My radar overlay display can see a target on 6nm bụt it can not see on 4nm range

[linhkienbodam]

Hi,
My Furuno 1834C can see a targets on radar display well but on the overlay display, it can see the targets above 6nm range and can not see the targets under 4nm. What's happened with it. Please help. Thank you
Nick

 

[SilverKing]

linhkienbodam,

A couple of things. Try with your gain set to 75%. Also, what charts are you using? The chart does not seem to be displayed when overlay is selected.