Radar Reflector

JasB

JasB

Well-Known Member
Joined
28 Oct 2005
Messages
916
Location
Harwich
Visit site
OK, I know this makes me sound like a real skin-flint, but I was thinking about home-made stuff in general (a sort of un-spoken competition on my pontoon), and I got thinking about radar reflectors. I thought to myself that if you took a two foot piece of two inc diameter pvc pipe, stuffed it full of cooking foil and blanked off the ends (to stop the foil falling out) would that work? (after reviewing this post, I THINK I should be corrected for all the references to "THINKING". not a pastime I am usually accused of )
 
I think it will work - if you pack say 60 x 10ft lengths of tube and lash them side by side like a large fence panel it will probably have a reflective area of about 10 sq.m as long as it is correctly oriented. Ideally you would need to rotate it through 90 degrees at random frequent intervals to relect in all directions.
 
I doubt it. Woudnt it be just like a piece of mast.!!!

But you may be on the right track if the pieces were arranged and cut to a specific size relative to the wavelength of radar it might work. I think this is how the patented ones work.

More to the point has anyone got a circuit diagram, that a fool could follow, to make an active radar reflector. They cannot be that difficult, can they??

Years ago ( 1986) I had an old speed radar detector unit that sent out a beam and set off an alarm if it came accross another radar. It worked over about 3 miles and detected the radars on pedestrian crossings up to a mile away.

A "sea me" must be something similar???
 
Unlike a car radar detector, an active boat unit must transmit as well as detect.... this is high tech microwave engineering, and beyond the capabilities of most amateur hobbyist... would require some fairly specialist kit to build properly....
 
OK, that's one suggestion I won't make, then. I just hope they don't read this forum. /forums/images/graemlins/laugh.gif
 
Whaddaya know, another load of crumpled ally posts.

Most Radar reflectors are based on corners (Three sided edges cut from cube corners, not the ones apprently sliced from simple bi-folded ally sheet). To be fully effective the corners must be sharp and precise (not bent and bashed into a poly tube so that they're out of shape too). The most effective are the Triple Lunaberg lenses and the Cyclops, mounted at masthead with 360 arc of incidence. In all cases bigger is better, the trouble being that small yachts are in the most need of a big reflector and are also least able to carry one.

Transponders are triggered by X or J band radar transmitters, amplify the incident signal and re-transmit. Provided you have enough volts, they will result in a bigger blip on the radar screen, assuming there's someone watching it. ARPA only alerts the watchkeeper and if there is no watchkeeper.................
 
Tests done by PBO some years ago seemed to prove that some reflectors could make boats disappear from radar screens when hoisted. Since the Ouzo accident the marine safety people have promised a report on reflectors. It was promised for 1st May but has now been delayed. It may make interesting reading or could be a fudge when it (or if) it appears.
Allan
 
The question made me think. Would it be worthwhile wrapping foil around the mainsail battens (especially if they are full lenght battens)?
This should usefully increase radar reflective area at height without any penalty of weight or wind resistance of a reflector.
has no one thought of this before? olewill
 
Think about what you are expecting. To get a good radar return, the radar needs to be aimed back at the sender. Anything that sends radar off at a tangent will reduce the signal.
 
[ QUOTE ]
The tests were conducted in SRI’s large anechoic chamber, which measures 20’ x 20’ x 40’.

[/ QUOTE ]

pah!

car.jpg


And the answers to your other questions, er, no not really.
 
Idea. Build one JasB, such as you describe, then test it by asking a friendly radar operator to monitor your target with and without your reflector.

Mind, in ideal 'harbour' situations a decent radar will reflect off a swimming herring gull.
 
I did go through a brief period of wondering, while relining a cabin, about the utility of putting a layer of aluminium foil between hull side and cabin lining. A mix of sloth and not being convinced stopped me from doing so but is there any especial reason why not? Ditto I occasionally wonder about the effectiveness of "silvering" on sail material, even if only partial cover. I can only assume that neither of the above work well enough to bother with, or it would be done.
 
Your radar does nothing to allow other ships to see you.
The only way their radar will be alerted to your radar is through interference, which wont tell them where you are anyway.
 
I do know someone who, caught out in the N Sea shipping lanes in fog, took the Bacofoil from the galley and wrapped it round the boat outside the stanchions.

Aside from looking like an oven ready Fulmar, it apparently had ships calling him on the VHF to identify himself as it made a sizeable return on their radars.
 
A couple of years ago I was on the bridge of a small ship, watching a largish (40') wooden ketch about 2 miles away that was almost invisible on the radar. She gybed, putting the mainsail perpendicular to us and magically her blip strengthened several orders of magnitude and became trackable. Almost any flat surface will reflect a reasonable proportion of microwaves, the trick (as I think Brendan said above) is to make sure it's reflected back to the transmitting ship. For that you really need an omnidirectional reflector. Building your own is easy, an octahedral is three intersecting planes. Bacofoil roound the stanchions would make you as visible as any steel fishing boat, but noisier in a breeze.

If you read the Ouzo report, it is apparent (to me) that the ship was approaching the yacht from astern while she was close hauled, so none of the flat sail surfaces were pointing in the right direction.
 
If the bacofoil trick works, then surely putting a layer in between the hull and the head/cabin lining would have the same effect, as suggested by someone else here..... ?

James
 
You must log in or register to reply here.

Share this page

Top