Glossary

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A

ATTENUATOR, (ATTN)
In the context of spectral analysis this term mostly denotes an input attenuator. "Attenuator Setting" describes the setting of the "input attenuator".

Decreasing the attenuation by 10 dB results in a
noise floor decreased by 10 dB

AUTO, AUTOMATIC
Automatic coupling of device parameters: AUTO. In order to obtain optimum measurement results the measurement parameters need to be set in a specific relation to one another.

• Resolution bandwidth (RBW), video bandwidth (VBW) and sweep time (SWT) coupled to frequency span (SPAN).
  Background: When parameters are changed, care must be taken not to reduce the ratios of SWT x RBW2/SPAN and SWT x RBW x VBW/SPAN, as this would increase the measurement error.
• Input attenuator (ATTN) coupled to reference level (REF).

This feature allows exact measurements to be made in the majority of spectrum analysis applications within a relatively short time (sweep time) under optimum drive level conditions (mixer level). Automatic coupling should be disabled for special applications such as sensitivity or intermodulation measurements.

AVERAGE NOISE LEVEL
> Noise floor

AVERAGING
A method of smoothing the results of several measurements by combining them and taking the average. Two methods are used:

Noise level with analog averaging:
a lower VBW results in a lower noise figure
(VBW = RBW, VBW = RBW/10, VBW = RBW/100, VBW = RBW/1000)

• Analog (or time-constant) averaging, which is the weighting of the level display by means of the video filter time constant.
  Background: This averaging will occur as soon as VBW is set to a smaller value than RBW. In order not to increase the measurement error, the sweep time must be increased.
• Digital averaging, which is the formation of the average of several sweeps from the stored level values for each measurement frequency.
  Background: This method does not affect the sweep time. However, this measurement principle bears the risk of major measurement errors.

Spectrum without averaging

Spectrum with digital averaging

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