Passive radar reflector info'

Jeremy, what is an active radar reflector?

 

It's a transponder, a combined receiver and transmitter. The receiver detects the radar pulse and triggers the transmitter to send a much more powerful transmission. Both the receiver and transmitter are connected to an omnidirectional antenna, so they have pretty much the same sensitivity in every direction.

Because the transponder is triggered by a radar signal being received it's also possible to transmit data with the transmitted signal. This was first done during WWII, where the system was known as IFF, Information Friend or Foe, and used to distinguish friendly radar contacts from enemy contacts. The same basic system is used today. In fact it's how the data is displayed on air traffic control radar screens, showing the flight number of each contact so the controllers know which blip is which aircraft.

Maritime data systems (AIS) use VHF coupled to GPS rather than radar, mainly to get better range and because international VHF radio standards were overhauled to include data transmission protocols a few years ago (the introduction of DSC as a part of GMDSS).

 

If you have some evidence please provide it.
If you don't get the planes of the reflector at 90 degrees there will be a reduction in signal. Anything can be made poorly.

If the reflector is made correctly, the RCS engineers at work will be very surprised at your statement.

 

The typical commercial passive marine radar reflector is a placebo

Cigarette manufacturers were "surprised" that their tobacco products were unhealthy.

I've done the experiments myself, with a Davis Echomaster. Hoisted up per instructions in the rigging 45 feet above waterline compared with folded up and in the bilge - zero difference in the return from another boat between 1 and 5 miles away. I threw the reflector away after having flown that placebo for 10,000nm.

There are significant limitations of most of these reflectors, making the return from the engine block far more visible than the reflector. It's all very well coming up with an arbitrary recommended minimum RCS of 2m squared, BUT - - your engine block is returning much more (if you have one). And if your boat's rolling or heeling, it isn't even returning 2m squared anyway. Radar Cross Section alone simply doesn't cut it BTW - you also need to think about the polar diagram and boat roll/heeling motion. Not to mention sea state. And don't even think about ships' crew detuning their radar to get rid of sea state noise (you won't sleep at night).

The tube reflectors like the popular Firdell Blipper that just have a few inches diameter are total garbage. Simply do the mathematics.

See this article for more information about limitations: http://www.yachtingmonthly.com/fileBank/PDF/reflector_performance_ym_june.pdf

Ships’ ARPA systems need more than 50% return to fix a target and keep it locked - most commercial passive reflectors can't even do that. And have pathetic returns anyway.

BTW I'm no usual puke - my degree is electronics, thesis was in microwaves.

You're better off with AIS (reasonably cheap) and an active transponder (not cheap!)

Ray

 

Thanks,
I value actual information, instead of simple statements.

 

Jeremy thank you.

 

I constantly track Longline bouys with my radar. These simple spar bouys have a cheap radar reflector on top. I typically pick them up at three miles in calm seas and one mile in a seaway. Radar reflectors work...dont go to sea without one.

AIS is a good investment but the system dies when your vessel looses power. A reflector requires no power and can be transfered to your liferaft when things go bad.

 

With respect, Ray Thackeray, and with due deference to your apparent knowledge, your statement that "....the return from the engine block far more visible than the reflector." is demonstrably untrue.

Back in the late 90's, when we used our mobile RCS measurement radar (which was a bit of military research equipment specifically designed to measure ship and aircraft RCS) to conduct a number of accurate measurements (at sea) on behalf of PBO magazine we proved, beyond any doubt, that all the tested radar reflectors increased the RCS of the test boat.

Certainly some worked better than others, and I would wholeheartedly support the view that a transponder is far and away the most effective device, but a standard tetrahedral reflector, of an appropriate size for the wavelength and mounted in the correct orientation (i.e. in the "catch water" position) will give a big improvement in the return for the majority of leisure boats.

It's possible that the back issues of PBO with the three articles covering these tests are available as back issues. IIRC they were published around 1998/1999.

 

Echomax 230 is the only commercially available reflector that currently satisfies ISO 8729 according to the report posted by Ray Thackery linked again below:

PDF file : http://www.yachtingmonthly.com/fileBank/PDF/reflector_performance_ym_june.pdf


Here's their website: http://www.echomax.co.uk/Echomax_Products.htm

 

I read the article. Very interesting. Some of these reflector looks like having May West bra on top of the mast. One weight almost 12lbs. I mean we are taking serious apparel here
The Echomax antenna shape seams the most elegant solution.

 

But this isn't a passive radar reflector (as in the title of this thread) at all, it's a radar transponder.

Any transponder will knock spots off a passive radar reflector in terms of performance, but does need power all the time to work. Not a lot, admittedly, but if you lose power then you lose the transponder and so have no effective means of enhancing your radar cross section at all.

I think transponders are pretty good, but I would want to be 100% assured that the power supply to it could never be lost, particularly under the sort of conditions when you might be relying on it to help a SAR asset locate your small boat.

 

Yes it is !

Look at the top of page 3 of the pdf, The Echomax EM230 is a passive device. They consisit of 3 tiers of passive reflectors of a unique design.

The only active device tested was the Sea Me which you'll find on page 7 of that pdf.

 

Quote taken directly from the top of that web link to the product given in the post above to which I referred:

It's obvious from this that the device is an active transponder.

 

The weblink contains the descriptions of several devices, you are quoting the blurb for the ECHOMAX ACTIVE-XS

Look at the Echomax EM230 it's further down on that web page and it's passive, and it's the only passive device tested in the yachtingmonthly report (pdf link) that meets ISO.

 

Would have helped if the web link had been given with a note pointing out that the actual product being referred to was a fair way down a long page full of active transponders. It was less than obvious that the thing referred to was actually there!