Interesting radar comparison, magnetron vs doppler

On Mahalo I have two Garmin radars, a GMR626 XHD2 traditional magnetron radar, and a new Fantom 24 digital radar.

I was tooling along in the Strait of Georgia last week, in intense forest fire smoke. The sky and water were just shades of gray.

I generally just show one radar, typically the Fantom, because the images are a bit more crisp than the other.

I came across what appears to be hundreds of small fishing boats, yet there are just a few blips on the radar. I range out and back in, almost nothing shows?

I fire up the 626 and there are the targets. See the picture for yourself. One thing I didn't think to review is the gain setting on the Fantom. It's probably just at the factory default.

In the second picture you can see what it looked like outside.

I did a little googling and the fire community is excited about doppler radar because it identifies smoke well. Leaves me to wonder if it can see through the smoke or not?

The HYG service guy is going to inquire with Garmin...

JustBob said:

On Mahalo I have two Garmin radars, a GMR626 XHD2 traditional magnetron radar, and a new Fantom 24 digital radar.

I was tooling along in the Strait of Georgia last week, in intense forest fire smoke. The sky and water were just shades of gray.

I generally just show one radar, typically the Fantom, because the images are a bit more crisp than the other.

I came across what appears to be hundreds of small fishing boats, yet there are just a few blips on the radar. I range out and back in, almost nothing shows?

I fire up the 626 and there are the targets. See the picture for yourself. One thing I didn't think to review is the gain setting on the Fantom. It's probably just at the factory default.

In the second picture you can see what it looked like outside.

I did a little googling and the fire community is excited about doppler radar because it identifies smoke well. Leaves me to wonder if it can see through the smoke or not?

The HYG service guy is going to inquire with Garmin...

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Well, to begin with, it is unlikely that your Fantom is doppler radar, which is used for mapping tiny particles such as individual raindrops and would, as you suspect, cover any targets you are interested in.

Without knowing the gain on either transmitter, no comparison is possible, but digital displays are popular precisely because the signal processing rejects all that annoying "clutter"...just as you discovered.

Seems like running both units and continually comparing performance seems like a good solution.

In my first career, as an air traffic controller, my employer transitioned from analog to digitized radar, but I never really liked it, still prefer "real" radar, which is what I have on Seeadler, and used with confidence as recently as yesterday in 1/4 mile vis. BTW, I always use the manual "gain" and frequently tweak it; can't imagine why one would not.

AlaskaProf said:

Well, to begin with, it is unlikely that your Fantom is doppler radar, which is used for mapping tiny particles such as individual raindrops and would, as you suspect, cover any targets you are interested in.

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Ah, my mistake. Here's what is on Garmin's product page:

MotionScope™ technology uses the Doppler effect to detect and highlight targets moving toward you or away in different colors to help avoid collisions, find flocks of birds, and track weather.

Furuno is advertising their radar as having doppler technology....whatever marketing ploy that is....

From their website...

"The*NXT*step with doppler Radar technology

The Furuno*NXT*Radar*is the next step in Radar evolution; a Solid-State Radar with pulse compression, Target Analyzer™ and Fast Target Tracking™ utilizing Doppler technology. Combined with FURUNO exclusive RezBoost™ technology for beam sharpening, NXT packs the performance of a larger Radar in a more compact package."

I will comment because the thread topic changed to what I have, and I like facts. PS, how many hours do you have with this radar? Did my third, 10 hr. overnight run last night with the new to me Furono NXT with Doppler. I have Had a traditional magnetron Ray, and a solid state Simrad prior, so I do have something to compare it to. Absolutely love it, and it does what it says it does...very well.

I have zero time with the "newgen radars".

I am not commenting on radar performance just how sometimes companies use words like "Doppler technology" and the only tech used is the paint on the array.

I have no idea whether it is true doppler or not, just putting up a lead if anyone wants to believe doppler tech is in a small boat operators grasp or not.

On 3 miles you would think the Fantom would be painting targets better than that. It must be a fault with the settings even though you're comparing a 6' 6kW open array antenna to a much smaller 2' enclosed dome antenna where the 6' is going to have a far greater advantage. I'm assuming the antennas are both parallel to the horizon and both close to the same height.
I've had sales people at dealer meetings insist that their broadband radars will pick up targets like birds just fine but they'll never convince me. There's currently nothing better for long range target detection that good old raw microwave power.

I still have an old Furuno magnetron radar that I keep putting off replacing. And no, I have not studied the newer stuff.

