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#71
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Radar vs GPS/Sounder
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#73
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Radar vs GPS/Sounder
An interesting explanation, but this isn't the image I see. They appear from
medium sized vessels (tugs, CG, etc). They are roughly a 90 degree arc of a circle centered on my vessel, and intersecting the target. Thus, the radius indicates range, and the position of the arc is the approximate direction. Although I always assumed it was something "active" on the target, I'm beginning to think it might be entirely my radar. The fact that the arc is on both sides of the target makes me think that my transmitter is radiating small side lobes (if that's the correct term) that precede and follow the main beam. If the target is a large reflector, and my gain is high, that might show as the arc. -jeff "Me" wrote in message ... In article , wrote: On Mon, 01 Dec 2003 19:17:04 GMT, Me wrote: Again bull****! Would be nice if you knew anything about what your talking about. That's why, my little trollsmeg, I said "my understanding". Perhaps you would enjoy taking the lid off that planet-sized intellect to share your god-like insights with this NG? Or just shut the **** up. R. There isn't a "Commercial Radar" marketed in the USA that has anywhere near enough Beam Energy Density to cook even your eyeballs, let alone any other body parts of any mammal, while in operation, in a standard installation. One is very much more likely to be hurt by the antenna hitting them in the head, as it rotates than by the RF coming out of the antenna. This has been well documented over the last 30 years, and as the power of these radars has dropped due to the better receiver technology, it is more true now than 30 years ago. Next, The dashed arc's one sees displayed on radar screens are other radars that have transmitting frequencies CLOSE to the receive frequency of your radar. There is a wide range of frequencies that Xband radars can and do use and the reciver bandwidth is much narrower than the transmitter frequency range by 20X or so. Transmit frequencies are determined by the physical properties of the Magnitron of each radar and are fixed at the MFG, but do move around due to temp, age, ect. This means that some show up on your screen and some don't. There are three different bands that Maritime Radars use Sband, Xband, and KaBand. Of the three Xband is by far the most cxommon. (Orders of Magnitude more) Sband is only found on VERY BIG VESSELS, and Kaband is used mainly for Wx search and is extremly rare aboard any vessels except Research Vessels. None of the radars will cause interference except in their own Band Class. The Arc's always show from the center of your display, and don't have any range or direction information associated with them, other than they TEND to not be there when you antenna isn't pointed toward the other radar. Targets that have Dashes the trail the target on your display are a differet thing altogether. They are Active Radar Transponders, (Racon's) and are used as Position Identification devices. These are put on significant Navigation Points and are also used for SAR Activites and ARE required on Lifeboats of SOLAS Required Ships. Almost all of these a Xband devices. I have seen one or two Sband installations, but never any Kaband. Now that your understanding has been expanded, ...... well ok...we'll just let it go at that........ me |
#74
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Radar vs GPS/Sounder
Rodney Myrvaagnes wrote:
Or, to put it differently, what ELSE is radar good for? Can I use it to determine if a freighter 10 miles away is on a collision course with me? Do others normally run with radar on, even if it's clear? Why? That is actually a different question, because a radar has value for measurement even when you can see. Example 1: If you need to anchor in a confined space, and the obstructions all show on the radar, you can maximize your scope by finding the center of a range circle that just kisses the three nearest obstructions. 2) Your chart shows you the safe distance from a headland. You put a circle of that radius on the screen. and steer so it doesn't intersect. 3) When you see a ship, you can put a bearing line on it and a range circle. If the ship comes inside the circle without moving off the bearing line you need to take action. In general, you will find that an accurate plan view of the surroundings is a valuable supplement to eyeballs. |
#75
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Radar vs GPS/Sounder
Rodney Myrvaagnes wrote:
Or, to put it differently, what ELSE is radar good for? Can I use it to determine if a freighter 10 miles away is on a collision course with me? Do others normally run with radar on, even if it's clear? Why? That is actually a different question, because a radar has value for measurement even when you can see. Example 1: If you need to anchor in a confined space, and the obstructions all show on the radar, you can maximize your scope by finding the center of a range circle that just kisses the three nearest obstructions. 2) Your chart shows you the safe distance from a headland. You put a circle of that radius on the screen. and steer so it doesn't intersect. 3) When you see a ship, you can put a bearing line on it and a range circle. If the ship comes inside the circle without moving off the bearing line you need to take action. In general, you will find that an accurate plan view of the surroundings is a valuable supplement to eyeballs. |
