Radar
Radars have an available range. 24 mile is the most common for normal non commercial use. The scanner should be installed on the mast likely above the steaming light, not on the stern. You or individuals on your deck do not need to be exposed to the radar waves from the stern installation. The radar reflector should be install as high on your shrouds as you can get it. Many sailboaters will use the type which you can raise on a flag halyard when you need it, but the higher permanent installion is desired. Good luck.