For my application though, I plan to move away from pulsed systems to a new CW low power unit maybe next year. Hard to chuck something that works. But back to the newer CW stuff. It should be a cake walk for manufacturers to add doppler to a CW system. Digital hardware today is very inexpensive once the software is complete.

One thing to remember, higher frequencies used with old maggies are in the X band with wavelengths of only a few centimeters. Great for clear weather but not so great when it rains and for most, a radar is most valuable at night, in the fog, rain and just sucky weather. But the short wavelengths of X band are absorbed by the water droplets that compromise the system. KU band is worse for water absorbing signals.

It's hard to come to any conclusion without equal hand tuning on each radar. But in my experience there is no comparison between a pulse (conventional) radar and a "broadband" or other continuous wave radar. The pulse radar wins, hands down.

JustBob said:

Ah, my mistake. Here's what is on Garmin's product page:

MotionScope™ technology uses the Doppler effect to detect and highlight...

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No error, if that's what it says, I believe that's what you bought, but im not sure I see the utility of it. How much bird finding and weather tracking do you do?

I make no claim to engineering expertise, but I regard myself as a sophisticated user. The one radar innovation which I really like is the phased-array antennas, whichare swept electronically without actually rotating.

'prof in Lagoon Cove BC

AlaskaProf said:

The one radar innovation which I really like is the phased-array antennas, whichare swept electronically without actually rotating.

'prof in Lagoon Cove BC

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For small boats???

foggysail said:

For small boats???

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Don't know. Certainly feasible.

I wish I knew more about the new radar. 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?

diver dave said:

I wish I knew more about the new radar. 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?

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Doppler senses the frequency shift caused by motion of the individual rain drop...many many rain drops, most of which are not moving at the "blind speed".

I'm not so good with radar, so take my experience for what it is worth (not much). But I recently switched from an old conventional raymarine 24" dome to a Garmin GMR digital 18". I also updated MFD's etc.


I wasn't real happy with the new radar at first, it wasn't finding targets like I thought it should, though it was much better than my old radar with stuff that is close to the boat, and the colors sure are pretty.


It really kind of burned me when we were crossing the stream on a clear day and it wasn't picking up a cargo ship 8 miles away that I could see clearly with the naked eye.


Eventually though I started messing with the gain and other settings and it got way better. It does a good job showing rain squalls, which is the main thing I use radar for.


Picking up birds, like for tuna fishing? Not my set. Maybe a bigger more powerful dome.

AlaskaProf said:

Doppler senses the frequency shift caused by motion of the individual rain drop...many many rain drops, most of which are not moving at the "blind speed".

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The frequency referred to by Prof above is in the returned echo. The faster the target closes, the higher the returned echo frequency. The reverse is true for targets moving away. The faster moving away, the lower the returned echo frequency. And if echo returns at the same frequency as transmitted indicates target is stationary.

A good example of doppler is to listen to a train’s whistle as the train approaches and then passes by

Doppler radar just means that the unit can detect a (very slight) change in echo frequency compared to transmit frequency due to relative motion between target and ship. It means nothing else. The "Doppler shift" thingy. It can calc relative speeds, that's it. Has nothing to do with target resolution. That could be better, or worse.

foggysail said:

...And if echo returns at the same frequency as transmitted indicates target is stationary....

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Assuming that I am not moving. If I'm moving, then we're only looking at RELATIVE motion.

As was stated above, knowing our own course and speed, the unit could do computational vector analysis to give the target's course and speed.

AlaskaProf said:

Don't know. Certainly feasible.

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Garmin, for one builds such units for aircraft, pulsed weather radar.

Sabre602 said:

Assuming that I am not moving. If I'm moving, then we're only looking at RELATIVE motion.



As was stated above, knowing our own course and speed, the unit could do computational vector analysis to give the target's course and speed.

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I believe Doppler measures the frequency shift relative to the signal itself. I could be wrong, but that is my understanding. Thus your relative speed is essentially meaningless in comparison. The Doppler shift is simply measuring the delta shift and calculating a resultant velocity. This is opposed to “regular” radar where distance is calculated based on the reflected return time of the signal as compared to when it was sent and no measurement of the frequency shift is measured. Though as you note, if you know course and speed, you could calc a relative velocity.

At least, this is what I think I understand.

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.

Sabre602 said:

Assuming that I am not moving. If I'm moving, then we're only looking at RELATIVE motion.

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Of course. Mine was an attempt to provide a simplified example of Doppler.

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."

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.

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.

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.

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.

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.

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. It’s 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 radar’s specifications for actual numbers.

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.