Radar Cross Section

[Dockhead]

Originally Posted by a64pilot

Not nearly as much as people would like to think, see the tests, most reflectors are pure junk. It has a lot to do with cross sectional area, and most sailboat reflectors are just too small to be effective.
If you want to increase your signature you need a transponder, an active reflector if you will.
Think of a Radar reflector as a light reflector and your searching to see something with your spotlight, a reflector helps, but someone shining a spot light back at you will be seen for sure, that is what a transponder does.

I went the active AIS route under the belief that anything likely to be enough to run me over, is likely to have an AIS themselves, and we will see each other.

This.

If you read the tests (a good one was in Practical Boat Owner a few years ago), most of the radar reflectors are, indeed, as A64 said, pretty worthless.

It is worth, however, putting one up -- just make sure it is one of the few that actually does anything.

Better yet is an active one -- Sea Me and so forth -- but those are expensive and require power.

AIS is your best bet, although this does not entirely replace being seen on radar. Get one of the new Class B SOTDMA transponders, but most importantly -- invest in a good antenna, well installed, with good cabling. Antenna is 90% of the performance of any radio

THis is a really important question. Plastic boats are really hard to see on radar, and not being seen is really dangerous.

[TreblePlink]

Originally Posted by a64pilot

Not nearly as much as people would like to think, see the tests, most reflectors are pure junk. It has a lot to do with cross sectional area, and most sailboat reflectors are just too small to be effective.
If you want to increase your signature you need a transponder, an active reflector if you will.
Think of a Radar reflector as a light reflector and your searching to see something with your spotlight, a reflector helps, but someone shining a spot light back at you will be seen for sure, that is what a transponder does.

I went the active AIS route under the belief that anything likely to be enough to run me over, is likely to have an AIS themselves, and we will see each other.

I'm familiar with Radar transponders for aircraft, having repaired them in a past life - primary radar is reflection-based, but to get required range, secondary radar is lower frequency (about 1 GHz) which triggers a transponder reply on a different frequency. A marine radar transponder would need to operate a the same frequency...

[Dockhead]

Originally Posted by TreblePlink

I'm familiar with Radar transponders for aircraft, having repaired them in a past life - primary radar is reflection-based, but to get required range, secondary radar is lower frequency (about 1 GHz) which triggers a transponder reply on a different frequency. A marine radar transponder would need to operate a the same frequency...

https://www.echomax.co.uk/radar-targ...dual-band.html

[IslandHopper]

Originally Posted by TreblePlink

I'm familiar with Radar transponders for aircraft, having repaired them in a past life - primary radar is reflection-based, but to get required range, secondary radar is lower frequency (about 1 GHz) which triggers a transponder reply on a different frequency. A marine radar transponder would need to operate a the same frequency...

We have one of these atop our mizzen, they work very well...

https://www.echomax.co.uk/radar-targ...dual-band.html

[a64pilot]

Originally Posted by TreblePlink

I'm familiar with Radar transponders for aircraft, having repaired them in a past life - primary radar is reflection-based, but to get required range, secondary radar is lower frequency (about 1 GHz) which triggers a transponder reply on a different frequency. A marine radar transponder would need to operate a the same frequency...

I believe it does, and I may have misused the term transponder.
I do not have an active reflector if you want to call it that, but assume one only transmits on response to receiving a signal and doesn't just continuously transmit.
But I'm not sure how one actually works to be truthful, beyond the theory anyway

[IslandHopper]

Originally Posted by Dockhead

https://www.echomax.co.uk/radar-targ...dual-band.html

Snap!

[deblen]

Additional I have learned from practical experience re radar performance:

Many ships carry both X band & S band radars.

X band is what small boats carry. They are useful from 75ft to "some" miles.
The high frequency short pulse of X band is useful for fine detail in harbours & other tight situations. The useful distance is very severely limited by weather.
In average 20+kt conditions,two 65ft fishing boats count on seeing each other at 6-8 nm or less with 10kw 6 ft scanners @ 20ft elevation. High land & big ships can be seen further of course. Again,it comes down to the "squareness" of the targets.

S band is a lower frequency longer pulse radar useful for long distances.
I've never seen one that could display another vessel closer than 1 1/2 miles.
Inside 1-1/2nm,is all clutter,but 120nm is no problem.

Radar can be wonderful,but like all aids,it has limitations. Also,it is very easy to "delete" a target by the operator. The STC/sea clutter & Gain controls are often mis adjusted.

Just my experience. /Len

[Pizzazz]

The typical recreational radar has no problems resolving a sailboat from a few miles away. You just need to play with the settings, especially the gain, rain and STC. Radar is not something that you just leave on. You will either get many strong returns (from waves) or nothing. You need to learn how to use the controls effectively. Best way is to go out of your home Marina on a busy day, paint a few boats with AIS and experiment with the settings to get an idea of the capabilities of your system.

