The radar equipment receiving the ACP and ARP signals has the task of interpreting the signals to correctly label each radar return with the azimuth that it was derived from. To do this it needs to know the number of ACP signals in one revolution of the radar, ie the number of ACP pulses between consecutive ARP pulses – call this X. It can then count incoming ACP pulses and calculate the azimuth in degrees, so that for the nth ACP pulse, the azimuth for the radar is n/X * 360 degrees. The value of X can be calculated automatically by the incoming processor by simply counting the number of ACP pulses observed between two consecutive ARP pulses.
So what can go wrong with ACP/ARP signal handling?
To begin with, what does the position represented by time of the ARP pulse represent? Is it the bow crossing of the ship, for example, or some other angle on the ship, which can happen if the radar has not been correctly aligned with the bow. It is necessary to have a reference point, but it is also necessary to know what that reference point is and, if necessary, apply a correction to adjust the azimuths to a more useful value. In a land-based radar, it is useful...
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