Reply
 
Thread Tools Search this Thread
 
Old 12 December 2005, 15:45   #41
Member
 
Country: UK - England
Town: Newquay, Cornwall.
Boat name: None :(
Make: None :(
Length: 5m +
Engine: None :(
MMSI: None :(
Join Date: Jun 2005
Posts: 1,280
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???
__________________

roycruse is offline   Reply With Quote
Old 12 December 2005, 17:05   #42
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
http://www.mcmurdo.co.uk/Images/CMS_...s%20manual.pdf

This should make it a bit clearer.
__________________

__________________
codprawn is offline   Reply With Quote
Old 12 December 2005, 17:22   #43
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
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.
__________________
JW.
jwalker is offline   Reply With Quote
Old 12 December 2005, 17:58   #44
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
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.
__________________
codprawn is offline   Reply With Quote
Old 12 December 2005, 18:13   #45
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
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.
__________________
JW.
jwalker is offline   Reply With Quote
Old 12 December 2005, 18:17   #46
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
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!!!
__________________
codprawn is offline   Reply With Quote
Old 12 December 2005, 18:23   #47
Member
 
Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
Quote:
Originally Posted by codprawn
...been messing with Pringles tubes for ages!!!
Too much information!
__________________
JW.
jwalker is offline   Reply With Quote
Old 12 December 2005, 18:34   #48
Member
 
Country: UK - England
Length: 6m +
Join Date: Sep 2004
Posts: 1,850
Quote:
Originally Posted by codprawn
Why not - been messing with Pringles tubes for ages!!!
Putting WiFi through them? If yes - any luck?
__________________
Jimbo is offline   Reply With Quote
Old 12 December 2005, 18:48   #49
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
Quote:
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!!!
__________________
codprawn is offline   Reply With Quote
Old 13 December 2005, 05:30   #50
Member
 
Country: UK - England
Town: nr Lymington
Boat name: JU-JU
Make: Halmatic PAC22
Length: 6m +
Engine: 140.5 Mermaid
Join Date: Sep 2003
Posts: 1,400
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
__________________

__________________
Scary Des is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 18:54.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.