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Old 13-12-2015, 09:36   #106
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Re: Tired of Bugs in Navico Equipment

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Originally Posted by poiu View Post
In the Navico promotional information that they say they use a technique to improve the resolution of the radar. The 3g doesn't have the 'beam sharpening' 'target separation control' technology, but the 4g does and so improves effective beam angle from 5.2 deg to 2.6 deg. I am sure it is edge detection. Looking for a rising and falling return over the leading and falling edge of the return. How else could it be done? Also, if it is done like this, then it should be possible to obtain an even higher target resolution shouldn't it?
"Effective beam angle" is propaganda -- the beam angle is what it is; "beam sharpening" is virtual -- it's signal processing performed on the received signal. In the case of the Simrad 4G radar, the purpose is improved bearing resolution, which is different from bearing accuracy, which is what we were talking about. I can confirm that the bearing resolution and target discrimination of this radar is definitely superior to that of small pulse radars, but I don't know whether the bearing accuracy is any better, or whether bearing accuracy is in any way enhanced by Simrad's "beam sharpening", although it probably is.

It's not edge detection -- radar signal processing techniques are much more sophisticated, involving Fourier transformations and all kinds of carp which I don't understand. The point of most of these techniques seems to be to separate noise from real data -- just like in DSP techniques for audio signals.


I find Navico's hype irritating. They imply that they invented FMCW radar, that it is something brand new which has made pulse radar obsolete, and that they have achieved leaps forward in technology by whole generations. Bullocks! FMCW radar has been around almost as long as pulse radar, and it was certainly not Navico who invented various signal processing techniques. It is not really revolutionary, which is not to say that it's not good -- on the contrary, it is cheaper to make than pulse radar, has no magnetron to replace or to be warmed up, is better at close in work which is most relevant for recreational sailors, and with clever signal processing behaves much like a larger radar set. If they would just ditch their carp MARPA module and start over again (buy it from Furuno?), it would be really great.
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Old 13-12-2015, 09:55   #107
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Re: Tired of Bugs in Navico Equipment

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OK, I see what you are saying now. I was making the simplification that the garbage on either side of the echo would always be the same. You are saying that it's +/- based on the echo return becoming strong enough for the detector to trip. So the garbage on either side is only +/- equal, not exactly equal.

Wouldn't the sharpness of the edge depend primarily how rapidly the beam power drops off at the edges rather than the beam width? I've seen the "edge" specified as 3db less than the center power or something like that, but that's just a paper spec. I know nothing about beam shaping and the degree to which one can obtain sharp edge drop-off independent of beam width. You are saying they are related, which I don't doubt, but how much?

It would be interesting to know how many degrees of rotation the no-detect/detect transition takes.

What I do know is that Furuno specs bearing accuracy to 1 deg on a number of their radars, large beam and small beam. I take that to mean they can determine the bearing to target with that precision, taking all these factors into account.
This: "You are saying that it's +/- based on the echo return becoming strong enough for the detector to trip. So the garbage on either side is only +/- equal, not exactly equal." Is exactly right. If you translate the detector's "trip" threshold accuracy range into the space domain, you'll see that accuracy in the space domain will be a linear function of the steepness of the gradient of the signal strength versus momentary antenna angle -- the "sharpness" of the beam. If a beam has the same shape (and it will, given the same antenna design), then the wider the beam, the less "sharp" it will be, and the less accurate will be our detection of the "edges" of the beam, and thus of bearing to the center of the target.

Remember radio waves aren't light, and we don't have "lenses" to focus them (leaving aside phased arrays and other techniques not available to recreational sailors). The reflection from the target doesn't come back as an image such as we might capture in a camera. It comes back as increased intensity of radiation at that frequency.

Now all that being said, not all radar antennae are equal. Dome radars use parabolic torus reflectors; "open array" radars use waveguide slot antennae. The latter type has much less sidelobe radiation than the former. But for any given antenna type, the beamwidth is a function of aperture width -- so you just can't beat antenna size.

Why Furuno advertises their radars as having 1 degree bearing accuracy is clear -- IMO Performance Standards require at least 1 degree bearing accuracy. Whether the larger radars are really no better, I don't know, but if that's the case, it can only be because the smaller radars have better signal processing or better antennae, in order to overcome inherently lesser bearing accuracy.
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Old 13-12-2015, 15:45   #108
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Re: Tired of Bugs in Navico Equipment

I'm sure you meant "radio waves aren't visible light"?

I have no experience with the different type of antennas, but I know that in our Furuno dome is an antenna that is some section of a cone (probably a parabola), but that section has many tiny deep slots across it. What type is this?

