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Old 08-29-2018, 07:13 AM   #21
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The radar displayed on the left is obviously not tuned or given sufficient gain to show the targets properly. Please keep us informed of your findings.
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Old 08-29-2018, 07:19 AM   #22
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Assuming that I am not moving. If I'm moving, then we're only looking at RELATIVE motion.

Of course. Mine was an attempt to provide a simplified example of Doppler.
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Old 08-29-2018, 07:30 AM   #23
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As to the generalization of doppler radar and NOT Marine doppler specific with bells and whistles...

From Wikipedia....

"A*Doppler radar*is a specialized*radar*that uses the*Doppler effect*to produce velocity data about objects at a distance. It does this by bouncing a*microwave*signal off a desired target and analyzing how the object's motion has altered the frequency of the returned signal. This variation gives direct and highly accurate measurements of the*radialcomponent of a target's velocity relative to the radar. Doppler radars are used in*aviation, sounding satellites,*Major League Baseball's*StatCast system,*meteorology,*radar guns,[1]*radiology*and*healthcare*(fall detection[2]*and risk assessment, nursing or clinic purpose[3]), and*bistatic radar*(surface-to-air missiles).

Partly because of its common use by television meteorologists in on-air weather reporting, the specific term "Doppler Radar" has erroneously become popularly synonymous with the type of radar used in meteorology. Most modern*weather radars*use the*pulse-Doppler*technique to examine the motion of*precipitation, but it is only a part of the processing of their data. So, while these radars use a highly specialized form of*Doppler radar, the term is much broader in its meaning and its applications."
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Old 08-29-2018, 08:11 AM   #24
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The digital radars have been around for a long time, probably came along somewhere in the 70s or so. The previous analog radars were pretty crude, only black and white but some guys like them because you could fine tune them if you knew what you were doing.

Digital radars gave us color and just a lot easier to interpret displays.

My experience is in aviation radars which is a tad different that marine radar but the basics are the same. Aviation radars are basically designed to see weather and avoid thunderstorms. I've used all of the above types and the latest and greatest is quite nice, but I'm not overly excited about the benefits of doppler. Doppler in aviation is designed to see water partial movements to determine turbulence.

In marine, the doppler is suppose to notice motion better so you can spot moving boats. That doesn't seem like a huge deal to me. The goal is to see ANY object out there, boat, marker or rock and avoid it. If you see anything, there's a pretty good chance you'll cause some damage if you hit it. Seems like one advantage of doppler is it could tell you the difference between a moving boat and a large rock.

Now, the solid state or pulsed radar is the latest development before the doppler trend and that seems like a pretty big step. No more magnetron. In comparing my Simrad 4G pulsed radar with my previous experience using an older digital Raymarine is a big step. And I've got the cheaper 4G unit. I can tweak it to show crab traps if not too choppy. However, still learning with it.

As for marine radar, it's best function is to avoid an object, and does reasonably well at that. Some folks use it for weather avoidance, but I could argue it has a lot of shortcomings for that. And ya really can't outrun the weather in a boat anyway.
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Old 08-29-2018, 08:40 AM   #25
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Not much to add as most of the above is correct.
Let me add my two cents.

Doppler radar was the first radar that could identify rotational motion in clouds. For the first time, radar could spot tornadoes and rotational motion in thunderstorms in which tornadoes were born. It was a big step in severe weather forecasting.
Weather radars also have longer wavelengths then other mobile based radars because they are designed to punch thru precipitation.
But that makes them less effective in seeing clouds.
TV stations jumped on the bandwagon because they had more money then common sense.
It's promotion in the boat market now, is in the same vein. Technology for those who can pay for it. What it can tell them is another story.

I'm not up on the new broadband radars.

I hated my Raymarine E80 radar the first year until I realized that none of the automatic settings really work. Once I started to adjust the gain and filter for the sea conditions, it's amazing the stories I can get that radar to tell me. I will not replace it.

Because all radars are limited by physics. Digital radar is like CDs versus vinyl records. It may sound better, but it just masks what its algorithms think you don't need to know.

