Radar reflector.

[ccscott49]

I still need a picture of a octahedral radar reflector mounted correectly and an explanation, to prove to the peeps out here, that all the lifeboat radar reflectors are mounted incorrectly, these are all mounted point up, whioch basically makes them almost invisible to ships radar. Please help me, they will not believe me! /forums/images/graemlins/frown.gif

 

[Talbot]

Radar Reflectors
© 1995 by Jim Corenman, Chuck Hawley, Dick Honey and Stan Honey

Most radar reflectors are variations on the 3-sided corner reflector, also known as a corner cube or a trihedral reflector. The principal echo from a trihedral reflector will be strongest when its "pocket" is oriented directly towards the radar. As the trihedral reflector is rotated off this axis in any direction, the echo becomes weaker, and drops by half (-3 dB) at an angle of 12° to 20° from the axis of symmetry, depending on its specific shape (see fig. 1). With increased rotation, the return continues to drop to almost zero as one of the three sides approaches an edge-on attitude to the radar. When one edge is exactly edge-on, there will be a strong but narrow return, caused by the other two edges acting as a dihedral (2-sided) reflector, or one side acting alone as a flat plate reflector. These returns can be very strong, but so narrow in angle as to have little value.

The classic octahedral reflector is made of three planar circles or squares of metal intersecting at right angles, forming eight trihedral reflectors. In the usual "catch rain" position, one trihedral will face up and one down, and the remaining six are arrayed around a circle, three oriented 18° above the equator, and three 18° below. <font color="red"> This optimizes the return from the "pockets", and avoids the nulls or gaps as best as is possible, but only at a 0° angle of heel.</font>

Considerations of heel angle has led to the "double catch rain" position (see fig.), with one planar surface oriented vertically along the vessel’s axis, and the other two planes ±45° from the vertical. This is not the ideal with no heel angle, but moves towards the "catch rain" position as the boat heels.

 

[ccscott49]

Thank you. Any idea how I can pri nt this to show them? Thanks just what I wanted!!

 

[Talbot]

Just a suggestion, but you might try selecting the print option on the "post extras" at the bottom of the thread!, alternatively you could copy and paste into a word processing programme, if that is not your wish, then there is always "print screen" /forums/images/graemlins/laugh.gif

 

[terryw]

Just put your cursor on the picture and the little box of options should pop-up (Save, Print, email and one other), then just select print.

 

[GBGaffer]

Without wishing to rain on your parade, there is one small problem.

My recollection is that the type of reflector used by the RNLI have 'plates' constructed of a radar reflective material embedded in GRP, and thus have very different polar plots to a 'conventional' octahedral type. This would perhaps explain the unusual orientation.

Cheers

 

[BrendanS]

Why would that detract from how to position a conventional octahedral as discussed and shown?

 

[ccscott49]

These are not RNLI lifeboats, but ships/rigs lifeboats and the reflectors on these are difinitely octahedral 3 plate type as found on a bunch of yachts, the type you haul in the catch rain position in the rigging, these are mounted on poles and a definitely mounted wrong, I know they are, just trying to prove it to these assholes!