[firstlight]

2006 36' open   Upgraded from Raymarine open radar to Garmin 24" fantom with a Scanstrut mount 6"
radar set at 3/4 mile, great image until i get close.  Its gets smaller and smaller and as I pass a target ( buoy) approx. 100 ft away it disappears.   
I'm thinking maybe rad dome should be mount higher??   Thanks appreciate any feed back.

[ReelMagic]

Not sure if additional height will help with close in detection as each radar antenna has what is called a vertical beam width (there's also a horizontal beam width) that will process targets within that beam width. Given the vertical beam width for your specific antenna is 25 deg's it's possible you will loose target detection around 100 ft. In your case the buoy falls outside the vertical beam width (to close or under the beam) thus loosing the target (buoy) on your display. A vertical beam width of 25 degs covers approx 12.5 degrees up from the horizontal and 12.5 degs down from the horizontal at the antenna. If you know the height of the antenna you can calculate where the beam can see targets and where it will lose targets as they approach your boat.. Most units start to lose targets around 60-100 ft from from the antenna. Height helps in range mostly. The higher the antenna the farther out you will sense targets, based on antenna power. Size/height of targets as well as your antenna height affect range where targets will be detected.. Curvature of the earth plus antenna height & target height affect detection range .. M2C