VicS
Well-Known Member
It was all based on practical measurements and all done in carefully controlled laboratory conditions which eliminated unknown or uncontrolled variables.
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Radar reflectors again.
- Thread starter Binman
- Start date
It was all based on practical measurements and all done in carefully controlled laboratory conditions which eliminated unknown or uncontrolled variables.
BelleSerene
Well-Known Member
That's interesting JD. I read it before upgrading useless 2" Plastimo tube to Tri-Lens. Can you elaborate please?
capnsensible
Well-Known Member
Avalook at SOLAS Chapter 5.
https://mcanet.mcga.gov.uk/public/c4/solasv/annexes/Annex15.htm
Not a lot of people know that.
Also
http://www.rya.org.uk/infoadvice/regssafety/pleasurecraftregs/Pages/SOLASV.aspx
Soo, should you end up in trouble, someone, somewhere may go after your 'arris for contravening SOLAS.......
Triassic
Well-Known Member
Note the wording in the above links.
"Regulation 19 para.2.1.7 requires radar reflectors to be carried, where practicable, by ships under 150 GT. For UK-flagged this includes pleasure vessels."
"2.1 All ships irrespective of size shall have:
2.1.7 if less than 150 gross tonnage and if practicable, a radar reflector or other means, to enable detection by ships navigating by radar at both 9 and 3 GHz;"
"Carried" and "Have" do not necessarily mean "Fitted", so as long as you have one on board and can use it if necessary then you should be OK in my view.
"Regulation 19 para.2.1.7 requires radar reflectors to be carried, where practicable, by ships under 150 GT. For UK-flagged this includes pleasure vessels."
"2.1 All ships irrespective of size shall have:
2.1.7 if less than 150 gross tonnage and if practicable, a radar reflector or other means, to enable detection by ships navigating by radar at both 9 and 3 GHz;"
"Carried" and "Have" do not necessarily mean "Fitted", so as long as you have one on board and can use it if necessary then you should be OK in my view.
JumbleDuck
Well-Known Member
Each reflector was measured in the laboratory, as you say, but that was only to establish the radar cross section. They then used theoretical models to predict how reflectors of different cross sections would behave at sea, but didn't do any practical field testing at all. That means that they completely missed effects like motion of the vessel, which means that the orientation of reflectors changes constantly - since RCS can vary enormously with orientation, that matters.
Basically they did a very good job of measuring RCS values and a lousy job of predicting real-life performance. It would probably have got a sound but not sparkling 2:1 as a final year undergraduate project. Curiously enough, it's possible that I taught one of the authors as an undergraduate - I certainly had one who went to Qinetiq to work on radar.
VicS
Well-Known Member
But what they did was to measure the RCS at various orientations. Round a full 360° at various angles of elevation.
Practical field testing would have been all very well if there was any way they could have controlled the conditions and accurately reproduced them for each of the reflectors they tested. Without control of the variables any comparisons would have been meaningless.
Boo2
Well-Known Member
Daydream believer
Well-Known Member
Actually it can ( in special circumstances)add up to more than the sum of the 2.
I have 2 of the 100mm diam Plastisimo ones mounted on my inner shrouds so they are at an angle but one will be more vertical when the boat is heeled. I had ocassion to need the help of the RNLI one dark very rough & windy night & after the rescue the cockswain of the lifeboat came to see what reflectors I had. His comment was how good a signal they had given even though his radar set was old & due for renewal
I then spoke to someone with connections in the navy who had been involved in radar design. He would not give me too much detail but It seems that 2 reflectors mounted one above the other can actually , in certain conditions, exagerate the signal echo
No idea why, but my experience would possibly support that
However, having been nearly run down in the Black Deep by a container ship I now have an Echomax dual band plus AIS transponder
Pete7
Well-Known Member
That was a shame because Qinetiq have certainly carried out practical tests on radar in the past. They chartered my rib for one such trial out in the Eastern Solent about 2005/6 time. They wanted a boat (target) with a low radar signature on which to mount objects. They specifically asked that my rib have its radar reflector Echomax removed so they could mount their own kit being tested.
JumbleDuck
Well-Known Member
Yup, and very interesting that is too. However, the changes in RCS in orientation show that performance predictions based on a static reflector are fairly meaningless.
We call that "doing science".
JumbleDuck
Well-Known Member
Thanks. It's probably hard to do the tests, but not impossible. They certainly shouldn't have presented simplistic theoretical predictions as valid results.
lw395
Well-Known Member
I suggest doing what we use to call in the trade 'Reading Skolnik'.....
JumbleDuck
Well-Known Member
Exactly. Somebody should have bought Qinetiq a copy.
Daydream believer
Well-Known Member
Nothing wrong with the Qinetiq report. It stated what the test conditions were & the results achieved. True they may have made predictions of performance in use, but stated what the perameters were & left it to us to decide on the relevance.
If the testing did not suit people then that is not Qinetiq's fault. They only did a certain series of tests & reported on results.
If others want to consider other conditions ( ie rolling about in a big sea at night) then Ok. But one should not ctiticise the test just because the conditions of test do not suit one.
It is a bit like a new type of front door. If someone tests it for impact, & say what the impact tests were, ( ie a big copper from the drug squad belting it 10 times with a ram) you cannot object to it having no fire resistence if they were not testing for fire resistance or claiming such
If the testing did not suit people then that is not Qinetiq's fault. They only did a certain series of tests & reported on results.
If others want to consider other conditions ( ie rolling about in a big sea at night) then Ok. But one should not ctiticise the test just because the conditions of test do not suit one.
It is a bit like a new type of front door. If someone tests it for impact, & say what the impact tests were, ( ie a big copper from the drug squad belting it 10 times with a ram) you cannot object to it having no fire resistence if they were not testing for fire resistance or claiming such
JumbleDuck
Well-Known Member
The tests were fine. The predictions were rubbish. Unfortunately, far too many gullible people accept the predictions without reservation. They would have been better not to publish them.
lw395
Well-Known Member
I don't know how that should be apportioned between the MAIB and Qinetiq TBH.
The MAIB report also concluded that nobody should wear photocromic specs at night, which is possibly a simplistic extrapolation of the facts.
Maybe they just don't understand the dynamic range of things like radar and the mk1 eyeball?
JumbleDuck
Well-Known Member
Good point. It may be that Qinetiq would have liked to do proper tests but the MAIB wouldn't pay for them.
prv
Well-Known Member
lw395
Well-Known Member
If I told you, I'd have to kill you....
Actually it covers a range of techniques, including modulating the transmit pulse with a code, the receiver correlates the return against the code, rather than just looking for power in band. It allows the transmit pulse to be longer for the same energy, so less peak power is needed. Early in the day for explaining this kind of thing....
prv
Well-Known Member
That sounds an awful lot like what's marketed as "broadband" radar, ie frequency modulated continuous wave.
Pete
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