3 Spectrum Analyzer Mode
3.8 Spurious Emissions 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
More Information
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 get 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 the detector is Average,
and the Average Type is set to Power.
In other cases, operation is often not quite as good but still highly effective. With
peak detection, 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. The peak detector is one
example of processing that varies with detector to give good estimates of the signal
level without the analyzer noise.
For best operation, the average detector and the power scale are recommended, as
already stated. Peak detection for pulsed-RF can still give excellent effectiveness.
FFT analysis does not work well, and does not do NFE well, with pulsed-RF signals,
so this combination is not recommended. Negative peak detection is not very useful,
either. Sample detection works well, but is never better than the average detector
because it doesn’t smooth as well. The Normal detector is 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 will make the buckets longer.
For best operation, the power scale (Average Type = Power) is optimum. 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. When using NFE,
Spectrum Analyzer Mode User's &Programmer's Reference 1489
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