The most important thing to keep in mind is that it may show you the big tanker in front of you, but it's not telling you what's behind that tanker.
In the same vein, if your radar it's showing you a big rain shower, it's not telling you what's behind. Nothing doesn't necessarily mean nothing.
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Old 08-29-2018, 08:45 AM   #26
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Raytheon Company, the company that made the magnetron affordable from those developed in England just prior to WWll, gave up all manufacturing of microwave power magnetrons, amplitrons and TWTs some 25 years ago. They sold the entire division.

Since then solid state has began replacing the old maggies which I think will see very limited future applications such as in ovens.
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Old 08-29-2018, 09:11 AM   #27
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I just read a little bit about broadband radar. Looks interesting, bit I'd like to know how much the frequency really varies.

The pulsed radars seem marketed to those who think long range is better. My long range is 6 nm. 12 if I get really wild. If you tune your radar for long range stuff that can't hurt you, you'll miss the stuff that can.

The Garmin ad for their pulsed, Doppler radar seems targeted to the drug runner market, "...detect and highlight moving targets, such as small, fast vessels headed your way..." Like patrol boats. Opps, my addition.
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Old 08-29-2018, 10:15 AM   #28
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My interpretation of doppler effect usage is different than what you guys have mentioned. It's not about birds or rain. It's basically like a Furuno ARPA implementation. The radar acquires targets then tracks them, developing a course and speed. Comparing that to our own boat, it colors "safe targets" green and "dangerous targets" red. The MFD does this but only for AIS targets.

My thought especially for guests on board helping out, this is an added safety advantage/convenience.

I haven't done a lot with it besides view the red/green. I need to see what else I can do with it, see if it shows CPA, TCPA and so on.
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Old 08-29-2018, 03:10 PM   #29
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Yes I understand that many who fish seek out flying birds as an indicator where there could be fish. My ONLY need for radar is for collision avoidance so the radar that can reach out beyond about 5 miles provides no attraction to me.

A solid state radar does not require an ATR device (anti transmit/receive) that resides inside the waveguide. Itís purpose is to prevent the receiver which shares the same waveguide as the transmitter from kissing goodbye when the transmitter transmits a pulse of high power energy.

These devices have recovery time which affects the minimum range....could be 1/8-1/4 mile or so. A solid state unit can see targets a few feet from where the antenna is mounted. One needs to check the particular radarís specifications for actual numbers.
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Old 08-29-2018, 03:37 PM   #30
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I am not good at adjusting radar. Therefore I try to mess with it as little as possible. I just want to know about any fast boat out there in the fog that I need to be aware of so I can avoid them.
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Old 08-29-2018, 04:00 PM   #31
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Doppler helps with motion detection, but is only an aid. The most capable motion detection is ARPA which will show you the course and speed of another vessel. It does it by tracking successive positions of the target over time, and calculates the direction and speed of travel.


Doppler is another tool to help, providing a much faster way to measure the approaching speed of a target. Rather than needed to track a bunch of positions over time to assess speed, doppler can measure it in a single sweep. That's really useful, but it only measured the closing speed, i.e. how fast the target is getting closer to you. If the target is moving, but not in a way that is getting closer, doppler won't know it's moving, and you have to revert back to tracking successive positions. So dopper is an aid to target tracking, but not a replacement for ARPA-style tracking. But collision risks are from boats that are getting closer, so Doppler quickly identifies the ones you case about most, and that is really good.


It's also worth noting that there are other ways to quickly identify trouble targets. Furuno's fast tracking (or whatever they call it) basically tracks all targets all the time. Then, when you say you want to "acquire" a target, it starts displaying right away because it's been getting tracked all along. It's pretty cool, and a good way to make use of lots of processing power in current computers.


As for needed to know the boat's current speed and direction, that's actually vital to all of these tracking technologies. Doppler measures the closing speed between you and a target. But to figure out the speed over ground of the target you need to subtract out your own speed and direction using vector math. ARPA won't even work without speed and heading inputs.
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Old 08-29-2018, 05:06 PM   #32
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Ultimately, those good with radar only need the basic function of radar....target distance and direction.

Targets closing in on the center of the screen are potential collisions, those tracking elsewhere...are not.

