Chapter 4 _____________________________________________________ TTY Nonvolatile Setups
VAISALA______________________________________________________________________ 115
These questions define the clutter filters that operate on power spectra
during the DFT-type major modes (PPP, FFT, and RPH). Filter #0 is
reserved as "all pass", and cannot be redefined here. For filters #1 through
#7, enter a digit to choose the filter type, followed by however many
parameters that type requires. For details, see in Section 6.2.5 Clutter
Filtering Approaches on page 203.
Fixed Width Filters (Type 0)
These are defined by two additional parameters. The "Width" sets the
number of spectral points that are removed around the zero velocity term.
A width of one will remove just the DC term; a width of two will remove
the DC term plus one point on either side; three will remove DC plus two
points on either side, etc. Spectral points are removed by replacing them
with a linear interpolating line. The endpoints of this line are determined
by taking the minimum of "EdgeMinPts" past the removed interval on each
side.
Variable Width, Single Slope (Type 1)
The RVP900 supports variable-width, frequency-domain clutter filters.
These filters perform the same spectral interpolation as the fixed–width
filters, except that their notch width automatically adapts to the clutter. The
filters are characterized by the same Width and EdgePts parameters in the
Mf menu, except that the Width is now interpreted as a minimum width.
An additional parameter Hunt allows you to choose how far to extend the
notch beyond Width in order to capture all of the clutter power. Setting
Hunt=0 effectively converts a variable–width filter back into a fixed–
width filter.
The algorithm for extending the notch width is based on the slope of
adjacent spectral points. Beginning (Width-1) points away from zero, the
filter is extended in each direction as long as the power continues to
decrease in that direction, up to adding a maximum of Hunt additional
points. If you have been running with a fixed Width=3 filter, you might try
experimenting with a variable Width=2 and Hunt=1 filter. Perhaps the
original fixed width was actually failing at times, but you were reluctant to
increase it just to cover those rare cases. In that case, try selecting a
variable Width=2 and Hunt=2 filter as an alternative. In general, make
your variable filters "wider" by increasing Hunt rather than increasing
Width. This will preserve more flexibility in how they can adapt to
whatever clutter is present.
Filter #5 Type:3 (Gaussian Model) Win:-1 Spectrum width: 0.200 m/sec
Filter #6 Type:3 (Gaussian Model) Win:-1 Spectrum width: 0.300 m/sec
Filter #7 Type:3 (Gaussian Model) Win:-1 Spectrum width: 0.500 m/sec
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