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These uncertainty curves show how frequency range, DUT Match, and cable loss impact worst-case uncertainty of round-trip cable loss measurements. The uncertainty curves,
separated by frequency range, are shown for DUT Match conditions of 20, 25, and 30 dB. For DUT Match of 30 dB and cable loss of 4-5 dB (reflection measurement of 8-10 dB)
the worst-case uncertainties are approximately ±1 dB.
Uncertainty Curves for Round-Trip Cable Loss Measurements (1-Port)
Round-trip cable loss measurements are convenient for field personnel testing installed cable or waveguide runs. This one-port
technique provides one-way data after twice traversing the cable. The following two sets of uncertainty curves, less than 6 GHz
on the left and greater than 6 GHz on the right, present worst-case uncertainty by DUT Match (i.e., Log Mag) when using
VNA Master for one-port cable loss measurements. As a practical tip, consider using a two-port transmission measurement
technique to improve upon these one-port cable loss uncertainties.
VNA Master (MS20xxC), 5 kHz - 6 GHz
One Port Cable Loss (Log Mag / 2) Uncertainty vs. DUT Match
0.1
1
10
0 1 2 3 4 5 6 7 8 9 10
Cable Loss, Log Mag / 2 (dB)
Uncertainty (dB)
-20 dB
-25 dB
-30 dB
VNA Master (MS20xxC), 6 - 20 GHz
One Port Cable Loss (Log Mag / 2) Uncertainty vs. DUT Match
0.1
1
10
0 1 2 3 4 5 6 7 8 9 10
Cable Loss, Lo
g Mag / 2 (dB)
Uncertainty (dB)
-20 dB
-25 dB
-30 dB