After changing the antenna twice, and then moving a third one to a different location and still having the problem, I called Raymarine directly. They came to the boat in just a few days. When I met them there and started to explain my problem, they stopped me and said that they know what the problem is and have a new antenna for me. They said it was a different type???? Since then it has worked perfectly. The dealer I purchased boat from said he has never had a problem like this, but Raymarine knew about it.