#76
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Radar vs GPS/Sounder
On Tue, 02 Dec 2003 19:18:13 GMT, Me wrote:
Next, The dashed arc's one sees displayed on radar screens are other radars that have transmitting frequencies CLOSE to the receive frequency of your radar. There is a wide range of frequencies that Xband radars can and do use and the reciver bandwidth is much narrower than the transmitter frequency range by 20X or so. Transmit frequencies are determined by the physical properties of the Magnitron of each radar and are fixed at the MFG, but do move around due to temp, age, ect. This means that some show up on your screen and some don't. There are three different bands that Maritime Radars use Sband, Xband, and KaBand. Of the three Xband is by far the most cxommon. (Orders of Magnitude more) Sband is only found on VERY BIG VESSELS, and Kaband is used mainly for Wx search and is extremly rare aboard any vessels except Research Vessels. None of the radars will cause interference except in their own Band Class. The Arc's always show from the center of your display, and don't have any range or direction information associated with them, other than they TEND to not be there when you antenna isn't pointed toward the other radar. Targets that have Dashes the trail the target on your display are a differet thing altogether. They are Active Radar Transponders, (Racon's) and are used as Position Identification devices. These are put on significant Navigation Points and are also used for SAR Activites and ARE required on Lifeboats of SOLAS Required Ships. Almost all of these a Xband devices. I have seen one or two Sband installations, but never any Kaband. Good summary, thanks. One might just add that the lifeboat equipment is called SARTs , Search And Rescue Transponder. Echoes 9 dots if I remember correctly. Luckily never seen one. /Marcus -- Marcus AAkesson Gothenburg Callsigns: SM6XFN & SB4779 Sweden Keep the world clean - no HTML in news or mail ! |
#77
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Radar vs GPS/Sounder
On Tue, 02 Dec 2003 19:18:13 GMT, Me wrote:
Next, The dashed arc's one sees displayed on radar screens are other radars that have transmitting frequencies CLOSE to the receive frequency of your radar. There is a wide range of frequencies that Xband radars can and do use and the reciver bandwidth is much narrower than the transmitter frequency range by 20X or so. Transmit frequencies are determined by the physical properties of the Magnitron of each radar and are fixed at the MFG, but do move around due to temp, age, ect. This means that some show up on your screen and some don't. There are three different bands that Maritime Radars use Sband, Xband, and KaBand. Of the three Xband is by far the most cxommon. (Orders of Magnitude more) Sband is only found on VERY BIG VESSELS, and Kaband is used mainly for Wx search and is extremly rare aboard any vessels except Research Vessels. None of the radars will cause interference except in their own Band Class. The Arc's always show from the center of your display, and don't have any range or direction information associated with them, other than they TEND to not be there when you antenna isn't pointed toward the other radar. Targets that have Dashes the trail the target on your display are a differet thing altogether. They are Active Radar Transponders, (Racon's) and are used as Position Identification devices. These are put on significant Navigation Points and are also used for SAR Activites and ARE required on Lifeboats of SOLAS Required Ships. Almost all of these a Xband devices. I have seen one or two Sband installations, but never any Kaband. Good summary, thanks. One might just add that the lifeboat equipment is called SARTs , Search And Rescue Transponder. Echoes 9 dots if I remember correctly. Luckily never seen one. /Marcus -- Marcus AAkesson Gothenburg Callsigns: SM6XFN & SB4779 Sweden Keep the world clean - no HTML in news or mail ! |
#78
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Radar vs GPS/Sounder
I'm going to assume you start your radar and adjust it at either 3 or
6 mile range, and when you see these arced targets, they are generally larger, at relatively close range, or when you are on a lower range. If so, first step, try increasing sea and/or rain clutter. If this doesn't get rid of them, retune the set for lower ranges (that you may be on) and reduce gain and/or intensity .... slightly. As always, try to stay on the higher ranges ... Id only use 0.75 down, for docking or running inside a marina (personal experience/choice), for example, Oak Bluffs, Hyannis inner harbor, Boston Harbor marina. otn Jeff Morris wrote: An interesting explanation, but this isn't the image I see. They appear from medium sized vessels (tugs, CG, etc). They are roughly a 90 degree arc of a circle centered on my vessel, and intersecting the target. Thus, the radius indicates range, and the position of the arc is the approximate direction. Although I always assumed it was something "active" on the target, I'm beginning to think it might be entirely my radar. The fact that the arc is on both sides of the target makes me think that my transmitter is radiating small side lobes (if that's the correct term) that precede and follow the main beam. If the target is a large reflector, and my gain is high, that might show as the arc. -jeff |
