Furuno 841 Radar range problem

[barneyanddiane]

I have recently installed a second hand Furuno radar. Model 841 Mk 2 with a RSU0071 dome.

I followed the setup instructions and have all settings on auto.

I get a good picture on all short ranges up to 1.5 miles, but from 3 miles and higher I get no echos from any targets. Even turning down the gain manually I get not signal at all.

Any clues as to where to start looking ?

[speciald@ocens.]

Turn up the gain manually. How high is your antenna?

[barneyanddiane]

The antenna is mounted on the mizzen, so about 30 foot high.

I have turned the gain to full. Lots of clutter on all ranges up to 1.5 miles, but almost clear on all ranges from 3 miles and up. There is evidence of the radar sweeping at these ranges as there is a very small circle created at the centre of the display, but no other signal even with full gain.