2023-SC101-0331 AIS receiver blocking Rev3.pdf

Rev.3 corrects the 26km free space distance calculation at the end of page 3, the effect of adding 35 dB attenuation to a Class B AIS.  Free space is valid for calculating VHF propagation distances less than a kilometer only.  ITU-R P.1546-6 is used for calculating propagation distances greater than a kilometer instead.  Pages 4 and 5 added.  The analysis is otherwise unchanged and the recommendations to IMO NCSR remain valid.

Using ITU-R P.1546-6 Figure 4:

Normal Class B AIS detection range is                     = 28 km = 15.1 nm

Class B AIS detection with 35 dB attenuator is     = 4.2 km = 2.3 nm