116 Keysight N9927-90001 User’s Guide
Time Domain – Option 010
Time Domain (Transform) Settings
About Velocity Factor and Line Loss
— Velocity Factor is a property of the physical material of a cable. A VF of 1.0
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.
— Line Loss is specified in dB/m (or ft). In addition to the length of the cable,
loss is also directly proportional to the frequency of the signal that passes
through the cable.
The following is an example showing how Line Loss works:
The DUT is a 100 meter transmission cable. The Line 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.
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.
With compensation for the loss using the manufacturer’s specification, the
FieldFox compensates the trace as though the signal traveling through 100
meters was increased by +20 dB. Therefore the response will show 0 dB for
100% reflection.
Data Chain
This setting, available only on the Transform Settings Table, reverts to
Standard when the FieldFox is Preset. Choose from the following:
— Standard – The normal FieldFox data processing chain. Transform
calculations are performed AFTER error correction and trace math.
— 8510 – The data processing chain used by the Keysight 8510 network
analyzer. Transform calculations are performed BEFORE error correction
and trace math. Learn more at the FieldFox Supplemental Online Help
website:
http://na.support.keysight.com/fieldfox/help/SupHelp/FieldFox.htm
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