Broadband Radar

[AlanM]

Just returned from the London Boat Show where I was looking for a Chartplotter / Radar for our Maxi 1000. I am now thoroughly confused......... Broadband / HD / 3G / 4G ..... I have a sneeking suspicion that High Definition radar is in a relatively early phase of product development and the various manufacturers have their own products doing largely the same thing but with different technologies. Does anyone have any views as to the relative merits of Simrad Broadband vs Garmin HD vs Raymarine HD?

Grateful for useful links or input.

Thanks

 

[ChrisE]

I have the Simrad HD on my fishing boat and am well pleased with it.

Zero start up time and clear traces of small objects right down to mooring buoys. I have no experience of the other makes but am extremely pleased with it.

Oops, when I said HD I meant Broadband.....

 

[jerrytug]

FM radar, AKA broadband, can't see RACONs,and doesn't paint the transmissions from SeaMe type target enhancers. Or from distress homing devices. Would be happy to be shown wrong,for the new technology looks brilliant otherwise,cheers Jerry.

 

[timbartlett]

HD (in various variants from Garmin, Raymarine and Furuno) is pulsed radar with software tweaks to enhance the performance. In crude terms, the more you pay, the cleverer the software you get, and the better the picture.

FMCW is a completely different technology, using very long pulses (so long that they can hardly be called pulses) at very low power, and constantly changing frequency. The first version was brilliant at very short ranges, but very poor at longer ranges. 3G is 65% more powerful, (so it goes some way towards addressingthe range weakness, and 4G uses digital signal processing to achieve the same kind of enhancements that HD achieves for pulsed radar.

 

[Ex-SolentBoy]

I am a great believer I picking a supplier and sticking with them. They all catch up eventually, and these days most enhancements are free software upgrades. The Garmin system I have now is very much improved from the one I bought several years ago.

The differences in radar picture do not outweigh the disadvantages of non integrated radar/sensors/instruments/plotters IMHO.

 

[grumpy_o_g]

HD is really a marketing term, I suspect applied when the manufacturers switched to digitally processed signals. In simple terms there's two types of yacht radar - "traditional" and Broadband. Traditional radar is a form of pulse radar, where a pulse of radio waves is sent out from the scanner and the time it takes to return is measured. The bearing is obtained from the direction the scanner is pointing when the pulse is sent and the range from the time difference between transmitting the pulse and receiving the reflected echo.

Broadband radar is Navico Group's name for FMCW radar. Normally FMCW tramsmits a continuous beam that goes up and down in pitch. With FMCW, by the time the echo has returned to the scanner, the frequency it's transmitting will have changed a bit. By comparing the frequency change you can get a very accurate idea of the time the beam took to return and therefore the range. In practice the Navico FMCW's don't transmit a continuous pulse but you can treat them as if they do. Like a pulse radar, the bearing is taken from the direction in which the scanner is pointing when the echo is received. The 3G, 4G thing is just like the iPhone really. Just updates and improved spec of the same basic techology.

That's the sharp end. At the back end the signals have to be converted into something you can understand on the screen. Analogue radar simply displays whatever it receives on your screen. Bit of an over-simplification as it can do limited filtering etc. (the gain and clutter controls, for example); basically though it faithfully replicates what the scanner receives on your screen. Digital processing on a pulse radar changes things somewhat. This is rather like the red-eye filter, face detection, noise reduction, etc. on a fancy compact camera. The radar actually has a computer that runs a program that interprets what the scanner sees into what is mostly likely actually to be there. For example an inconsistent return all the way out to the maximum range is more likely to be sea clutter than lots of boats appearing and disappearing so it may tune the returns out for you, either because it's clever enough to so it for you or because you've turned the clutter control down. On an Analogue set that would mean actually reducing the strength of the signal with the gain control and therefore possibly removing a weak but consistent return. With a digital set, even if it's manually adjusted, the clutter can be removed without actually reducing the signal strength. Navico's "Broadband" FMCW sets are all digitally processed.

Basically your choices are between digitally processed pulse radar (Garmin, Raymarine, Furuno, etc. plus Simrad's own pulse radar) and Navico's (Lowrance, Simrad, B&G) Broadband FMCW sets. Both have pro's and cons.

Broadband is very low power so you have zero chance of frying your brains even if your scanner is a few feet from your head. The low power also means that it doesn't need a Magnetron and can therefore come on almost instantly or use virtually no power in standby.

The low power means that it doesn't have quite the same range as most pulse radars. As far as I know the main difference between the 3G and 4G models is the power and therefore range. The 4G is still a fraction the power of a pulse radar but has a range of around 12 miles as opposed to 9 miles max.

Just like trying to use a searchlight at close range a powerful pulse radar can swamp everything nearby with the strength of the return (known as the bang). FMCW has incredibly good definition right down to 30 metres or so. I've seen small mooring buoys accurately returned at close range even though they were plastic (presumably the metal ring?). The very latest Raymarine's are rumoured to be almost as good but I haven't seen them.

Because SART's and active radar reflectors such as Sea-Me and EchoMax are designed to be triggered by the particular pulse pattern and frequency of a traditional X-band pulse radar, Broadband will not trigger these.

Navico's Broadband is not as good at picking storm cells and rain clouds out as the pulse radars but is better at spotting birds feeding usually I think (if you're a fisherman).