Next, radar range is limited by the curviture of the Earth. For typical sail/motorboat mounted radars you rarely get useful information beyond 8-10 nm. Longer ranges are helpful to identify squalls but for that you need to pay with the rain control as well.

Lastly, do not rely on other boats to see you. AIS helps but you could not be sure the other guys have AIS on or are awake. Use the radar to see them first.

[boatpoker]

Originally Posted by Pizzazz

The typical recreational radar has no problems resolving a sailboat from a few miles away.

Far to sweeping a generalization and often untrue depending on radar setup, weather and sea state conditions, the specific sailboat target in question and it's angle to the radar beam.

[TreblePlink]

Originally Posted by Pizzazz

The typical recreational radar has no problems resolving a sailboat from a few miles away. You just need to play with the settings, especially the gain, rain and STC. Radar is not something that you just leave on. You will either get many strong returns (from waves) or nothing. You need to learn how to use the controls effectively. Best way is to go out of your home Marina on a busy day, paint a few boats with AIS and experiment with the settings to get an idea of the capabilities of your system.

Next, radar range is limited by the curviture of the Earth. For typical sail/motorboat mounted radars you rarely get useful information beyond 8-10 nm. Longer ranges are helpful to identify squalls but for that you need to pay with the rain control as well.Lastly, do not rely on other boats to see you. AIS helps but you could not be sure the other guys have AIS on or are awake. Use the radar to see them first.

Thanks - I have class B AIS, and may have a Radar if I can fix the one I bought cheap.

Human nature is to reduce gain as far as needed to avoid nuisance false returns. As far as Radar distinguishing a boat from waves, I would hope modern radar would average pulse returns, even requiring an echo for two consecutive sweeps before displaying it. Similar noise reduction techniques are now common on oscilloscopes and other electronic test gear.

Too bad the active Radar "transponders" are expensive.

Another low cost approach might be a simple 3 GHz and 9 GHz receiver that warns of being swept by nearby Radar - similar to those used to indicate automobile speed measuring Radar ...

[Wotname]

Originally Posted by TreblePlink

.........
Another low cost approach might be a simple 3 GHz and 9 GHz receiver that warns of being swept by nearby Radar ...... ...

These used to be in the marketplace - dunno if they are still around - never looked for one for decades. Some also gave a rough bearing (+ or- 45 degrees) to the transmitting vessel.

[River Cruiser]

In my experience a 16' aluminum Jon boat shows a better return than a 40' fbglass houseboat. I doubt a sailboat would be much different unless it had a steel or aluminum hull.

[hpeer]

Had a SeaMe. Problem was just when you want it you also want the radar. And my radar would set off the SeaMe.

And another advantage of steel boats!

Earlier this year I was trying to get the radar to pick up a couple of small, 20', wooden fishing boats in about 3' of chop. Damn hard to do. Truth is I would need to be staring at the radar constantly to see them in reasonable time.

[Lodesman]

Originally Posted by deblen

Secondly,a radar reflector is built of cones with 90deg angles to each other & is supposed to be mounted such that the focal point of these cones is horiz. to the water. As shown in the attd.,the cone captures the RF beams,concentrates them into a stronger beam & reflects this concentrated beam back to the T/R antenna.

Not really "cones" - more like pyramids. And the reflected energy is neither concentrated nor focussed. The "plates" of the reflector are mounted 90º to each other, so that an incoming radar pulse will bounce off the first plate, reflect off the second plate and therefore be returned 180º, to the direction it came from. It's ingenious, that each pair of perpendicular "plates" allow 90º coverage, as the angle of incidence of the first bounce is complementary (in the mathematical sense) to the angle of incidence of the second bounce.

[a64pilot]

Originally Posted by Lodesman

Not really "cones" - more like pyramids. And the reflected energy is neither concentrated nor focussed. The "plates" of the reflector are mounted 90º to each other, so that an incoming radar pulse will bounce off the first plate, reflect off the second plate and therefore be returned 180º, to the direction it came from. It's ingenious, that each pair of perpendicular "plates" allow 90º coverage, as the angle of incidence of the first bounce is complementary (in the mathematical sense) to the angle of incidence of the second bounce.

A Radar reflector is a lot like a headlight reflector, they have essentially the same function, as I’m sure a fresnel lens does too, but smooth curved Radar reflectors are hard to make, ones with flat plates are not.
Years ago one of the motorcycling magazines did tests of motorcycles and police Radar, surprisingly almost all of the Sport Bikes had a larger return and therefore were detectable at longer ranges than the full dresser bikes were. Made no sense at first, then someone made the observation that the sport bikes had dual headlights, and back then the reflectors were metal. They removed the headlights and the sport bikes were almost undetectable.