Keysight N9912A User Manual page 33

 Then
 Then
 OR
 Press
 Then
 Then
These settings specify the minimum and maximum frequencies to be used for the
DTF measurement. These exact frequencies may not be used, but a narrower
frequency range may be used that will still pass through the bandpass filter.
To see the frequencies that are used in the DTF measurement, press Meas Setup 4
then
determine the exact frequency range being used.
Coupled Frequency
When a Return Loss & DTF measurement is present, this setting allows you to have
different frequency ranges for each measurement. Learn more on page 26.
Cable (Correction) Specifications
By default, the FieldFox does NOT correct DTF measurements to account for the
inherent loss of a cable. However, to make more accurate DTF measurements, the
Cable Loss and Velocity Factor values should be considered.
About Velocity Factor and Cable Loss
The following is an example showing how DTF cable correction works:
The DUT is a 100 meter transmission cable. The Cable Loss value is .1
dB/meter. This means that a signal traveling ONE WAY through the cable will lose
10 dB of power (100 m * .1dB/m). Because the FieldFox performs this measurement
with 1 port, the test signal travels down the cable and then back, for a total loss of
20 dB.
After a calibration has been performed, for the purpose of illustrating this point,
connect an OPEN to the end of the cable – a maximum-sized fault - for 100%
reflection of the 300 MHz test signal.
Without compensation for the loss of the cable, a –20 dB response would be visible
at 100 meters, which is the OPEN at the end of the DUT. This is from 10 dB of loss
through the cable in each direction.
DTF (Distance to Fault) Measurements
and type the start frequency to use for the DTF
Min Start Freq
measurement.
and type the stop frequency to use for the DTF
Max Stop Freq
measurement.
More
and type the frequency range to use for the DTF
Max Freq Span
measurement.
Center Frequency
DTF measurement.
then Page. The calculated Start and Stop frequencies
Settings Next
Velocity Factor is a property of the physical material of a cable. A VF of 1.0
o
corresponds to the speed of light in a vacuum, or the fastest VF possible. A
polyethylene dielectric cable has VF = 0.66 and a cable with PTFE dielectric has
VF = 0.7.
Cable Loss is specified in dB/meter. In addition to the length of the cable, loss is
o
also directly proportional to the frequency of the signal that passes through the
cable.
and type the center frequency of the range to use for the
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