 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 being used.
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 causes the Site Analyzer to
calculate and enter the required frequency span.
There are two methods to determine the frequency span (for both methods, the
maximum distance, velocity of propagation, and number of data points need to
be known). Instructions for both methods are in Step 2 below:

See “Fault Location Distance Tables” on page 91.

Calculate the frequency span.
1. Enable the Measure Match Mode. See “Selecting the Measure Match
Mode” on page 13.
2. Determine the frequency span.
3. Choose how many data points are wanted to measure.
4. Choose a velocity propagation percentage that is closest to the cable in the
system. See “Fault Location Distance Tables” on page 91.
a. Read down the Vel Prop percentage column to determine the fre-
quency span or the maximum distance.
Note: When choosing a distance, choose one that is approximately
25% more than the tower height (or length of the cable system to be
tested).
Example - For a cable with a dielectric constant of 2.296,
the velocity percentage is 66%. If the cable system is 100
feet long, and 238 data points are chosen, then the Site
Analyzer should be set to a frequency span of 700 MHz. The
resolution of the graph will be 5.6 inches.
Note: To avoid potential false “spikes” (aliases) on the trace, be sure
to select a distance that is at least 25% greater than the length of the
cable system being tested.