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Radar not showing all targets

Old 07-18-2016, 01:06 PM
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Default Radar not showing all targets

I have a 2006 Furuno Navnet 1934, which is an open array unit on the old navnet platform. Has worked great for the past 4 years until recently.

This past weekend while traveling 100 miles, some targets would show while others would not. For example there was a small island that showed up but then just vanished as I got closer, but I never lost the bouy or the rocks it was marking at the tip of the island.

Occasionally I would also have a straight line show up from center all the way out and then disappear. I could see some boats at 1mi, but not the boat that was 30yrds from me.

I adjusted gain, turning down rain/sea and noise rejection on a multitude of ranges, even turned it on auto mode. I even took the rods out of the holders. At one point it almost looked like I was picking up my outriggers possibly. In the end nothing really helped. While I typically adjust for conditions this was really strange and I cannot afford to have something like this happen at night or reduced vis.

Anyone ever see something similar? Could it have been weird conditions that limited radar? I was in flat seas, clear, 90 degrees.
Old 07-18-2016, 01:08 PM
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Time to buy a magnetron.
Old 07-18-2016, 01:48 PM
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If you look carefully next time , do you pick up targets much better off the beam than forward and aft? . That would generally be a good clue your array could use wedging to get the 0* center plane of the vertical beamwidth down at least to the horizon at vessel planing attitude. Next time you are out & at cruise attitude, observe approx. what wasted % of the maybe 25* vertical beam is pointed at the sky forward and sea aft. .

Keep clutter & noise controls at 0 until needed, gain up.

Magnetron sets all had substantial "main-bang" range area a ways at & out from the boat position where all targets of any size would disappear. It was about 1/8 nm with my old radar and that was very disturbing.
Don't know about your Furuno in that respect.

Except for newer 'broadband " radars most radars blank out the area close to the boat . But my new broadband Simrad 4G radome with substantial wedging so it is noticeably angled down at idle attitude & will display smallish targets just a little farther away than I could reach out and touch them. I used a small mast so the forward beam is not obstructed at all ( tower supports aft not on the display). .
Old 07-18-2016, 02:51 PM
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Unless the radar has been physically moved or hit, I don't think wedging is the answer since I can usually see targets perfectly to less than 1/8 mile.

Anyone know of a tell tale symptom of magnetron issues I can point to since I can still see some targets. I also thought the magnetrons went for like 3000 hours vs my 800 on the boat.

My wife did accidentally grab the cord on the hardtop but I can't imagine that would do anything except kill it completely if it was an issue.
Old 07-19-2016, 08:54 AM
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I had a similar issue with my Raymarine radar. I was almost certain the magnetron was shot. It turned out to be one of the settings that I leave on "auto" had been manually adjusted improperly. I'm sure it was my fault but I sure don't remember doing it. Perhaps you might want to do a factory reset to be sure all the settings are set properly before doing anything drastic.
Old 07-19-2016, 09:41 AM
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Originally Posted by lisstriper View Post
Unless the radar has been physically moved or hit, I don't think wedging is the answer since I can usually see targets perfectly to less than 1/8 mile.

Anyone know of a tell tale symptom of magnetron issues I can point to since I can still see some targets. I also thought the magnetrons went for like 3000 hours vs my 800 on the boat.

My wife did accidentally grab the cord on the hardtop but I can't imagine that would do anything except kill it completely if it was an issue.



Maggies can display various symptoms. The last time I thought our Maggie had gone bad it turned out there was about 3 gallons of water in the array.
Old 07-19-2016, 10:15 AM
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I would have a certified Furuno technician check it out.

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