Procedure and Results
The clip antenna was mounted on a 2.5m round wooden stick. Thus, the antenna base was about 4m above sea level.
The AIS stick receiver was connected via USB hub to the notebook and the data was visualized in OpenCPN with CM93
maps. The results are shown in the screenshots below. The
level of map detail has been reduced to highlight the relevant information of the range test.
The web page www.marinetraffic.com displays live AIS data. The screenshot below compares the received data of the AIS stick with the data at Marine Traffic. The red circles in this case correspond to a radius of 5NM.
The receipt rate up to 20NM is very high. At longer ranges, some AIS targets are no longer received, but this is generally observed for all wireless connections, since radio signals are superimposed by noise sources such as cellphone towers or radio station and not arrive
correctly at the receiver. In this case, the smaller the input power at the receiver (i.e. the greater the distance of the AIS transmitter), the greater is the impact of the interference source on the wanted signal.
AIS sends messages repeatedly and in very short intervals, thus occasionally lost data is not problematic.
As the results show below, distances up to 490 NM (AtoN), 215 NM (Class A) and 98 NM (Class B)
are possible. However, it is noted, that in particular AtoNs,
base stations and Class A transponders use high transmission power (> 12.5W), hence the achievable
range is much higher as compared to Class B transponders (2W). Mostly the antennas of AIS stations
are mounted 20m or more above sea level, which significantly affects the possible distances. Ranges of 490NM
are not typical, especially since AIS radio works on line-of-sight. Such ranges may occur due to
atmospheric reflections. AIS is used primarily for
collision avoidance, where the real benefit is limited to 5 to 10NM. The test shows however,
that the world's smallest dual-channel AIS receiver delivers remarkable reception quality.