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Radar image not acurate??

Old 10-05-2011, 02:37 PM
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Default Radar image not acurate??

I'm really not sure how to word the issue I am having. Though I'm sure it's an adjustment.

The targets on my radar are off by a few degrees. For example if I run the chart and radar side by side and I am just offshore the land image on the radar will be different from the chart. The land image on the chart might be at a 90 degree line and on the radar it might be at say 70 degrees.

I am assuming the chart is accurate because it is via GPS.

I have looked in the manual for this but I can't find anything, but maybe it's because I don't know what I am looking for.

This is a Furuno NavNet VX2 with a 24" radome.
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Old 10-05-2011, 02:50 PM
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Originally Posted by ScarabChris View Post
I'm really not sure how to word the issue I am having. Though I'm sure it's an adjustment.

The targets on my radar are off by a few degrees. For example if I run the chart and radar side by side and I am just offshore the land image on the radar will be different from the chart. The land image on the chart might be at a 90 degree line and on the radar it might be at say 70 degrees.

I am assuming the chart is accurate because it is via GPS.

I have looked in the manual for this but I can't find anything, but maybe it's because I don't know what I am looking for.

This is a Furuno NavNet VX2 with a 24" radome.

If you would have said 1 or 2 degrees, I'd said not to worry but 20 degrees! I'd check first to make sure your GPS is set up correctly. You may a magnetic drift error set incorrectly or could be using the wrong datum.

BTW, there are many cases where the charts are actually incorrect and the errors have been carried over for years and years.

The radar is only showing you whats there unless you've got it being interpreted somehow.
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Old 10-05-2011, 02:54 PM
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You may need to off set the radar by a few degrees. Find a stationary object like a marker and head right for it. Look to see which side the target is showing up on the heading line then adjust from there. You will need to go into the menu of your radar under set up. Adjust +/- until everything lines up.
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Old 10-05-2011, 02:58 PM
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I hate to admit it but I was having a similar problem with my HDS-8 and BR24. And finally figured out nearly "all my tools" were within inches of the rate compass. After the "Dohhh" moment subsided, I put the tools in a bucket and started enjoying a high degree of plotter'/radar overlay accuracy.
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Old 10-05-2011, 04:26 PM
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Look for "heading adjust" in the installation manual, you'll need to go through the installation wizard to get there.
It's the 2nd occurrence of "heading adjust" in the installation manual for the 1920 (10.4") display:
http://www.furunousa.com/ProductDocu...%203-23-11.pdf
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Old 10-05-2011, 05:46 PM
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If you have an autopilot I would check the compass offset to an object on a chart before I assume the dome is 20 degrees off. You would notice a dome that crooked
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Old 10-05-2011, 06:42 PM
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If you need to adjust the radar heading, do not select installation wizard to get to this menu. Select installation mode (INST. MODE). With the unit OFF, press and hold the MENU key and then press the power key. After the double beep, you can release the MENU key. After power up. press the MENU key and then SYSTEM CONFIGURATION. There will now be an additional option at the bottom of the list called INSTALLATION something or other (can't remember of top of my head). Press that soft key and then select radar setup and then the next page of radar setup will have heading adjust at the top of the page. The procedure for adjustment is in the installation manual. I assume you do not have compass input to your display? If you did, you could use the radar overlay option so you could view the radar image directly over the chartplotter as opposed to looking at them side by side.

Eric
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Old 10-05-2011, 06:59 PM
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Never thought of looking in the installation manual. I figured that was just about the mechanical set up. But I do see the heading adjust instructions in there.

I will mess with it this weekend. Thanks for the quick answers guys!!!
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Old 10-06-2011, 11:15 AM
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Got it!

And this can be adjusted without entering the installation wizard or installation mode. With the radar active press menu, then radar settings then next page then heading adjust. Turn heading adjust "ON" and you can manually adjust the heading with the knob.

Pretty easy, I feel stupid for not finding it before as I have messed with it countless times while trolling offshore.

Thanks for the replies guys, You made me understand it as I didn't know "heading adjust" is what I was looking for.

fairbank56....you mention radar overlay. That was going to be my next question. In the display options menu I see the overlay option but it won't allow me to select it.'

Any ideas?
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Old 10-06-2011, 11:22 AM
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Originally Posted by ScarabChris View Post
fairbank56....you mention radar overlay. That was going to be my next question. In the display options menu I see the overlay option but it won't allow me to select it.'

Any ideas?
You need a heading sensor to be able to do radar overlay. GPS only calculates your position, not heading. Given two position points, your chart plotter can find your direction of travel, but it's then delayed. A heading sensor gives you the exact heading you are pointed in, and thus the radome is pointed, so it knows exactly how to place the radar overlay on the chart.
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Old 10-06-2011, 12:09 PM
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Originally Posted by TheLucille View Post
You need a heading sensor to be able to do radar overlay. GPS only calculates your position, not heading. Given two position points, your chart plotter can find your direction of travel, but it's then delayed. A heading sensor gives you the exact heading you are pointed in, and thus the radome is pointed, so it knows exactly how to place the radar overlay on the chart.
Gotcha, and is this an external component that will plug into the VX2?
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Old 10-06-2011, 12:13 PM
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Never mind I found the heading sensor module.

Thanks
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Old 10-06-2011, 02:22 PM
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You have two settings to get squared away:

1. headng sensor calibration....this is to calibrate the system for accuracy of the rate of heading change....and then

2. Heading Offset....this adjusts for wherever you mount your heading sensor in your boat. For example, mine has to point toward the aft due to mounting interference, so my offset is 180 degrees.

Magnetic declination for true vs magnetic north selection is usually addressed in your nav system.
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