Keysight x-series User Manual

3 Spectrum Analyzer Mode
3.5 ACP Measurement
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
Sample Works well, but never better than Average , because it does not smooth as well
Normal A combination of peak and negative peak behaviors, and works about as well as
these
For best operation, extreme smoothing is desirable, as already stated. Using narrow
VBWs works well, but using very long bucket durations and the average detector
works best. Reducing the number of trace points makes the buckets longer.
For best operation, Average Type = Power (RMS) is optimal (when this option is
available). When making CW measurements in the presence of noise without NFE,
averaging on the decibel scale has the advantage of reducing the effect of noise.
Using NFE with Average Type = Log-Power (LOG) is not synergistic, though; NFE
with Average Type = Power (RMS) works a little better than NFE with LOG.
The results from NFE with internal preamp can often be lower than the theoretical
noise in a signal source at room temperature, a noise density of -174dBm/Hz. This
is expected and useful behavior, because NFE is designed to report the amount of
input signal that exceeds the thermal noise, not the amount that includes the
Spectrum Analyzer Mode User's &Programmer's Reference 1089

Keysight x-series Specifications

General

Analysis Bandwidth	Up to 1 GHz (depending on model)
Real-Time Bandwidth	Up to 1 GHz (depending on model)
Form Factor	Benchtop
Connectivity	LAN, USB, GPIB
Resolution Bandwidth	1 Hz to 10 MHz (depending on model)