3 Spectrum Analyzer Mode
3.2 Swept SA Measurement
correct relative location on screen. The odd buckets are similar.
–
The Average Detector result depends on the Average Type. To explicitly set the
averaging method, use the Meas Setup, Average Type key.
–
Because they may not find a spectral component's true peak, neither average
nor sample detectors measure amplitudes of CW signals as accurately as peak
or normal, but they do measure noise without the biases of peak detection.
–
Peak detection is used for CW measurements and some pulsed-RF
measurements. For FFT analysis, the highest amplitude across the frequency
width of a bucket is displayed, even if that peak amplitude falls between samples
of the spectrum computed in the FFT process.
–
Sample detection is good for displaying noise or noise-like signals but is not the
best choice for making amplitude measurements of CW-like signals. This is
because:
–
the peak response to a signal can occur between samples. So, unless the Span
to RBW ratio is lower than usual, then the highest sample can be well below the
peak signal amplitude.
–
for the high sweep rates normally used, the peak response of the RBW filters is
up to –0.5 dB. This sweeping error is compensated when using the peak and
normal detectors by changing the overall gain. But the gain is not changed when
in the sample detector, because doing so would cause errors in the response to
noise. Instead, the auto-couple rules for sweep time are modified to give slower
sweeps.
–
When the Detector choice is Auto, the detector selected depends on marker
functions, trace functions, average type, and the trace averaging function.
–
When you manually select a detector (instead of selecting Auto), that detector is
used regardless of other instrument settings.
CISPR Detector Notes
Quasi Peak
This is a fast-rise, slow-fall detector used in making CISPR compliant EMI
measurements and defined by CISPR Publication 16–1–1. Quasi-peak detection
displays a weighted, sample-detected amplitude using specific, charge, discharge,
and meter time constants derived from the legacy behaviors of analog detectors and
meters. It is used for EMI measurements to provide a specific and consistent
response to EMI-like signals.
In the past, Quasi Peak and EMI Average measurements were often made on a linear
display scale (and CISPR standard operation calls for this), because those detectors
only worked properly with signals on a linear (voltage) scale. The X-series
526 Spectrum Analyzer Mode User's &Programmer's Reference
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