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Old 12 December 2005, 19:45   #41
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Quote:
Originally Posted by codprawn
I think the active type take the already transmitted signal and amplify it. They don't actually send a new signal out!!!
If that is the case - which it probably is - then how fast does the circuitry in these units work - ie how fast does the signal get read then amplified and then retransmitted.

If it took a mili-second to retransmit the signal when it bounced back would appear to have come from approximately 300 kilometers further away.

If it took a micro-second the inacuracy would still be 300 meters.

Are the electronics in these things really going quick enough to respond in nano-seconds which is what would be required to maintain accuracy.

Or do they work in a completely different way???
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Old 12 December 2005, 21:05   #42
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http://www.mcmurdo.co.uk/Images/CMS_...s%20manual.pdf

This should make it a bit clearer.
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Old 12 December 2005, 21:22   #43
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A wee bit from the Sea-Me manual.

Quote:
When Sea-Me is required, switch it on at the control box and check that the power LED glows green. Sea-me is now on and will remain in an alert (quiescent) state until it is struck by an incoming radar signal. When it detects such a signal it will amplify it and transmit it and the active LED on the control box will flash red, indicating that you are within the range of the interrogating radar.
Note that you are able to tell that a radar is within range of you even though you don't have radar yourself. Of course, you won't have clue where it is. At a sea-me height of 2 metres it is reckoned that a 25kw radar can see you at 8 miles.
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Old 12 December 2005, 21:58   #44
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Anyone ever heard of the Lokata Watchman? It was a passive radar detector that was handheld - you could tell exactly where a radar beam was coming from.

It was developed around the time of the falklands war and there was a fuss because the MOD said it was not a good thing for the public to have!!!

apparently Kelvin Hughes took them over and called it the Rad Seeker.

I reckon there is still a huge market for such a device and they could be made quite cheaply.
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Old 12 December 2005, 22:13   #45
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Quote:
Originally Posted by codprawn
...I reckon there is still a huge market for such a device and they could be made quite cheaply.
Here's you opportunity, then, Cod. Get a Sea-Me and surround it with metal except for a narrow, parallel sided slot. Stick a compass on the top.
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Old 12 December 2005, 22:17   #46
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Quote:
Originally Posted by jwalker
Here's you opportunity, then, Cod. Get a Sea-Me and surround it with metal except for a narrow, parallel sided slot. Stick a compass on the top.
Why not - been messing with Pringles tubes for ages!!!
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Old 12 December 2005, 22:23   #47
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Originally Posted by codprawn
...been messing with Pringles tubes for ages!!!
Too much information!
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Old 12 December 2005, 22:34   #48
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Quote:
Originally Posted by codprawn
Why not - been messing with Pringles tubes for ages!!!
Putting WiFi through them? If yes - any luck?
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Old 12 December 2005, 22:48   #49
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Originally Posted by Jimbo
Putting WiFi through them? If yes - any luck?
Not too bad but ended up making a dedicated waveguide in the end. There are commercial ones around now cheap enough though!!!

Got a Radio Ham mate to knock me up a tuned magmount aerial which is much better. Bit like this

http://cgi.ebay.co.uk/A-New-7-8dBi-M...QQcmdZViewItem

Be interesting when WiMax takes off - the mobile phone companies etc are scared stiff!!!
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Old 13 December 2005, 09:30   #50
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Quote:
Originally Posted by jwalker
Cool, then they'll stay away from all of us.
No, still not convinced in crowded waters active radar reflectors are a selfish solution to being seen. I think a good analogy is having very bright head lights, great for you but a curse for everyone else

A good passive radar reflector should show a blip on a radar screen proportional to your size, an excessive return make the whole thing a nonsense.
I think the true answer is AIS but not at the prices it currently is Des
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Old 13 December 2005, 10:47   #51
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Quote:
Originally Posted by codprawn
Be interesting when WiMax takes off - the mobile phone companies etc are scared stiff!!!
Why ? they will be the ones operating it.
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Old 13 December 2005, 12:44   #52
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Originally Posted by Nick Thompson
Why ? they will be the ones operating it.
Not in every case although with their clout it may well be true. The problem will come with how the hell are calls charged when everyone is using voice over ip???
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Old 13 December 2005, 15:37   #53
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One thing is for certain - the telecoms providers will not let them selves be out of pocket.

