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Fig. 4. Conceptual diagram of the digital receiver and down converter indicating the
essential operations. The dashed vertical line shows where digital processing begins.
Fig. 5. Conceptual timing diagram of processes in the digital receiver. The return signal is
assumed to be sinusoidal pulse such as would be produced by a single point scatterer.
3.2.1 Lowest elevation scans
At the lowest two (sometime three) elevations (< 1.6 o ) two consecutive scans at each
elevation are made. For surveillance and reflectivity measurement the longest PRT is used
so that the unambiguous range is ~460 km. It is followed by one or more of the higher PRTs
for measurement of Doppler velocity and spectrum width whereby the unambiguous
velocity interval is larger than ~ 20 m s -1 . Thus Doppler estimates can be ambiguous and
overlaid in range. To determine the location of the Doppler estimates, powers along the
radial at the same azimuth but in the surveillance scans are examined. The echoes from
ranges spaced by n PRT c /2 of the Doppler scan, where n is 1, 2, 3, 4, can be overlaid in the
Doppler scan; the echo for n =1 is said to come from the first trip because it corresponds to
the round trip shorter than the separation between consecutive pulses. Powers from
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