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#1
posted to rec.boats.electronics
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Microwave leak detector
On Mon, 21 Jan 2008 01:06:06 +0100, Marc Heusser
d wrote: In article , John Navas wrote: http://www.sea-me.co.uk/ ... BTW: Do these (active reflectors) also work if you have your own radar, ie will they make you visible to other vessels? Or is it only possible to use passive ones (90? reflectors, Luneburg lenses)? Never quite figured that out in spite of my MSEE degree :-) Marc It appears from the user handbook that the thing is a radar transponder - on receipt of a signal in the appropriate frequency range, it will transmit a brief pulse on that frequency, which will appear as an obvious mark on the radar screen, just like a RACON. It is independent of your own radar - but must be mounted so that it will not be triggered by your radar. -- Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca |
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#2
posted to rec.boats.electronics
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Microwave leak detector - active radar reflectors
In article .com,
Peter Bennett wrote: On Mon, 21 Jan 2008 01:06:06 +0100, Marc Heusser d wrote: In article , John Navas wrote: http://www.sea-me.co.uk/ ... BTW: Do these (active reflectors) also work if you have your own radar, ie will they make you visible to other vessels? Or is it only possible to use passive ones (90? reflectors, Luneburg lenses)? Never quite figured that out in spite of my MSEE degree :-) Marc It appears from the user handbook that the thing is a radar transponder - on receipt of a signal in the appropriate frequency range, it will transmit a brief pulse on that frequency, which will appear as an obvious mark on the radar screen, just like a RACON. Yes, so much is clear. It is independent of your own radar - but must be mounted so that it will not be triggered by your radar. That is most likely impossible. At a few kW of transmitting power (peak), it will trigger when the distance is only a few metres at most. The question is, whether it still appears on other radars. Marc -- remove bye and from mercial to get valid e-mail http://www.heusser.com |
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#3
posted to rec.boats.electronics
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Microwave leak detector - active radar reflectors
On Mon, 21 Jan 2008 08:49:02 +0100, Marc Heusser
d wrote in : In article .com, Peter Bennett wrote: It is independent of your own radar - but must be mounted so that it will not be triggered by your radar. That is most likely impossible. At a few kW of transmitting power (peak), it will trigger when the distance is only a few metres at most. Marine radars have a limited vertical beam width, and the transponder should be mounted above or below that vertical pattern. See the Handbook: If Sea-me is being fitted elsewhere, say on a radar arch, ensure that it is above the superstructure of the vessel and that it is not within the vertical beamwidth of any radar which may also be fitted. Normally this means that the Sea-me antenna unit must be above or below a 30° line from the centre of a radar antenna but you will need to refer to your radar manual to confirm this. .... Radars have many leakage paths and so Sea-me will respond to your own radar’s pulses (typically a pulse is 1 microsecond long and is repeated every 1 millisecond). The LED flash has been extended to 100 milliseconds to make it visible to the human eye and so it will be permanently on when your own radar is transmitting. However Sea-me transmits in response to an incoming pulse and so it will respond to any which arrive in the spaces between the pulses put out by your own radar. Typically the ratio of space to pulse is 1000:1 and so there are 999 microsecond spaces for every 1 microsecond pulse received, plenty of time for others to get in, even when electronic recovery time has been allowed for. This effect does however mean that Sea-me, because the active light is on, will be unable to tell you that you are being struck by another radar. If this is a concern then you are advised to switch your radar into its standby mode when you are not actually using it. You probably do this anyway in order to save power. -- Best regards, John Navas http:/navasgroup.com |
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#4
posted to rec.boats.electronics
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Microwave leak detector - active radar reflectors
John Navas wrote in
: Marine radars have a limited vertical beam width, and the transponder should be mounted above or below that vertical pattern. See the Handbook: WRONG! Geez, John.... Marine radars have limited HORIZONTAL beamwidth so you can see 3 targets kinda close together as 3 targets, not 1 blob. They have WIDE VERTICAL beamwidth so they are pointing at the horizon EVEN WHEN THE BOAT IS HEELED OVER OR ROLLING! If they had narrow vertical beamwidth, the only time you'd see the target is in flat water or at the marina dock! |
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#5
posted to rec.boats.electronics
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Microwave leak detector - active radar reflectors
