What you detect is totally o.k. and normal.This is due to the difference between dynamic and static data. In the AIS radio net there are at the moment 24 different message types existing. The dynamic data of a class B AIS transmitter are sent with the telegram type 18. The static data of a class B AIS transmitter are sent with the telegram type 24. Each telegram, not depending on type length is 25ms. All telegrams are checked internally in the easyTRX, if all the data are received completely. If the checksum is not correct, the telegram won´t appear on the plotter screen.Dynamic data type 18: If the pleasure vessel is faster than 0,1kn the transmission cycle time is 30sec. If the pleasure vessel is at anchor the transmission cycle time is 3min. Dynamic Data content: MMSI, SOG, Position Lat and Long, COG, UTC and TH.
Static data type 24: Not depending on the speed or the vessel, the static data transmission cycle time is 6 min. Static data content: MMSI, call sign, ships name, ship type (37= pleasure boat), dimensions of the ship, pos of the GPS antenna on the ship.
Now the situation is the following: Let’s say the customer gets the first input of dynamic data at 8nm distance. It might take max 6min from that point that the other Class B ship sends out a static data. If there are interferences the customer might not get the static data once. So he has to wait again for further 6min. With the dynamic data, a “lost” of one telegram is not so dramatic, because these are repeated every 30s. With the static data, a “lost” of one telegram is suboptimal, because these are repeated every 6 min.