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Old 14-12-2015, 04:08   #109
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Re: Tired of Bugs in Navico Equipment

Quote:
Originally Posted by Dockhead View Post
"Effective beam angle" is propaganda -- the beam angle is what it is; "beam sharpening" is virtual -- it's signal processing performed on the received signal. In the case of the Simrad 4G radar, the purpose is improved bearing resolution, which is different from bearing accuracy, which is what we were talking about. I can confirm that the bearing resolution and target discrimination of this radar is definitely superior to that of small pulse radars, but I don't know whether the bearing accuracy is any better, or whether bearing accuracy is in any way enhanced by Simrad's "beam sharpening", although it probably is.

It's not edge detection -- radar signal processing techniques are much more sophisticated, involving Fourier transformations and all kinds of carp which I don't understand. The point of most of these techniques seems to be to separate noise from real data -- just like in DSP techniques for audio signals.


I find Navico's hype irritating. They imply that they invented FMCW radar, that it is something brand new which has made pulse radar obsolete, and that they have achieved leaps forward in technology by whole generations. Bullocks! FMCW radar has been around almost as long as pulse radar, and it was certainly not Navico who invented various signal processing techniques. It is not really revolutionary, which is not to say that it's not good -- on the contrary, it is cheaper to make than pulse radar, has no magnetron to replace or to be warmed up, is better at close in work which is most relevant for recreational sailors, and with clever signal processing behaves much like a larger radar set. If they would just ditch their carp MARPA module and start over again (buy it from Furuno?), it would be really great.
I was more making the point about resolution in the sense of image resolution, resulting in improved target discrimination. This is the bottom line to which improved bearing accuracy is an element. Resolution will be a product of bearing resolution, bearing accuracy, beam width and techniques such as are used by Simrad at presumably edge detection.

I don't believe you can use this technique with a pulse radar, but not withstanding the fact that Simrad do spin more than I like also with marketing hype, it does look like they have done something pretty clever and useful there. It is hard to know what to call it. 'Effective beam angle' or 'beam sharpening' or 'the latest 4g radar' does indeed sound like marketing rowlocks.

If they only could sort out their software and bring it up to Furuno's standards, then they would have a product beyond reproach. Will it be done before next winter, when my mast comes out and I get a new radar? They might do. It sounds like they have finally fixed their software glitches on the seemingly otherwise excellent RS35 and HS35 VHF units.
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Old 14-12-2015, 08:10   #110
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Re: Tired of Bugs in Navico Equipment

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Originally Posted by colemj View Post
I'm sure you meant "radio waves aren't visible light"?
Depends on who your physics teacher was. Some of them call all EM radiation "light"; as far as I know, the majority do not, at least not back in the stone age when I was in school. Radio waves behave quite differently from light, not just visible light, but IR and UV light as well.


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I have no experience with the different type of antennas, but I know that in our Furuno dome is an antenna that is some section of a cone (probably a parabola), but that section has many tiny deep slots across it. What type is this?

Mark
That sound like a parabolic toroid antenna. The slots are to create the resonant frequency.

Slots are also used in waveguide antennae, like the "open arrays" common on larger recreational radars.
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Old 14-12-2015, 08:20   #111
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Re: Tired of Bugs in Navico Equipment

Quote:
Originally Posted by poiu View Post
I was more making the point about resolution in the sense of image resolution, resulting in improved target discrimination. This is the bottom line to which improved bearing accuracy is an element. Resolution will be a product of bearing resolution, bearing accuracy, beam width and techniques such as are used by Simrad at presumably edge detection.

I don't believe you can use this technique with a pulse radar, but not withstanding the fact that Simrad do spin more than I like also with marketing hype, it does look like they have done something pretty clever and useful there. It is hard to know what to call it. 'Effective beam angle' or 'beam sharpening' or 'the latest 4g radar' does indeed sound like marketing rowlocks.

If they only could sort out their software and bring it up to Furuno's standards, then they would have a product beyond reproach. Will it be done before next winter, when my mast comes out and I get a new radar? They might do. It sounds like they have finally fixed their software glitches on the seemingly otherwise excellent RS35 and HS35 VHF units.
Well, resolution is a different property -- it's analogous to optical resolution, and so it's the ability to resolve different targets or other detail located closer together. Here obviously beamwidth is the key characteristic. Tangled Tree had asserted that resolution and bearing accuracy are completely separate qualities, on the basis that your radar can find the center of any blip for an accurate bearing.

I think I have shown that resolution and bearing accuracy are not unrelated, but there are a few other elements to bearing accuracy which can mean that a radar with good resolution might not have as good bearing accuracy (accurate compass input being one of these). On the other hand, I do think that a radar with good bearing accuracy must have good resolution, without which you cannot determine the location edges of the blip with enough accuracy to calculate the center.
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Old 14-12-2015, 17:42   #112
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Re: Tired of Bugs in Navico Equipment

I agree with you that there is some slop in when a target will first be detected as the beam's outer reaches encounters the target, and as the beam's power ramps up enough for detection to begin.

