Just a bit of info to share. I recently gave a mate my old navman 5500 plotter but didn’t have the aerial for it. He priced one up at $340 that blew me away so I got on USA ebay and found there is a company in the states that make after market amplified receivers for all makes of GPS including the navman $20 so I ordered one thinking $20 isn’t much if doesn’t work. It arrived in 9 days plugged it in and within a 2 mins full screen of satellites. http://www.gilsson.com they are cheaper through ebay than this site