Load Range Mask (LRMSK)

Specified by a TTY setup question , in the range 25 ... 1000 meters.

Any collection of ranges may be chosen from integer multiples of that distance.

See Mt<n> — Transmit sequence #n.

The range mask is passed to RVP10 packed in 512 16-bit words. In each group of 16:

• The least significant bit of each packed word represents the nearest range.
• The most significant bit represents the furthest range.

According to the range bins that are selected in the mask, the signal processor computes and stores internally a range normalization table which is later used to convert receiver intensity levels into reflectivity levels in dBZ.

Note that LRMSK implicitly specifies the number of bins to be processed and output. The maximum bin count is 4200, though depending on the computational intensity of the configuration, RVP10 may be able to compute fewer bins. If the number of bins selected in the bit mask exceeds the maximum, the trailing bins are truncated. If the new mask does not specify any active bins, then a single bin at range 0 is forced on. The default power-up mask selects 256 bins equally spaced by 1.0 km starting from 0 range.

LRMSK determines range averaging. The upper byte of the command controls how many consecutive bins are grouped together. For example:

• 0: No averaging

  For example, if 100 bits are selected in the range mask and no averaging is elected. Then parameters are computed at those 100 ranges, and 100 bins of data are output.

• 1: Pairs of samples are averaged

  If the averaging is to 1, samples are taken at the same ranges, but pairs of bins are averaged together and only 50 ranges would result. Note that the parameters are averaged by summing the autocorrelations for each bin.

  The individual samples that go into each average are taken according to the bits that are set in the mask, except that they are grouped together so that only one net bin results from the several data samples. Note that the limitation of 4200 sampled ranges applies to the bin count prior to averaging.

• 255: 256 terms are summed

The range normalization value associated with the averaged bin is computed according to the midpoint of the first and last sample.

The command discards incompletely averaged bins. Continuing from the previous example, if the averaging were set to 2 so that triples of samples were summed, then only 33 bins would be output. This is because the 100- bit mask left a dangling 100th sample. In the extreme case where there are not enough mask bits to result in even one complete bin, the RVP10 forces the averaging to zero and turns on a single bin at zero range.