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R&S FSH
Digital Modulation Analyzer
General Settings of the Digital Modulation Analyzer
Transducer
Shows the name of the transducer if one is in use. For more information see Using
Transducer Factors on page 121.
Ref Level
Shows the current reference level of the R&S FSH.
The reference level is the power level the R&S FSH expects at the RF input. If "Auto
Low Noise" or "Auto Low Distortion" is on, the R&S FSH uses it to determine the
attenuation and preamplification internally.For more information see "Setting the RF
Attenuation" on page 91.
Keep in mind that the power level at the RF input is the peak enevelope power in case
of signals with a high crest factor like LTE.
To get the best dynamic range, you have to set the reference level as low as possible.
At the same time, make sure that the maximum signal level does not exceed the
reference level. If it does, it will overload the A/D converter, regardless of the signal
power. Measurement results may deteriorate (e.g. EVM). This applies especially for
measurements with more than one active channel near the one you are trying to
measure (± 6 MHz).
Note that the signal level at the A/D converter may be stronger than the level the
R&S FSH displays, depending on the current resolution bandwidth. This is because the
resolution bandwidths are implemented digitally after the A/D converter.
In case of an IF overload, the R&S FSH shows a corresponding warning in the diagram
area (
).
If you are not sure about the signal strength, you can avoid an IF overload and
determine the maximum level manually or perform an automatic level adjustment.
► Press the MEAS key.
► Press the "Level Adjust" softkey.
The R&S FSH performs a series of measurements to determine the ideal reference
level for the current signal.
Note that the current signal level does not necessarily have to correspond to the
reference level after an automatic adjustment. This is because the R&S FSH
measures a frequency range that is larger than current span and adjusts the
reference level to the measured peak which may be outside the visible span.
An automatic level adjustment will set the attenuation mode to "Manual" if it has
been set to "Auto Low Noise" or "Auto Low Distortion" previously.
You can also determine the reference level manually.
► Perform a measurement in spectrum mode with the largest resolution bandwidth
(3 MHz) and video bandwidth (3 MHz).
► Activate the peak detector.
The trace maximum corresponds to the ideal reference level.
For more information see "Setting the Reference Level" on page 89.
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