3 Spectrum Analyzer Mode
3.2 Swept SA Measurement
Adaptive on, you must issue the commands in the proper order, as shown in the example above
Preset Not affected by Mode Preset, but set to ON at startup and by Restore Mode Defaults
State Saved No
Optimal Detector & Averaging Selections
Note that some measurements do not allow you to switch the Detector type (which
is set by default to Average), so the discussion of detector types here is irrelevant for
those measurements. Similarly, some measurements do not allow you to set
Average Type (set by default to LOG), so that discussion here is irrelevant in those
cases.
The instrument is characterized in the factory (or during a field calibration) with a
model of the noise, referred to the input mixer, versus frequency in each band and
path combination. Bands are 0 (low band) and 1 through 4 (high band) in a 26.5 GHz
instrument, for example. Paths include normal paths, preamp paths, the electronic
attenuator, etc.
In most band/path combinations, the noise can be well characterized based on just
two parameters and the instrument frequency response before compensation for
frequency-dependent losses.
After the noise density at the input mixer is estimated, the effects of the input
attenuator, RBW, detector, etc. are computed to obtain the estimated input-port-
referred noise level.
In the simplest case, the measured power (signal plus analyzer noise) in each
display point (bucket) is compensated by subtracting the estimated noise power,
leaving just the signal power. This is the operation when Detector is Average and
Average Type is set to Power (RMS).
For best operation, AverageDetector (default) and Average Type. = Power are
recommended, as already stated. In other cases, operation is often not quite as
good but still highly effective. Other Detector options, when available, behave as
follows:
Positive Peak The noise floor is estimated based on the RBW and the duration of the bucket using
the same equations used in the noise marker function. The voltage of the noise is
subtracted from the voltage of the observed signal-plus-noise measurement to
compute the estimated signal voltage
Positive Peak is one example of processing that varies with detector to give good
estimates of the signal level without the analyzer noise
For pulsed-RF, Positive Peak can still give excellent effectiveness
FFT analysis does not work well, and does not perform NFE well, with pulsed-RF
signals, so this combination is not recommended
Negative
Peak
Not very useful
Spectrum Analyzer Mode User's &Programmer's Reference 447
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