Whether your charged per MB or per Minute or a combination of the two the tariffs will be structured such that they look as attractive as possible to the end user whilst maximising income for the network providers exactly as all the telecoms and isp packages are right now.
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Old 13 December 2005, 15:40   #54
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A lot of places are setting all this up for free though!!! Have you seen what Google are up to for example?

http://www.siliconvalley.com/mld/sil...ley_technology

Plenty of places in the UK doing it as well - could also happen with Wimax.
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Old 13 December 2005, 15:49   #55
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Free !!!! to the end user - but someone is still paying the telecoms companies - in this case it will be google. at some point all this data has to cross sombodies network.

And what do google get out of it - in this case it may just be a a way to boost the companies image even furhter but im sure getting more people to use google and therefore click on google sponsered adds etc etc etc etc etc..... all has its paybacks...
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Old 14 December 2005, 05:23   #56
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garfish is right pbo did a very informative report on radar reflectors, ive studied microwaves and radio frequenices and it was not bollox.... infact escluding active units, its trial and error....

all other radar reflectors return a signal along with your boats own signal, for want of a better way to describe it these wavey signals can sorta crash into each other on the return path, this can have the effect of putting the signals on top of each other and increasing your visibilty, however as the frequency has both positive and negative bits when they crash into each other a negative bit could actually attenuate your original signal and hence make you less visible or make it peak greater but for such a short time ships wont see it..

they are not all crap, it tends to be individual to each boat, any reflector could be great at improving your signal or dog poo on any boat, so its real trial and error, maybe find a mate with a radar and do a test w or w/o

There was a guy that lined his whole yacht with tin foil to increase his visibility and almost made himself invisible due to the angle of the reflected waves etc, they compared him with a non lined and very visible identical boat!! monkey!!

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Old 14 December 2005, 14:42   #57
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Quote:
Originally Posted by roycruse
Free !!!! to the end user - but someone is still paying the telecoms companies - in this case it will be google. at some point all this data has to cross sombodies network.

And what do google get out of it - in this case it may just be a a way to boost the companies image even furhter but im sure getting more people to use google and therefore click on google sponsered adds etc etc etc etc etc..... all has its paybacks...

Yes but look how cheap bandwidth has become these days - get in a 1gb pipe and everyone can use it - damn site cheaper than mobile phones!!!
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Old 14 December 2005, 17:12   #58
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I already have one
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Old 18 December 2005, 14:36   #59
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Quote:
Originally Posted by Scary Des
No, still not convinced in crowded waters active radar reflectors are a selfish solution to being seen. I think a good analogy is having very bright head lights, great for you but a curse for everyone else

A good passive radar reflector should show a blip on a radar screen proportional to your size, an excessive return make the whole thing a nonsense.
I think the true answer is AIS but not at the prices it currently is Des
Des, I know I was making light of this but this next question to you is serious and not meant to be at all cheeky.

Have you experience of active radar enhancers producing an excessively large target on a radar screen? I ask because, normally, the size of the target on the radar screen is largely determined by the scanning radar's beam width and the strength of the return is indicated by the brightness of the target on the screen. Since my radar return is emitted from a small source, I had expected my image on a radar screen to be small and bright. It might be worth knowing exactly how I'm being seen.
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Old 19 December 2005, 11:21   #60
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Quote:
Originally Posted by jwalker
......Have you experience of active radar enhancers producing an excessively large target on a radar screen? ........
Yes But perhaps not excessive, coming back through Hurst Narrows one afternoon we couldn’t understand why we could see three yachts about a mile ahead of us through the window and only one large one on the radar. Once they passed the narrows they went there separate ways and became separated blips again on the radar even though one remained far bigger than the others, someone suggested that this was due to AR. Interested I did a bit of digging
As I understand it active radar, such as SeaMe (63sq.m), paints a larger area of the sea than a passive radar reflector such as an Echomax (24sq.m). This in turn shows as a larger blob on the radar screen.This was certainly backed up by our experiences because although the boats were more or less the same size, on the screen one looked three or four times the size.
The intensity of the blob is down to how much of the signal is returned. The example often used is that a flat surface will give a very good return in one narrow direction only, whereas a sphere will give a poor return in all directions. A good radar reflector tries to works like a flat surface but in all directions.
Again the intensity of the return didn’t look like a yacht it looked more like the Yarmouth ferry
Des
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