What I don't know is how many degrees of rotation it takes for that transition to happen. Perhaps you do? It presumably relates to how quickly the beam's power drops off at the edges. Does power ramp up quickly enough for the target to register over the course of 1 deg? 2 deg? 1/10th degree? 1/100th degree? It seems to me that this will determine how accurately the beam will register the beginning and end of a target.
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Old 15-12-2015, 03:25   #113
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Re: Tired of Bugs in Navico Equipment

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Originally Posted by tanglewood View Post
I agree with you that there is some slop in when a target will first be detected as the beam's outer reaches encounters the target, and as the beam's power ramps up enough for detection to begin.

What I don't know is how many degrees of rotation it takes for that transition to happen. Perhaps you do? It presumably relates to how quickly the beam's power drops off at the edges. Does power ramp up quickly enough for the target to register over the course of 1 deg? 2 deg? 1/10th degree? 1/100th degree? It seems to me that this will determine how accurately the beam will register the beginning and end of a target.
Well it depends on the radiation pattern of the antenna and the sensitivity and gain setting of the radar set -- you can't answer it for all radars.

A directional antenna like what you use for radar attempts to concentrate the radiation energy as much as possible in one direction, but this concentration is relative -- some radiation is emitted in all directions. So it's not at all like a laser, or even like a beam of visible light. Maybe this will help you to visualize it:

Click image for larger version

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https://www.feko.info/applications/w...array/document

Those graphics of radar beams showing the shape of them are misleading, because they are showing the location of a certain contour line, and this does not illustrate at all the gradient of intensity of the radiation.

It's like a chart with a 5 meter contour line - the existence of that line doesn't say anything about the slope of the bottom.

The above graphic shows not the contour line, but the gradient at different angles expressed in dB of attenuation (or dB of normalized gain, that is, what is less than the peak gain of the antenna). Look at the "H" plane.

So you see that there isn't a really sharp drop off in signal strength with this particular antenna until you get to 15 degrees off center. And I guess that's going to be pretty typical. The type of antenna described happens to be the type which is used in open array radars.

And there's no answer to your question about how many degrees you have to rotate to get a "trip". The answer depends on the accuracy of the sensor and the slope of the signal strength gradient at the particular angle in question. As we discussed before, the wider the beam is, the shallower this gradient will be at the edges, so the greater uncertainty in the "trip" point. That translates to less accuracy.

The way to get sharper edges is with a narrower beam. That's why you won't find a radar with a high degree of bearing accuracy but low resolution (target definition).
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Old 15-12-2015, 07:29   #114
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Re: Tired of Bugs in Navico Equipment

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Originally Posted by Dockhead View Post
Depends on who your physics teacher was. Some of them call all EM radiation "light"; as far as I know, the majority do not, at least not back in the stone age when I was in school. Radio waves behave quite differently from light, not just visible light, but IR and UV light as well.
I know the term "light" is mostly used colloquially, but consider the "C" term in E=mc2.

As for radio waves behaving differently than visible light, you differ from Einstein on this, so one of you has to be wrong.

A photon is a photon and they all behave the same. If radio waves behaved differently than visible light waves, we wouldn't have radio astronomy, x-ray machines or gravitational lensing.

Or radar.

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Old 15-12-2015, 08:18   #115
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Re: Tired of Bugs in Navico Equipment

I read about this matter in different blogs now for months.
Some unsatisfied customers seems like start they own crusade or little war about show how's bad are Navico radar because a flaky ARPA/MARPA function.
As a professional engineer working for years as marine electronic design, I understand the complexity of the matter and the level of compromise every brand take at the time to design a radar.
For the common john doe, sometimes not even know that function work and mostly common people just use the radar as a safety resource but they're incapable to squeeze all information or data so all discussion is a nonsense..
I think the are more specific forums to ventilate "engineering-type" of post with formulas and diagrams about beams, power, track, etc...
I found a lot of rage with this specific product; I start to ask myself if is a problem with the product or is more a personal question?? kind of revenge..
After all.. Navico give a full refund for the faulty product...
..one of this days I gonna read about this matter on yelp....
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Old 15-12-2015, 10:19   #116
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Re: Tired of Bugs in Navico Equipment

I guess it is different perceptions. I personally have not read any "rage" into anything that has been written, and pretty much all of the bugs that have been pointed out do actually exist - all acknowledged by Navico, some fixed now, some not.

People like Tanglewood doing actual tests side by side with different radars and antennas and presenting the results cannot be considered "crusading". In fact, he should be lauded, as everyone who steps up and does similar with other equipment.