All other functions help make some of your navigation decisions faster or more accurate which is good.
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Old 08-30-2018, 07:23 AM   #33
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Per another thread, pick up a copy of The Radar Book if you don't know how to use yours; in tandem with the operating manual for your model, you will discover the wide number of uses for this tool.

Quote:
Some folks use it for weather avoidance, but I could argue it has a lot of shortcomings for that. And ya really can't outrun the weather in a boat anyway.
I really disagree with this, having used radar to both avoid storms and to prepare for them. In a slow boat you avoid storms b.y getting out of their path. Storm tracking is why I like to have a longer range open array radar, mounted as high as possible. I am curious what those "lot of shortcomings" are. It is superior to weather radar obtained on the internet, because it shows the storm relative to your specific position. Used in combination with internet or better yet satellite weather, it is a very powerful weather tool
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Old 08-30-2018, 08:02 AM   #34
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Sure you can't out run weather sometimes, but if you are out of internet/cell range and you don't have satellite weather...radar at least gives you the info for an informed decision.

You may not be able to out running it, but you may be able to pick your way though the weaker storms.
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Old 08-30-2018, 07:01 PM   #35
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Being able to pick a path between ts cells in real time is useful but then so is seeing no path. Internet radar is 5 or 10 minute snapshots. Better than nothing.
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Old 09-02-2018, 03:32 PM   #36
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... The one radar innovation which I really like is the phased-array antennas, whichare swept electronically without actually rotating.
...
The problem with phased array radars is that they have limited sweep angles.
For aircraft that are more concerned with what is in front of them, this type of radar can work. To cover 360 deg like most boat radars would require multiple arrays and a fused display system. Aegis cruisers have large phased array radars, but they require an antenna for each quadrant around the ship.

It is unlikely to be practical for a smallish boat at a reasonable cost for not a lot of added benefits.
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Old 09-03-2018, 01:32 PM   #37
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Loved my 40yr old Furuno magnetron,CRT with the gain, tune, ftc, stc and range with individual knobs.
Great for entering a strange harbour in high winds, rain and in the dark. Could manipulate each without ever menus trying to quickly find the appropriate items.

I have a newer Garmin HD and it's ok but when you need it and you need it fast the auto settings are inadequate and 10 seconds in a strange dark harbour mouth is a long time.

However, finding the newer Garmin controls
is breeze compared to the much buried menus in Raymarine equipment.

I have a beef with all the manufacturers pushing the auto features and suggesting that anyone can be proficient with these machines after reading their manuals. 25yrs ago it took me an eleven week course to get Radar/ARPA/MARPA certified and another year of almost daily use to get good at it..
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Old 09-03-2018, 02:07 PM   #38
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For what it's worth, as I have nothing to compare to; crossing Albemarle Sound I noted a target 3 mi off our port beam. First mate was tasked with IDing it as it was paralleling us. This is a woman who can spot a crab pot at a half mile with the naked eye.
Target now steering an intercept, still no ID. Target now one mile out on collision course. No ID. We slowed not sure what was going on. Mid day, no wave chop. As the target crossed in front we had to laff. Three pelicans.
Our Garmin HDx seems quite capable, has even picked up boats on the back of thunder cells.
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Old 09-03-2018, 02:17 PM   #39
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BUT, how does doppler work when the radar itself is moving at about the same rate as the rain target, for instance? Does the radar know the boat speed and direction and subtract that from the relative target speed?
Microwaves move at the speed of light. Pretty sure rain targets are moving slower than that. (I'm ignoring the pokey processing speed of the electronics)
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Old 09-03-2018, 02:36 PM   #40
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For what it's worth, as I have nothing to compare to; crossing Albemarle Sound I noted a target 3 mi off our port beam. First mate was tasked with IDing it as it was paralleling us. This is a woman who can spot a crab pot at a half mile with the naked eye.
Target now steering an intercept, still no ID. Target now one mile out on collision course. No ID. We slowed not sure what was going on. Mid day, no wave chop. As the target crossed in front we had to laff. Three pelicans.
Our Garmin HDx seems quite capable, has even picked up boats on the back of thunder cells.
Yup, but throw in some weather and you can lose a 50 footer if you can't adjust fast enough.
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