User's Manual

RVP8 User’s Manual
October 2005
TTY Nonvolatile Setups
3–13
Fixed Width Filters (Type 0)
These are defined by two 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 RVP8 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.
Gaussian Model Adaptive Processing (GMAP) (Type 2)
This type of processing is the most advanced form of clutter filtering and moment
estimation (see Section 5.2.5 ). For GMAP processing, the only thing that needs be
specified is the spectrum width of clutter. Note that the algorithm is not too sensitive
to the exact value of this. Several widths should be configured to cover the antenna
rotation rates that are commonly used. It is useful to turn off clutter filtering (select
the all pass filter #0) and then look at actual measurements of the clutter width while
the antenna is rotating, e.g., using the ascope utility or application software such as
the SIGMET IRIS system.
Whitening Parameters for Tx:Random
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Secondary SQI Threshold Slope:0.50 Offset:–0.05
The two values in this question define a secondary SQI threshold that is used to
qualify the LOG data during Random Phase processing. The secondary SQI level is
computed by multiplying the primary user-supplied SQI threshold by the SLOPE,
and adding the OFFSET. See also Section 5.7.3.
Limits: SLOPE: 0.0 to 2.0, OFFSET –2.0 to 1.0