Radar question

Beflyguy · Posted: Mon Sep 13, 2010 12:44 am Post subject: Radar question

After installing a new radar, there seems to be some kind of false images aft that are pretty much always there. I assume this is caused by the post for the anchor light or the GPS receiver but I'm not sure if I just need to raise the GPS or if the 1" diameter post will still cause a problem. Any opinions on this?

colobear · Posted: Mon Sep 13, 2010 1:23 am Post subject:

You might try reducing the gain of your receiver/chartplotter. It would be unusual for a commercially designed setup like your picture shows to create so much interference. Do you see similar false returns from large targets such as slab sided steel ships, etc? Do you see your wake or wave tops in a small chop?

starcrafttom · Posted: Mon Sep 13, 2010 2:28 am Post subject:

what you are seeing is the waves behind you. Your radar should tilt down in the front a little when the boat is at rest. that way when you are bow up your radar is level and showing the water in front of you at closer distance. did you install your self? did you use a shime or spacers on the back bolts? if you have then try adjusting the sea state on the radar.

matt_unique · Posted: Mon Sep 13, 2010 9:46 am Post subject: Gain

I too was thinking of the gain/sea state settings. Your light bar is not causing that return and your unit will "see" about 25 degrees (12.5 down/12.5 up) so unless you are really pointing toward the moon the wedge does not make much difference. (Though I too have a 2 degree wedge because it just felt right).

To give you an example - my radar will paint a HIGH bridge until I am almost going under it.

Beflyguy · Posted: Mon Sep 13, 2010 11:39 am Post subject:

I believe the tower has a 5 degree forward tilt. It doesn't seem to show any waves, even at Neah Bay with 4-6' swells and 3-4'chop. The ghosts seem to be always there, always aft and boats small and large show up well in any direction except the rear where they are lost in the ghosts. I haven't tried adjusting much yet, the settings are on auto but it seems to be working perfectly except to the rear so I figured there must be something that direction that is causing the problem. The GPS antenna top is about level with the top of the radar.
By the way, this is a Simrad BR24 broadband radar.

Thanks for the help.

Matt Gurnsey · Posted: Mon Sep 13, 2010 12:03 pm Post subject:

A regular radar won't pick up those supports for the light and Antenna, but the broadband is a different breed, and it may be able to "see" the mounts, and not know what to do with the data it's getting back.

matt_unique · Posted: Mon Sep 13, 2010 12:05 pm Post subject: GPS

Hmmm...well the GPS receiver should never be in the radar line of sight for max effectiveness of the GPS receiver.

I would check with Simrad to see if they can suggest some tuning/configuration. The number is 800-628-4487

Beflyguy · Posted: Mon Sep 13, 2010 1:52 pm Post subject:

Good idea to call Simrad. Talked to Brian there and he was very helpful. He suggested I first update the software for the chart plotter and the radar.

I also asked about a randomly intermittent sounder which he suggested might be an air bubble in the transducer liquid chamber.

hardee · Posted: Mon Sep 13, 2010 3:20 pm Post subject:

Are those patches always in the same place? Even with the boat out of the slip and away from the pilings? The patches look like piling posts lined up, or like something close, tall and moving across the signal.

Harvey
SleepyC Moon

Beflyguy · Posted: Mon Sep 13, 2010 5:46 pm Post subject:

Sea Angel · Posted: Mon Sep 13, 2010 6:01 pm Post subject:

I wonder if that could be coupler noise since it stays in the same relationship with the rotation. My first impression was that of a beacon, but the garage thing has me with a bunch of ?????s.

What is the relationship with a change of range? Does the display change positioning?

Art

seabeagle · Posted: Mon Sep 13, 2010 9:25 pm Post subject:

Looks like waves to me as well. Our 16 has it's tipsy days on the water and shows waves blinking in and out with the Garmin.

Almas Only · Posted: Tue Sep 14, 2010 6:07 am Post subject:

Unbolt the radar antenna, rotate it 90 degrees, and reattach. Then turn on the radar, and see if the pattern is still shown to the aft on the display screen (namely, at 180 degrees), or if it now shows at 90 or 270 degrees. Then put the antenna back to it's original position, and rebolt.

If the pattern still showed to the aft, you've eliminated the gps/anchor masts and antennae as a source of the problem. If not, try turning the anchor lights and gps on and off (kill all power to each, which might require pulling the fuse for the gps), and see if that makes any difference in the patterns. If so, you've identified the source. If turning them on and off doesn't matter, I have one more idea.

Since the pattern shows while the boat is out of the water, it doesn't seem like there's much point in considering wakes, or other water effects, as a possible source.

Let us know what happens.

Beflyguy · Posted: Wed Sep 29, 2010 12:55 am Post subject:

Following the above advice, I unbolted the radar dome and rotated it a few degrees. The ghosts seemed to turn as I rotated the thing so I concluded that the mast for the GPS and anchor light was causing the problem.
I removed the mast and built a base for the antenna and mounted the anchor light on top of the dome. No more ghosts! I don't know if this issue is exclusive to the broadband radar, but it seems to work beautifully now.

Almas Only · Posted: Wed Sep 29, 2010 6:16 am Post subject:

Glad the ghost problem is solved. I like the new anchor light location on top of the radar dome. I'm in the process of doing the same thing, although my dome is a little too flexible for the heavier light fixture that I'm using, so the attachment will be on the "semi" vertical face, rather than the top. Looks like you're using the lighter weight plastic light, which is my next step if the vertical mounting doesn't work out.