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Old 12-04-2014, 04:33 PM   #41
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Since you have already been into the fine adjustments, you probably have the manual. Try checking next to a long straight wall. See if it's constantly a warp near the center. That's adjustable. If it's only on targets from ahead (but not the side or rear) then it's the angle. If it's all targets within the center it should be adjustable. I'll be back in the brain box in a couple hours. I'll look in the furuno manual to see how they are tweeked.
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Old 12-04-2014, 04:42 PM   #42
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The mounting height alone will cause an open array radar to overlook the close in area. Installation instructions for open array systems always suggest high mounting positions, probably somewhat due to the radiation, but mostly to increase their range.

Mounting instructions for broad band will direct you to mount it as low as possible without obstructing the beam so the close in performance does not suffer from the overlook issue, which is partly mounting position and partly a power issue with high output radar systems.

If you tilt the array you will lose your rear view beam angle and increase what we called "backscatter" when I was as radar operator. The amount of power projected causes a bright spot where too much radiation is reflected back into the array. The rougher the water the more radiation reflects back at you and the brighter the display and small targets get lost easily. If you tuned it to see only close in, you could tune out some of the backscatter, but lost your longer range capability.

If you are to turn your radar into a shorter range unit, tilting the angle forward might gain you better targeting if you are also willing to tune your unit for short range use. A better choice would be to add a broadband unit, which might possibly use the same display as your current unit.

Radar is a compromise.
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Old 12-04-2014, 04:55 PM   #43
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This is very timely as I'm just finishing up my radar certification. All radars have a minimum detection distance. "Visibility" based on vertical beam width and antenna height are part of and can result in blind spots. But the more restrictive limit is the minimum pulse time that the radar can emit. When targets are too close, the echo comes back before the transmit pulse turns off, and the echo is never heard. We were taught that the limit is 160 yds, but that makes some assumptions about the fastest pulse time and that may be different for different radars. Anyway, you can't see right up next to you. But if you are that close, even in poor visibility, you should be able to see.
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Old 12-04-2014, 05:04 PM   #44
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I don't think the overlook issues is a big one unless you have a planing boat where the boat lifts up and significantly changes the view from the antenna. In that case there are wedges made to correct the antenna angle.

I'd have to go reconstruct the math, but I think I figured that the visibility limit was something like 2-4x the antenna height, assuming a 20deg vertical beam. Or around 1-2 boat lengths away. If you are using radar to navigate amongst objects 1-2 boat lengths away - well, don't do that.
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Old 12-04-2014, 06:10 PM   #45
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Koden & Simrad 4G Radar at same time?

I don't see 160 yards as a minimum. I routinely can get targets at 200' in front, beside and behind. And this is with my antenna up at 80'. So you may have some erroneous info there. 160 Yds may be the theoretical minimum. BUT having been using RADAR commercially for over 35 years, that has never been an issue.

I would suspect that the RADAR needs to be 'initially tuned' correctly. The mention of using 'auto tune' is suspect. AutoTune is not a replacement for a correctly tuned RADAR.

The installation and Owners manual are where to start. Like you just finished the install. Go out, and find a strong, long, straight target to tune and adjust on. Then find a long wall to run along to check the adjustment. The Furuno installation manual shows: 'Adjustment Sweep Timing' being the center distortion to adjust out first, then MBS.

Have you made certain that the range rings are correct? Accurate? Make sure that something a mile away IS showing a mile away on the screen.

Check those two things out and come back. 1. Range Ring accuracy and 2. that when along a straight long target there is no 'indent or deflection' in the center of the screen.


Anyone know why I can't edit and insert a picture?
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Old 12-04-2014, 06:16 PM   #46
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Koden & Simrad 4G Radar at same time?

Click image for larger version

Name:	ImageUploadedByTrawler Forum1417734881.630606.jpg
Views:	59
Size:	61.5 KB
ID:	35083from the furuno installation manual.

Figured that was better than my hen scratching. The picture represents the boat (in the center) along a long straight target. Sea wall, bulkhead, ship. Whatever. And making sure you don't have these deflections.
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Old 12-04-2014, 10:23 PM   #47
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My range rings are accurate checked them between 2 bridges that are 1 mile apart, I can set it to a 1/8 mile is the shortest distance. I normally run at 3/4 to 1.5 mile range on the river that seems to work best for me. The only long target I've ran by are 1200' tows and there is no warping. I can see my wake on the screen and that is one reason I thought a few degrees forward tilt may improve returns closer to the boat. The only problem I think I have is in the location of objects in relation to where they show on the screen. If a channel maker is dead ahead it appears on the display a few degrees to starboard perhaps 5 degrees at most more likely 2 or 3. This hasn't seemed to be a problem that need to be solved at this time seeing as I'am planning on changing the arch and will adjust it then.
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