Keysight N9915-90015 User’s Guide 71
DTF (Distance to Fault) Measurements
DTF Measurement Settings
—Press Recall Cable to load a Cable file from the specified Storage Device
—
Storage Device Changes the device used to save or recall Cable files. This
is a different setting from the Save/Recall Storage Device setting. Choose
from Internal (default setting), USB (must be connected) or SD card.
About Cable files
— Cable files are saved to, and recalled from, the Cables folder. If the folder
does not already exist on a USB or SD card, it is created automatically
before storing the file.
— Cable files are stored as *.xml files. Existing cable files that are preloaded
into the FieldFox firmware can be overwritten. Your edited file will NOT be
overwritten when firmware is updated.
—To DELETE a Cable file, use the Manage Files feature. Learn more in
“Manage Files” on page 826.
How the Freq/Loss pairs are applied
When the cable file contains one Freq/Loss pair, that correction value is
applied to the entire displayed frequency span.
When the cable file contains two or more Freq/Loss pairs, the Loss value that is
used is interpolated from the Freq/Loss pairs and the DTF center frequency.
For example, using a cable file with the following Freq/Loss pairs:
The center frequency for the measurement is determined from the
calculated (Stop – Start) frequency values (seen on the second page of
DTF Settings):
The Loss value for the measurement is interpolated from the Freq/Loss pairs at
the Center Freq:
The correction for loss at 5 meters in one direction: 0.18 dB/m * 5m = 0.9 dB.
All DTF measurements correct for loss for travel down the DUT and back, so
double the correction: 0.9 dB * 2 = 1.8 dB.
1 GHz: 0.1 dB/m
2 GHz: 0.2 dB/m
Calculated Start = 2.0 MHz
Calculated Stop = 3.598 GHz
Center Freq = 1.80 GHz
1 GHz = 0.1 dB/m
1.8 GHz = 0.18 dB/m
2 GHz = 0.2 dB/m
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