AS 680/682
Description, Operation and Maintenance Record and Replay
ADS−B
4−75Ed. 10.07
4.6.5.4 RAC Notebook Page ’CPR Decoding’
The ’Replay Raw Data Send Asterix Data’ tool decodes raw data input. If the downlink telegrams are
extended squitters (DF 17, DF 18 or DF 19) or of downlink format DF5 or DF21, the content of the
telegrams is at least partially decoded. The extended squitters can be position squitters, which are
encoded with the help of the so−called Compact Position Reporting (CPR). The present notebook
page (see Fig. 4−103) is called CPR Decoding, because the prevailing part of the options concern
the CPR decoding. Other options concern validity checks related to the decoded position squitters.
Fig. 4−103 RAC, page ’CPR Decoding’ (example)
The following parameters are provided:
S The locally unique CPR decoding needs a reference position to calculate target positions from po-
sition squitters (airborne or surface). It is possible to choose a Ground Station position or the last
valid target’s position as reference. If the Ground Station is selected as reference location, then
the Groundstation position in latitude / longitude must be entered into the corresponding fields.
S It is possible to enable or disable separately the decoding mode of airborne position or surface
position squitters. The selection of ’Globally unique’ or ’Local’ decoding are applicable for airborne
and surface position squitters.
S Check on mandatory ASTERIX CAT 21 fields: If the mandatory field check is activated, then AS-
TERIX data may only be sent, if the mandatory fields Data Source Identification, Target Address,
Target Report Descriptor, Time of Day, Figure of Merit, and Position are available and valid (refer
to section 4.6.5.3).
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