ErikKiekens
New member
Is it true that my boat is highly visible on other's radar screens when my radar is on? So in fact the radar reflector is only useful if my radar is off?
Erik the Chemist
Erik the Chemist
radar reflector
- Thread starter ErikKiekens
- Start date
Vara
Active member
Having your radar on adds nothing to your radar profile as seen by other marine radars.
It may help some ship/ship missiles to home in on your vessel though.
It may help some ship/ship missiles to home in on your vessel though.
st599
Well-known member
No. Another radar will reject the interference from another radar. A reflector may help you be seen but it may not.
SHUG
Active member
NO... the radar signals would have to be accurately synchronised for this to happen. As the emitter/detector array is highly directional it would have to be pointing precisely at you at the moment your radar fired off a pulse in that precise direction. The beam spread is about 2 degrees so that there is about a 1 in 180 chance of that happening if the other radar was not rotating and just facing you. Since both radars are rotating the probability multiplies and there is a 0.000028% chance of the synchronous situation being reached. Phew!!!!
Shug the Physicist!
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Penton Hooker
New member
For all the science that has been presented I remain unconvinced. Long time since I sat glued to a radar screen but when I did, with H.M. Coastguard, it was quite normal to pinpoint a vessel by its radar signal. As I say, long time ago.
CelebrityScandel
New member
There is always someone
.Let me assure you from practice then that for marine radars fitted to commercial and pleasure vessels that other vessels with radars are never visible. Apart from the very good explanation by SHUG they are also frequency discriminated to some extent in that the radar signal is much narrower than the band they transmit within and so they do not all end up on the same frequency, that further reducing the possibility of another radar being visible.
What can sometimes happen is that two radars in the same band will interfere if some sort of synchronisation occurs but this will not make the other vessel visible at all, there will just be an indeterminate interference pattern on the screen.
Somehow, I think you will still not be convinced until you go and try it for yourself. But if you do so please do not rely on us seeing you.
AMCD300
New member
In short - no. However your question is actually a very good one as it alludes to a serious everyday problem for commercial and military radar designers and those who install and maintain them.
It is true that radars can detect the rotating face of another radar 'head' as this can reflect the transmitted signal back to the originating radar, albeit in a very ad-hoc and unreliable manner. It is possible that this is the effect you are alluding to however this should be seen as an interesting side-effect of radar rather than a reliable anti-collision method.
Basically, any flat surface is capable of reflecting a transmitted signal back to the source hence stealth technology using jaunty angles everywhere to reflect the signals in other directions than the source. Much investment has been made in military radar design to reduce the likelihood of this passive (i.e. non-transmitting) detection of radar heads on aircraft.
Interference between two transmitting radars has many causes but a correctly designed and maintained radar should never cause your boat to be visible to another surveillance radar, at least not in the way you mention. I could go into side-lobe interference, detection and suppression but I think that would be a little keen this early in the day
. Anyway interference generally causes different symptoms than a genuine radar 'contact'.Interestingly the issue of like-radars interfering with each other exists for ground-based air traffic control radars where 'sector blanking' (i.e. turning the radar transmitter off at a certain part of its turning cycle) is often used to overcome the problem. This has more to do with transmitted power than frequencies etc but the symptoms are equally problematic.
There has also been a lot of news in the press recently about the effect of wind farms on ATC, weather and military surveillance radars but again, this is a different type of interference: http://www.crh.noaa.gov/mkx/?n=windfarm. And, no, your yacht-mounted wind vane won't have the desired safety effect...
For those who are really interested in radar theory...http://www.radartutorial.eu/01.basics/rb02.en.html
I found this interesting article about radar reflectors: http://www.panbo.com/archives/2011/07/the_passive_radar_reflector_solution_for_sailboats.html. I have no interest towards promoting this product. The information relating to Radar Cross Section (RCS) of purpose-designed reflectors adds weight to the notion that you need the right kit to get the right results. One good point the article makes relates to making sure you install the reflector at the right mounting angle. Anything which reflects radar emmisions in a direction other than back to the source is acting more like steath technology than a good reflector.
I would stick to a correctly mounted purpose-built passive radar reflector to be safe.
Andy the Radar Man
Simes
New member
Penton Hooker,
It is possible to detect a RADAR system from a second position (think about how RADAR transponders like the "SeaMe" work). These will provide you with a bearing from your position to the transmitting RADAR. if you have a couple of fixed points (ie 2 of these RADAR detectors) then you will be able to triangulate between them and obtain a fix. I am fairly confident that this is one of the many methods used by the CG.
I agree with others about the inability of RADAR to pickup other transmitting RADARs. The two RADAR antennas would have to be exactly aligned, the Pulse frequency, length and repetition rate would also have to be precisely (I mean exactly) matched also.
On rare occasions you can get a small element of interference from other RADAR sets in use. This often appears as a series of "Spokes" radiating out from the centre of your screen. These will not give you any form of fix but will prohibit your ability to detect other targets that have been obliterated by the interference. Check out your set for a control labelled "I.R." or Interference Rejection. Engaging this circuit will remove the interference caused by other RADAR sets in you area. Please do not leave it on as any of the clutter controls (IR, Sea, Rain) will reduce your ability to detect other returns.
If you would like to experience RADAR Interference you might try Portsmouth Harbour on a Saturday morning. Often lots of it.
Whilst you are there you could also try increasing the Range to maximum, you can then also experience the on screen effect of "Side Lobes" these will appear are concentric rings around your vessel at a range consistent with the large targets (Navy Vessels & Tower Blocks). Reducing the range will cure this interesting effect.
Have fun,
Simes
It is possible to detect a RADAR system from a second position (think about how RADAR transponders like the "SeaMe" work). These will provide you with a bearing from your position to the transmitting RADAR. if you have a couple of fixed points (ie 2 of these RADAR detectors) then you will be able to triangulate between them and obtain a fix. I am fairly confident that this is one of the many methods used by the CG.
I agree with others about the inability of RADAR to pickup other transmitting RADARs. The two RADAR antennas would have to be exactly aligned, the Pulse frequency, length and repetition rate would also have to be precisely (I mean exactly) matched also.
On rare occasions you can get a small element of interference from other RADAR sets in use. This often appears as a series of "Spokes" radiating out from the centre of your screen. These will not give you any form of fix but will prohibit your ability to detect other targets that have been obliterated by the interference. Check out your set for a control labelled "I.R." or Interference Rejection. Engaging this circuit will remove the interference caused by other RADAR sets in you area. Please do not leave it on as any of the clutter controls (IR, Sea, Rain) will reduce your ability to detect other returns.
If you would like to experience RADAR Interference you might try Portsmouth Harbour on a Saturday morning. Often lots of it.
Whilst you are there you could also try increasing the Range to maximum, you can then also experience the on screen effect of "Side Lobes" these will appear are concentric rings around your vessel at a range consistent with the large targets (Navy Vessels & Tower Blocks). Reducing the range will cure this interesting effect.
Have fun,
Simes
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jwilson
Well-known member
That ship radars can see your yacht radar when switched on and thus you don't need a radar reflector is one of those urban myths - though belief in it is quite common.
SHUG
Active member
You are of course quite correct.
If you have a fixed broad band continuous receiver where you can slowly change the direction in which it is pointing then you will pick up radar signals as and when you point it directly at the transmitting vessel.
That is different from trying to pick up the signal with the normal rotating sender/receiver where ,only when the transmitter and receiver are directly pointing at each other would that be possible. Since both systems are rotatiing in a non-synchronous way the chances of that happening are low.