Tektronix 2715, Руководство пользователя

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Spectrum Analyzer Menus
2715 User Manual
6–29
Ensemble averaging computes the average value of some parameter (peak, mean,
minimum, etc.) of a number of signal spectra. If the nature of the signal does not
change during the period over which the average is compiled, the parameter
being averaged rapidly approaches its mean value. This results in an enhance-
ment of the signal-to-noise ratio without reducing the bandwidth or slowing the
sweep speed. This does not mean you cannot ensemble average continuous
narrowband signals. However, in those cases you can also use video filtering,
which may prove faster and more convenient.
The result of the ensemble average is an estimate of the mean value of the
parameter being averaged. Successive estimates, or averages, will vary from each
other in a random fashion. The larger the number of sweeps averaged, the more
accurate an estimate of the spectral characteristic that is obtained.
19. Select ENSEMBLE AVERAGING by pressing [DSPL] [1].
The Ensemble Averaging menu appears. Items 1 and 2 start and stop the
averaging process. The remaining items specify which values to average,
how many sweeps to average, and where to store the result.
If you are going to store just the one ensemble average, it makes little difference
where you put it. You can use registers A, B, or C, but you cannot store the
average in a register that already contains data. Register D is not available,
because it always contains the current trace. If you plan to use the stored average
as a reference and perhaps intend to subtract it from other spectra, you must store
it in register A. Whichever register is used, it must be cleared before you attempt
to store new data in it or you will receive an error message.
Item 8 of the ENSEMBLE AVERAGING sub-menu is a three-way toggle that
switches among registers in the sequence A, B, C, A ... .
20. Ensure that register A is clear and then repeatedly press [8] until the last
character on the line is A.
You can average a fixed number of spectra or choose continuous averaging.
Continuous averages are used when the mean value of the signal you are viewing
can change slowly with time, when you want to watch a mean value estimate
change in real time, or when you simply wish to continuously monitor a process.
If you select a fixed ensemble size, you can average up to 1024 sweeps. The
parameter being averaged can be the maximum, minimum, max/min, or mean of
the spectral display. Averaging begins when item 1 is selected from the
Ensemble Averaging menu and ends when the N
th
sweep has been completed.
You can also stop the averaging by selecting item 2 from the menu.
Continuous averaging weights older sweeps so that they have a progressively
smaller effect on the average. Each step back in time reduces the impact of a
sweep to 90 per cent of its previous value.