I don't see why this is not a proper forum for presenting technical details and operating theory of electronics. In fact, I think it is a perfect forum because the members here comprise a large swath of expertise in many cross-disciplines. Really, we have right here in CF CANBUS engineers, software engineers, electronics designers, people with advanced degrees in every slice of science and engineering known, and people with decades of experience using navigation equipment both commercially and recreationally. We even have the vendors for many of the products themselves on the forum.

I don't think I have come across another forum as learned and diverse as CF.

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Old 15-12-2015, 11:32   #117
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Re: Tired of Bugs in Navico Equipment

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I don't see why this is not a proper forum for presenting technical details and operating theory of electronics. In fact, I think it is a perfect forum because the members here comprise a large swath of expertise in many cross-disciplines. Really, we have right here in CF CANBUS engineers, software engineers, electronics designers, people with advanced degrees in every slice of science and engineering known, and people with decades of experience using navigation equipment both commercially and recreationally. We even have the vendors for many of the products themselves on the forum.

I don't think I have come across another forum as learned and diverse as CF.

Mark
I concur with Mark's point of view. My primary interest in following the forum is to gain better insight and understanding by reading the responses of some of the very knowledgable members of CF.
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Old 15-12-2015, 17:01   #118
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Re: Tired of Bugs in Navico Equipment

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I know the term "light" is mostly used colloquially, but consider the "C" term in E=mc2.

As for radio waves behaving differently than visible light, you differ from Einstein on this, so one of you has to be wrong.

A photon is a photon and they all behave the same. If radio waves behaved differently than visible light waves, we wouldn't have radio astronomy, x-ray machines or gravitational lensing.

Or radar.

Mark
Who am I to disagree with Mr. Einstein?

Of course I wouldn't, although I have only my old physics teacher, no doubt long dead, as a reference.

But for the practical matter at hand - we can focus light -- visible plus UV and IR if you like -- with lenses into a tight beam with sharp edges. Or even arrange for it to be emitted as a coherent laser beam. Radio waves in the microwave range cannot be focused with a lens (in the same way as light, or in any way available to us so far). There is of course such a thing as a MASER, but this is far, far beyond anything available to us. Therefore, our radars have to interpret the reflections from a blurred, incoherent beam of radiation -- the whole point of this part of the discussion.

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Old 15-12-2015, 17:07   #119
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Re: Tired of Bugs in Navico Equipment

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Originally Posted by colemj View Post
I guess it is different perceptions. I personally have not read any "rage" into anything that has been written, and pretty much all of the bugs that have been pointed out do actually exist - all acknowledged by Navico, some fixed now, some not.

People like Tanglewood doing actual tests side by side with different radars and antennas and presenting the results cannot be considered "crusading". In fact, he should be lauded, as everyone who steps up and does similar with other equipment.

I don't see why this is not a proper forum for presenting technical details and operating theory of electronics. In fact, I think it is a perfect forum because the members here comprise a large swath of expertise in many cross-disciplines. Really, we have right here in CF CANBUS engineers, software engineers, electronics designers, people with advanced degrees in every slice of science and engineering known, and people with decades of experience using navigation equipment both commercially and recreationally. We even have the vendors for many of the products themselves on the forum.

I don't think I have come across another forum as learned and diverse as CF.

Mark
I agree with every word of this post. Well said.

I've learned as much on this forum, on an amazingly broad spectrum of subjects, from an amazing variety of knowledgeable people, as I probably learned at university. Sometimes the digressions are the best parts of these threads.

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Old 16-12-2015, 08:52   #120
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Re: Tired of Bugs in Navico Equipment

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But for the practical matter at hand - we can focus light -- visible plus UV and IR if you like -- with lenses into a tight beam with sharp edges. Or even arrange for it to be emitted as a coherent laser beam. Radio waves in the microwave range cannot be focused with a lens (in the same way as light, or in any way available to us so far). There is of course such a thing as a MASER, but this is far, far beyond anything available to us. Therefore, our radars have to interpret the reflections from a blurred, incoherent beam of radiation -- the whole point of this part of the discussion.
Sorry, absolutely everything one can do to visible light can be done with any other frequency of EM. Lensing in all forms, forming coherent beams, etc. It is the basic physics behind photons. Microwaves, in particular, have well-advanced lensing, since they are our main communication and probe frequencies.

And the lower the frequency, the more "blurred" the edges are (just try to focus radio frequencies without them diffracting and interacting all around the beam edge). Visible light by no means forms tight beams with sharp edges. Microwaves are much better in this regard.

Radar made of visible light (LIDAR, which is in wide use - think radar guns and range finders, for example) has less resolution than our current microwave sets - and they use lasers for the light source.

One reason visible light (LIDAR) isn't used for navigational radar is because it is so poor in this application (and is opaque to dust, rain, etc).

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