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Old 18-03-2009, 13:04   #1
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New to the forum as well

Hello All,

Just joining this forum to be able to answer general questions about JRC gear that you might have.

I've been with JRC for 6 years and have exstensive knowledge of our products.

While I am not a sailboat owner, I spent plenty of years hazy gray and under way so I am most certainly a sailor.

If you have any questions at all about product support of JRC products please let me know.

We are not a supporting vendor for this site, so I would like to shy away from questions about JRC pricing or anything of the sort. I am here to offer a different perspective for product knowledge and also to help out with any questions about JRC product that you own.

Great site guys!
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Old 18-03-2009, 13:12   #2
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How close does an object have to be to be invisible to a boat's radar? How big does something have to be before it will show up on your radar?

Thanks

Michael
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Old 18-03-2009, 13:18   #3
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Michael,

There are a lot of factors that come into play.

What is the object made of?

How high is the scanner mounted on your mast?

As you know, all radars use the same theory. An RF beam is emmitted, bounced of a metal object and returns to the radar.

In the case of some sailboats, you don't have much metal at all. Maybe an engine block, the mast and whatever deck tackle you have. This doesn't provide an enourmous amount of surface area to work with.

The size of an object is not as important as how much metal the object has. Fibergalss, wood, plastic...all these things are invisible to RF. It just passes right through them for the most part. If it does bounce off, it could attenuate the signal to a point that the radar will disregard it as sea clutter or raini clutter.

To answer you question, a radar should be able to see tagets measured inside 1/4 of a mile if the radar is tuned properly.

Once inside that range, visiual navigation and situational awareness need to come into play.

Does that answer your question?
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Old 18-03-2009, 14:45   #4
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Sorta. I guess. Are you telling me that I could hit an engineless wooden (or fiberglass) boat powered by oars or sails in fog cause it would never show up on radar? Say this thing is "attuned" to your 1/4 mile radius -- is it still possible for something to be close enough so to be invisible?
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Old 18-03-2009, 15:25   #5
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What I am saying is that if the vessel had no metal on it at all, in your words "engineless wooden (or fiberglass) boat powered by oars or sails", then any radar out there would have a hard time seeing it.

The principal of radar is reflection of RF from metallic objects.

Now, as for the second part of your question. is it still possible for something to be close enough so to be invisible?

Absolutely. That is why I asked how high your scanner was mounted on your mast.

The installation height of the antenna relates to the maximum detection distance. The higher, the better. However, if it is too high, radio wave energy greatly attenuates above the antenna's vertical beam width (the point -3dB from the peak of the main lobe). As a result, it is difficult to detect a close-in target. Sea clutter also increases. Determine the installation height by taking into consideration the weight, maximum length of the cable, and maintenance after installation.


On smaller boats, we have seen many people mount the scanner in such a way that it points towards the water slightly. They are giving up long range performance (which our small radars weren't really designed for anyway) for better close in target detection.

Remember, you only really have 10 degrees of beam hieght to play with.

I hope this helps.

FROM ANOTHER SOURCE:

Minimum range is a more subtle computation, having to do with the pulse length and processing of the microwave signal but there is also a geometric element, which arises from the shadowed region that lies below the beam pulse.
The vertical width of a typical radar beam is about +/- 15 from the horizontal. If the antenna is mounted at height h, the beam first strikes the water at distance of h / tan (15) feet. For a 30' antenna, this is 30/0.268, 112' or about 37 yards from the antenna. With a 12' antenna this distance is reduced to 44' or 15 yards from the antenna. So on a typical small craft, even one with a high-mounted antenna, this is not really a limitation.
The electrical limitation on minimum range is 164 yards for each microsecond of pulse length. Most radars switch to shorter pulse lengths at lower ranges, with something in the order of 0.12 microseconds being typical for ranges less than 1 mile. This translates to 0.12 x 164 or about 20 yards from the antenna but enhanced signal processing usually doubles this electronic limitation.
The lowest range scale on many radars is 0.25 miles or, 0.125 miles or 220 yards. Often the last 50 yards or so is filled with so much noise that these pulse length and height considerations are not the actual practical limitation to minimum range.
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Old 18-03-2009, 16:09   #6
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Quote:
Originally Posted by JRC Support View Post
The installation height of the antenna relates to the maximum detection distance. The higher, the better. However, if it is too high, radio wave energy greatly attenuates above the antenna's vertical beam width (the point -3dB from the peak of the main lobe).
Do you have a link to picture of what you are saying? I don't understand your language.


