USER’S MANUAL__________________________________________________________________
146 _________________________________________________________________ M211322EN-D
The upper portion of the plot shows the sampling window wherein the
burst pulse is measured. The duration of this window is determined by the
impulse response length of the matched FIR filter. This is because the same
FIR coefficients that compute "I" and "Q" are also used to compute the
reference phase vectors for the burst pulses. The A/D samples of the IFDR
burst input are plotted (somewhat brighter) within the sample window.
The RVP900 computes the power-weighted center-of-mass (COM) of the
burst pulse envelope. This allows the processor to determine the location
of the "middle" of the transmitted pulse within the burst analysis window.
The Pb plot displays small tick marks on the top and bottom of the burst
sample window to indicate the location of the COM. These markers are
only displayed when valid burst power is detected. A second "error bar" is
drawn surrounding the tick mark to indicate the uncertainty of the mark
itself. This error interval is used by the burst pulse tracking algorithm to
decide when a timing change can be made with confidence.
It is possible to independently choose a subinterval of burst pulse samples
that are used by the AFC frequency estimator. Thus, the AFC feedback
loop is not constrained to use the same set of samples that are chosen for
the FIR filter window. The FIR window typically is longer than the actual
transmitted pulse, and thus, the samples contributing to the frequency
estimate will include the leading and trailing edges of the pulse. These
edges tend to have severe chirps and sidebands, compared to the more pure
center portion of the pulse. The AFC frequency estimate (which is power
weighted) could be mislead by these edges and might not tune to the
optimum center frequency if they were included.
The lower portion of the plot shows the triggers that are output by the
RVP900. The number of triggers plotted match the number of user-defined
output triggers set in the Mt menu, with Trigger #1 being at the top. They
are drawn in their correct polarity and timing relative to each other, and
relative to the burst sample window. The sample window is always drawn
in the center of the overall time span. Depending on the PlotSpan and
location of the trigger edges, triggers that do not vary within the plotted
time span appear as flat lines.
The RVP900 defines "Range Zero" to occur at the center of the burst
sample window. This also defines the zero reference point for the starting
times of the six programmable triggers. For example, a trigger whose
starting time is zero is plotted with its leading edge in the exact horizontal
center of the display. Knowing this convention makes the absolute value
of the trigger start times more meaningful.
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