The original tracking algorithms were built into custom hardware that became common during World War II . This includes storage tubes used with planned position indicator displays, range height indicator displays, and pen-plotting boards used for civilian air traffic control and waterway management.
2.
The ancillary group originally consisted of an AN / OA-270 Range Height Indicator ( RHI ), and then later upgraded to an AN / OA-929 RHI, which displayed the raw or anti-jam video, and allowed the operator to position the azimuth of the antenna.
3.
Usually they operate pointing to the zenith, but an increasing number of them have nowadays scanning units, that allow to retrieve additional information such as volume information when performing various Range Height Indicator ( RHI ) scans at different angles and at a relatively high speed, and vertical wind profiles, when performing Plan Position Indicator ( PPI ) at few degrees from the zenith.
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