Quote:
Originally Posted by JRC Support View Post
On smaller boats, we have seen many people mount the scanner in such a way that it points towards the water slightly. They are giving up long range performance (which our small radars weren't really designed for anyway) for better close in target detection.
But if it tilts slightly down one way -- and that is the direction you get "better close in target detection", then would you not gain what you lost in the other direction, since it would be slightly tilting upwards in the opposite direction?


Not sure if this exchange is totally in the "help" range yet, but it sure is in the "interesting" range!

I do now know I could actually not "see" an object in front of me with radar.

And, no, I do not have a unit yet. I am thinking of buying one.

Thanks

Michael
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Old 18-03-2009, 16:25   #7
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Your right, if you tilt in down in the front it does go up in the back. I'm not saying we recommended this, I was just saying many people have done it.

I don't have a picture of what I am talking about with respect to antenna height.

If you are shopping for a radar right now, I would usggedt that you look into SOLID STATE radars. They don't have magnetrons. It is a revolution in the marine electronics industry.
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Old 18-03-2009, 16:34   #8
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Quote:
Originally Posted by JRC Support View Post
Your right, if you tilt in down in the front it does go up in the back. I'm not saying we recommended this, I was just saying many people have done it.

I don't have a picture of what I am talking about with respect to antenna height.

If you are shopping for a radar right now, I would usggedt that you look into SOLID STATE radars. They don't have magnetrons. It is a revolution in the marine electronics industry.
I know you were not recommending it, but once I thought about it, it made sense that what you gained in one direction would be lost in another direction. But I was really splitting hairs.

It was this sentence that baffled me: "However, if it is too high, radio wave energy greatly attenuates above the antenna's vertical beam width (the point -3dB from the peak of the main lobe). "

Unknowns: "Attenuates", "vertical beam width" and "main lobe". However, I did not mean to put the burden of my radar education on you -- I can do the Wikipedia dance at this point.

Thanks for heads-up about solid state.


Michael
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Old 18-03-2009, 16:39   #9
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Attenuates - To alter an emitted beam away from teh frequency and amplitute of its original carrier wave

Verticle beam width - The direction highth of a beam. Since radar is a directional beam, it must have a size. In our case, that size is 20 degrees.

Main lobe - The shape of the beam as it is emitted from the array.
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Old 18-03-2009, 16:52   #10
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Quote:
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Your right, if you tilt in down in the front it does go up in the back. I'm not saying we recommended this, I was just saying many people have done it.

I don't have a picture of what I am talking about with respect to antenna height.

If you are shopping for a radar right now, I would usggedt that you look into SOLID STATE radars. They don't have magnetrons. It is a revolution in the marine electronics industry.
Solid state radar sounds like the thing to have. I found some website on the subject but found nothing for the cuising comunity. Can you direct me to one?
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Old 18-03-2009, 16:57   #11
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Check out Navico (they are a conglomiration of Simrad, Northstar, Eagle, etc)
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Old 18-03-2009, 17:14   #12
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www.navico.com is a pretty useless site as far as relevant information to this thread. Anything substantive out there?
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Old 18-03-2009, 22:22   #13
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www.navico.com is a pretty useless site as far as relevant information to this thread. Anything substantive out there?
PM sent.
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Old 18-03-2009, 22:44   #14
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Thanks for the information -- that is VERY impressive!! I am surprised -- way surprised -- that there has not been substantive discussion about this new technology. Very exciting!!!
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Old 18-03-2009, 23:04   #15
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I would love to talk about it. Hell, I would love it if my company would make one for this market!

We make one for the IMO indsutry, but it's not the same world.

Broadband radar will be like CRT to LCD. It will change everything.
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