Calculated Dtf Values; About Alias Faults - Keysight N9912A User Manual

DTF (Distance to Fault) Measurements
DTF Measurement Settings

Calculated DTF values

Press
Values noted on the FieldFox screen with c - <setting>
Start Frequency – Start frequency that is used to calculate DTF.
Stop Frequency – Stop frequency that is used to calculate DTF.
Range Resolution. Indicates the accuracy of the distance to fault
measurement. For example, with range resolution of 500 mm, if the distance to
fault is 10 meters, this value could be inaccurate by +/- 500 mm or between
9.5 to 10.5 meters. This value is calculated from frequency span / resolution
(points).
Response Resolution, not displayed, indicates the distance that could be
between two faults and still show as separate faults. Learn more in
Settings" on page
Maximum Distance. The distance that could be viewed with the current
settings. Defined by: Vf *c*Points/(2*Bandwidth) where:
— Vf = velocity factor
— c = speed of light
— Points = resolution
— Bandwidth = frequency range
Alias-free Range (On/Off)
— On = No Alias images
— Off = Alias images may appear in the response.

About Alias Faults

An alias fault is not a true device response. An alias fault appears because of
the method used to convert frequency to time.
On the DTF Settings page (above) the c - Alias-free Range = Off setting
indicates alias images MAY appear on the screen.
Shorter stop distances (less than 10 meters) and a higher resolution (1001
points) will be more likely to result in Alias-free Range = Off.
When the Alias-free Range = Off, the following procedure will help to
determine if a response is true or an alias response:
1. Put a marker on the response in question and note the distance to the
fault.
2. Change the start or stop distance.
4- 26
Next Page on the DTF Settings Table to view the following calculated
4-25.
Keysight N9912-90001 User's Guide
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