On Mon, 21 Jan 2008 16:48:25 +0000, larry wrote in
: John Navas wrote in : Marine radars have a limited vertical beam width, and the transponder should be mounted above or below that vertical pattern. See the Handbook: WRONG! Geez, John.... Marine radars have limited HORIZONTAL beamwidth so you can see 3 targets kinda close together as 3 targets, not 1 blob. They have WIDE VERTICAL beamwidth so they are pointing at the horizon EVEN WHEN THE BOAT IS HEELED OVER OR ROLLING! If they had narrow vertical beamwidth, the only time you'd see the target is in flat water or at the marina dock! Read the Handbook. 30° is actually greater than many units. Garmin GMR 18 HD and GMR 24 HD are 25°. Likewise Furuno and Lowrance, etc. Check the specs if you still don't believe me. Many marine radars are gimbal mounted to address the heeling issue. -- Best regards, John Navas http:/navasgroup.com |
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#6
posted to rec.boats.electronics
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Microwave leak detector - active radar reflectors
In article ,
larry wrote: John Navas wrote in : Marine radars have a limited vertical beam width, and the transponder should be mounted above or below that vertical pattern. See the Handbook: WRONG! Geez, John.... Marine radars have limited HORIZONTAL beamwidth so you can see 3 targets kinda close together as 3 targets, not 1 blob. They have WIDE VERTICAL beamwidth so they are pointing at the horizon EVEN WHEN THE BOAT IS HEELED OVER OR ROLLING! If they had narrow vertical beamwidth, the only time you'd see the target is in flat water or at the marina dock! "Limited" is such a nondescript word. It really doesn't define what either of you are trying to say. Marine Radar Antennas, typically have a 25 Degree Vertical Beamwidth, Now to some that may be "Limited", (25° as opposed to 360°) but when compared to a Marine Radars Horizontal Beamwidth, (Typically 2° to 6°) it is not "Limited" at all. John's Point, was that the Radar Transponder MUST be mounted Clearly OUTSIDE the Vertical Beamwidth of the Onboard Radar, so as to not be triggered by the operation of the onboard Radar. This is correct. Bruce in alaska -- Bruce in alaska add path after fast to reply |
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#7
posted to rec.boats.electronics
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Microwave leak detector - active radar reflectors
Bruce in alaska wrote in news:fast-EB795C.10155321012008
@netnews.worldnet.att.net: John's Point, was that the Radar Transponder MUST be mounted Clearly OUTSIDE the Vertical Beamwidth of the Onboard Radar, so as to not be triggered by the operation of the onboard Radar. This is correct Noone is going to run a radar transponder and radar on the same boat. That transponder is going to go berserk re-radiating your own radar. There's all kinds of crazy side lobes on the ****ty PC board antenna on any radome array. The lobes don't have a lot of power, but sure more than enough power to set off a transponder, even if you put the damned antenna in the BILGE! What a crazy idea.... |
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#8
posted to rec.boats.electronics
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Microwave leak detector - active radar reflectors
On Tue, 22 Jan 2008 06:19:37 +0000, larry wrote in
: Bruce in alaska wrote in news:fast-EB795C.10155321012008 : John's Point, was that the Radar Transponder MUST be mounted Clearly OUTSIDE the Vertical Beamwidth of the Onboard Radar, so as to not be triggered by the operation of the onboard Radar. This is correct Noone is going to run a radar transponder and radar on the same boat. That transponder is going to go berserk re-radiating your own radar. There's all kinds of crazy side lobes on the ****ty PC board antenna on any radome array. The lobes don't have a lot of power, but sure more than enough power to set off a transponder, even if you put the damned antenna in the BILGE! What a crazy idea.... Not at all. They serve different purposes, and are complementary. -- Best regards, John Navas http:/navasgroup.com |
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#9
posted to rec.boats.electronics
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Microwave leak detector - active radar reflectors
In article ,
larry wrote: .... Noone is going to run a radar transponder and radar on the same boat. Is it? ... but sure more than enough power to set off a transponder, even if you put the damned antenna in the BILGE! Of course, but so what. I cannot see anything with my radar up to some 15 metres anyway (assuming 50 ns pulse). The key is if it still responds to other radars. What a crazy idea.... Why? The radar expands what I see, and the transponder expands, what others with a radar see. I have seen how unreliable echos from glass fibre reinforced polyester boats are (and how unreliable echos at least smaller passive radar reflectors of the 90° aluminum sheets type give on quiet waters). Small wonder aircraft all have a transponder. Marc -- remove bye and from mercial to get valid e-mail http://www.heusser.com |
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