I have a AIS 650 with a dedicated antenna. The range for receiving other AIS transmitters is less than 6 miles in open water. Is this consider normal performance? If not what is causing this marginal performance
This is indeed normal. Unlike VHF radios, AIS transceivers, particularly Class B AIS transceivers, are designed to transmit at very low power (2W). Power and antenna height are the two primary factors limiting transmission range.