Radar as a Radar reflector????

[Oscarpop]

As I understand it, passive radar relectors have a metal something up the mast which is easier for other ships radar to see.

Active ones produce some sort of electrical signal which makes it easier still to pick up.

Now my question.

Does having a lump the size of a radar halfway up the mast ( as well as an omnidirectional tv antenna at the top) will work similarly is not the same as a passive reflector?

Secondly, if the radar is spun up, does it provide an easier to see target? I am sure I read somewhere that people turn they're radars off to reduce the chance of detection by pirates. ALthough once again I may have dreamt this.

Many thanks.

 

[rob2]

Well... Yes, a passive reflector in its simplest form consists of metal plates interlocked to form internal square corners so that a beam hitting it will be reflected back in all three dimensions, like a billiard ball coming back out of the corner cushions of the table. An active reflector or Radar Target Enhancer detects a strike from a radar and emits a much stronger signal than that received, so it is more reliably received.

A radar scanner does not have the ideal shape to return a signal and may be pointing in any direction when stopped. When working, it would only be detected by the other vessel's radar if it happened to be in perfect ysnchronisation with his, thus sending its own signal back to the scanner to be received as though it were a reflection. It is possible to detect a radar which has painted you, but your own radar is not designed to do this - it is looking out, not listening. An RTE has an LED which flashes whenever it is painted, so you know it is working. Sitting near Southampton it's flashing away like crazy! Radar detectors are not commonly on the market anymore as more sophisticated kit has largely replaced it, but a car radar detector will work with X band, I believe.

On a second issue, commercial shipping uses X band for coastal navigation, same as a yacht might fit, but once turned away from the coast is likely to switch to S band which gives far greater range but has a limited ability to etect a small target, such as a yacht's passive radar reflector. This is why the dual band RTEs were so welcome after years of only X band units being manufactured.

Rob.

 

[snooks]

Secondly, if the radar is spun up, does it provide an easier to see target? I am sure I read somewhere that people turn they're radars off to reduce the chance of detection by pirates. ALthough once again I may have dreamt this.

Many thanks.

The pirates may use a radar detector?....Lokata used to make one in the 80s (Lokata Watchman IIRC), it looked like a torch and you pointed it in a 360 sweep, and with the use of headphones you could hear the pulse from the radar, the closer the angle to the source, the louder the pulse that's heard.

Also RTEs they will flash when they are hit by radar so you know there is a radar user in the area

 

[AntarcticPilot]

As I understand it, passive radar relectors have a metal something up the mast which is easier for other ships radar to see.

Active ones produce some sort of electrical signal which makes it easier still to pick up.

Now my question.

Does having a lump the size of a radar halfway up the mast ( as well as an omnidirectional tv antenna at the top) will work similarly is not the same as a passive reflector?

Secondly, if the radar is spun up, does it provide an easier to see target? I am sure I read somewhere that people turn they're radars off to reduce the chance of detection by pirates. ALthough once again I may have dreamt this.

Many thanks.

Basically, no and no.

1) As others have pointed out, passive radar reflectors are very precisely made pieces of equipment, which present a right angled corner in as wide a range of directions as possible. The right angles have to be quite accurate or the reflection is simply dispersed. The chances of your radar antenna creating a good reflection is negligible; your mast has a better chance!

2) Your radar antenna is designed to take a signal from a radiating element and reflect it into an almost parallel sided beam. Incoming signals will be concentrated on the radiating element; they won't be reflected back where they came from.

Radars and radar reflectors or radar repeaters do different jobs; their geometry and characteristics are quite different.

 

[maxi77]

Basically if you want to make yourself more easily seen by others radar you need to fit a proper radar reflector or an active transponder

 

[lw395]

Basically if you want to make yourself more easily seen by others radar you need to fit a proper radar reflector or an active transponder

Or buy a bigger boat with a nice tall metal mast!

 

[Beadle]

The thing to remember with radar is the time dimension.

When a working radar transmits a pulse it is only a tiny fraction of a second long. The receiver part of the radar then "listens" for somewhat longer period for the reflected pulse - how long does it take to travel 30/40 miles at the speed of light? The reciever then turns off until after the next pulse has been sent.

So the probability of receiving a pulse from a different radar is small enough to be neglected.

As for acting as a passive reflector: the whole design of a radar aerial is to transmit and receive only in a very narrow beam. This means the aerial is designed to "focus" the train of pulses it sends into the narrowest possible beam. This of course works both ways, it is only able to recieve pulses from precisely the direction in which it sends. A degree or two either way and there is nothing.

Add to this the design of the aerial itself. It is designed to work into a load - the radar reciever - and not to carry a standing wave which would effectively re-radiate the power it received.

So I think its a case of nice try but no cigar

 

[maxi77]

Or buy a bigger boat with a nice tall metal mast!

Unless it is an awful lot bigger you will still need some way of making yourself look bigger. The mast itself is a pretty poor radar reflector though it provides a good place to hang things,