#79
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Radar vs GPS/Sounder
I'm going to assume you start your radar and adjust it at either 3 or
6 mile range, and when you see these arced targets, they are generally larger, at relatively close range, or when you are on a lower range. If so, first step, try increasing sea and/or rain clutter. If this doesn't get rid of them, retune the set for lower ranges (that you may be on) and reduce gain and/or intensity .... slightly. As always, try to stay on the higher ranges ... Id only use 0.75 down, for docking or running inside a marina (personal experience/choice), for example, Oak Bluffs, Hyannis inner harbor, Boston Harbor marina. otn Jeff Morris wrote: An interesting explanation, but this isn't the image I see. They appear from medium sized vessels (tugs, CG, etc). They are roughly a 90 degree arc of a circle centered on my vessel, and intersecting the target. Thus, the radius indicates range, and the position of the arc is the approximate direction. Although I always assumed it was something "active" on the target, I'm beginning to think it might be entirely my radar. The fact that the arc is on both sides of the target makes me think that my transmitter is radiating small side lobes (if that's the correct term) that precede and follow the main beam. If the target is a large reflector, and my gain is high, that might show as the arc. -jeff |
#80
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Radar vs GPS/Sounder
In this ill-tempered thread, Jeff's proposal is at least plausible.
Dishes have significant side lobes peaking nearer 90 degrees to the side though.... Flat plate antennas do much better with smaller side-lobes. Regular dishes sometimes get edges turned backwards to cut the side lobes. Brian W On Tue, 2 Dec 2003 16:59:39 -0500, "Jeff Morris" wrote: An interesting explanation, but this isn't the image I see. They appear from medium sized vessels (tugs, CG, etc). They are roughly a 90 degree arc of a circle centered on my vessel, and intersecting the target. Thus, the radius indicates range, and the position of the arc is the approximate direction. Although I always assumed it was something "active" on the target, I'm beginning to think it might be entirely my radar. The fact that the arc is on both sides of the target makes me think that my transmitter is radiating small side lobes (if that's the correct term) that precede and follow the main beam. If the target is a large reflector, and my gain is high, that might show as the arc. -jeff "Me" wrote in message ... In article , wrote: On Mon, 01 Dec 2003 19:17:04 GMT, Me wrote: Again bull****! Would be nice if you knew anything about what your talking about. That's why, my little trollsmeg, I said "my understanding". Perhaps you would enjoy taking the lid off that planet-sized intellect to share your god-like insights with this NG? Or just shut the **** up. R. There isn't a "Commercial Radar" marketed in the USA that has anywhere near enough Beam Energy Density to cook even your eyeballs, let alone any other body parts of any mammal, while in operation, in a standard installation. One is very much more likely to be hurt by the antenna hitting them in the head, as it rotates than by the RF coming out of the antenna. This has been well documented over the last 30 years, and as the power of these radars has dropped due to the better receiver technology, it is more true now than 30 years ago. Next, The dashed arc's one sees displayed on radar screens are other radars that have transmitting frequencies CLOSE to the receive frequency of your radar. There is a wide range of frequencies that Xband radars can and do use and the reciver bandwidth is much narrower than the transmitter frequency range by 20X or so. Transmit frequencies are determined by the physical properties of the Magnitron of each radar and are fixed at the MFG, but do move around due to temp, age, ect. This means that some show up on your screen and some don't. There are three different bands that Maritime Radars use Sband, Xband, and KaBand. Of the three Xband is by far the most cxommon. (Orders of Magnitude more) Sband is only found on VERY BIG VESSELS, and Kaband is used mainly for Wx search and is extremly rare aboard any vessels except Research Vessels. None of the radars will cause interference except in their own Band Class. The Arc's always show from the center of your display, and don't have any range or direction information associated with them, other than they TEND to not be there when you antenna isn't pointed toward the other radar. Targets that have Dashes the trail the target on your display are a differet thing altogether. They are Active Radar Transponders, (Racon's) and are used as Position Identification devices. These are put on significant Navigation Points and are also used for SAR Activites and ARE required on Lifeboats of SOLAS Required Ships. Almost all of these a Xband devices. I have seen one or two Sband installations, but never any Kaband. Now that your understanding has been expanded, ...... well ok...we'll just let it go at that........ me |
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