Tektronix NetTek YBT250, Руководство пользователя

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Displaying a Signal Spectrum
3- 32
YBT250 Field Transmitter & Interference Tester User Manual
Performing a Mask Test
To perform a mask test, select View > Mask so that there is a check
mark next to Mask . The defined mask is displayed, with the mask
centered on the current Measurement Frequency.
If the signal trace exceeds the mask, the violation icon ( )
appears on the right side of the spectrum graph and the violated
mask trace changes color (the specific color depends on the selected
color scheme.
A mask trace does not have to cover the entire frequency range of a
graph. Signal points at frequencies that don’t have associated mask
points are not tested for violations. This allows you to check only
those parts of the signal that are critical to your specific measure-
ment, for example the attenuation in adjacent channels.
Mask Testing and Markers
When Mask testing is enabled, the marker difference readout
displays the difference between the marker and the mask. A positive
value indicates a passed test. A negative value indicates a failed test.
A positive value for an upper limit means that the signal level is
lower than the mask level at the marker frequency. A negative value
means the signal level is higher than the mask level, thus violating
the mask. For a lower limit mask, a positive difference means the
signal level is higher than the mask level and a negative difference
means the signal level is lower than the mask level.
The YBT250 calculates the difference between the marker and the
mask using the above rule to determine the sign of the difference.
The YBT250 calculates the difference between the signal level and
the level of each of the traces in the mask. The YBT250 then
displays the worst case difference between the signal level and all
the traces in the mask.
For example, suppose there are two traces in a mask; one is an upper
limit and the other is a lower limit. The upper limit mask trace level
at the marker frequency is 0 dBm, the signal level is --10 dBm and
the lower limit mask trace level is --30 dBm. Thus, the difference
between the upper limit and the signal level is 10 dB, and the
difference between the signal level and the lower limit is 20 dB.