28 N9912A FieldFox User’s Guide
o Off No interference rejection and fastest possible sweep speed.
o Minimum The lowest level of Interference rejection.
o Medium The medium level of Interference rejection.
o Maximum The highest level of Interference rejection.
Return Loss Measurements
Return loss can be thought of as the absolute value of the reflected power as
compared to the incident power.
When measuring an OPEN or SHORT, all incident power is reflected and
approximately 0 dB return loss is displayed.
When measuring a LOAD, very little power is reflected and values of 40 dB to 60
dB are displayed.
The minus sign is usually ignored when conveying return loss. For example, a
component is said to have 18 dB return loss, rather than –18 dB.
How to measure Return Loss
Connect the cable or any adapter used to connect the device under test (DUT).
Select Preset then Preset Returns the FieldFox to known settings.
Select Mode then CAT (Cable and Antenna Test)
Then Return Loss (Default measurement).
Press Freq/Dist and enter Start and Stop frequency values of the
measurement.
Press Meas Setup 4 then Settings to make appropriate settings before
calibrating.
Disconnect the cable or DUT and press Cal 5 then follow the calibration
prompts.
Reconnect the cable or DUT.
The return loss trace is displayed on the FieldFox screen.
NOTE If the DUT just measured is a cable, and if you are now going to perform a 1-port
cable loss measurement, save the return loss measurement data to memory.
Doing this allows you to omit steps 10 and 11 on page 30 in the procedure for
making a 1-port cable loss measurement.
1-Port Cable Loss Measurements
While all cables have inherent loss, weather and time will deteriorate cables and
cause even more energy to be absorbed by the cable. This makes less power
available to be transmitted.
A deteriorated cable is not usually apparent in a Distance to Fault measurement,
where more obvious and dramatic problems are identified. A Cable Loss
measurement is necessary to measure the accumulated losses throughout the
length of the cable.
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