The Broadband radome is a smaller diameter than the equivalent pulse Radar. You'd really need a 24" Raymarine "HD" (i.e. the latest digitally processed set) scanner to get near the definition of a Broadband set. Windage isn't much different as the Broadband radome is taller, or weight I believe, but the diameter may be critical if you struggle to get the genny round and you're mast mounting.

I really like the Broadband Radar (I've used/played with Lowrance and Simrad 2G and 3G versions - the only difference is the MFD you display it on). As Solentboy says though, I don't think any of them are different enough to warrant a complete refit and even then there's other aspects of each manufacturer to consider. On a Maxi 1000 I'd also put a lot of money into getting a good heading sensor and rate gyro - that will improve both autopilot and radar immeasurably (in fact MARPA won't work without it). I'm always happy to spend other people's money so maybe something like the AirMar PB200 would be worth thinking about as well?

The one thing I forgot to mention was to have a look at www.panbo.com. Basically this is a specialist site for boating electronics geeks that still manages to provide a tom of usueful information for people who aren't heavily into electronics and such things.

 

[Skylark]

That's a very thorough explanation gog, many thanks.

I had two Lowrance plotters, pedestal and nav station, fitted last year and each has independant access to the 3G BB radar

This kit replaced the original Raymarine, an RL70, for the simple reason that the pedestal plotter size was the closest to being interchangeable, therefore easiest to fit without major reconstruction work.

I agree with your comment about range. I still have only limited experience with my set up but even in calm conditions, I don't think its very useable beyond 5m, a little disappointing.

 

[AlanM]

Thanks

Thanks everyone - a very comprehensive and understandable reply from Gog - much appreciated.

For info, I understand that YM is to have a review of HD radar in the March edition (out Feb).

Thanks again

Alan

 

[earlybird]

...
The Broadband radome is a smaller diameter than the equivalent pulse Radar. You'd really need a 24" Raymarine "HD" (i.e. the latest digitally processed set) scanner to get near the definition of a Broadband set.

Why is that?
Isn't definition of a pulse radar determined primarily by the beam width, which is inversely proportional to scanner size?
Is Broadband radar different in this respect?

 

[whipper_snapper]

Broadband is very low power so you have zero chance of frying your brains even if your scanner is a few feet from your head. The low power also means that it doesn't need a Magnetron and can therefore come on almost instantly or use virtually no power in standby.

Thanks, very interesting. Does that mean that the overall power consumption of broadband is lower than traditional pulsed radar ? Or does the fact that it is always transmitting outweigh the lower transmit power ?

 

[timbartlett]

Why is that?
Isn't definition of a pulse radar determined primarily by the beam width, which is inversely proportional to scanner size?
Is Broadband radar different in this respect?

Ye canna' change the laws o' physics.

Bearing discrimination is essentially determined by the (nominal) horizontal beamwidth, but nowadays the effective discrimination is significantly affected by the digital processing that goes on after the echo has returned. That is true of both pulsed and FMCW radars. The beamwidth of the FMCW radar is what you'd expect of such a small diameter scanner (big!) but the screen image is subject to very effective processing

Thanks, very interesting. Does that mean that the overall power consumption of broadband is lower than traditional pulsed radar ? Or does the fact that it is always transmitting outweigh the lower transmit power ?

It's not "always" transmitting, but it is transmitting for a lot longer than a pulsed radar. But a pulsed radar typically transmits for so little of the time (usually less than 0.1%) that even if the peak power transmitted is 4kW, theaverage powertransmitted is <4W. In other words, most of the power used by "a radar" is doing other things -- such as lighting the display, running the processor, and turning the scanner. An FMCW radar still has to do all those things. So although the power consumption of an FMCW radar is slightly lower than for a comparable pulsed radar, it isn't anything like as much lower as you you might expect.

 

[Conachair]

4G review

http://www.panbo.com/archives/2011/12/simrad_broadband_radar_4g_hands-on_1.html

 

[grumpy_o_g]

Why is that?
Isn't definition of a pulse radar determined primarily by the beam width, which is inversely proportional to scanner size?
Is Broadband radar different in this respect?

Yes and no. Both pulse and FMCW will improve definition as the beam width decreases, and that depends on the scanner size so yes. You can cheat this to an extent by digital processing though on both pulse and FMCW. Raymarine and Furuno do a good job at this. FMCW is particularly easy to enhance though as the frequency is constantly changing so you get a different pitch at the point the beam first hits and when the return stops. I have no idea exactly what algorithms Navico or any of the others use for their processing (they're normally pretty closely guarded secrets, whether commercial or military) but this is an accepted technique which works for FMCW only of course.

If you have money you can also get fancy antennae to control the beam but these are really just for avionics or military. If you're going to pay tens of thousands for a radar scanner for a yacht it's odds on the yacht is big enough for a couple of large arrays anyway...

The real reason I say a 24" radome is because the smaller pulse scanners aren't sensitive enough to pick up high definition close in because of the high power of the pulse. Think of it as trying to discern detail in music when your radio is at full volume. Exactly what part of the chain is casing the weak link in the smaller systems I don't know. It may be scanner size but remember the signal is at least partially processed inside the radome these days as well.

 

[grumpy_o_g]

Thanks, very interesting. Does that mean that the overall power consumption of broadband is lower than traditional pulsed radar ? Or does the fact that it is always transmitting outweigh the lower transmit power ?

I'd check the spec for each example but in general yes. Remember a 10 or 12" MFD will draw a fair whack of power itself by the way. I would imagine one of the main reasons Navico actually decided to transmit FMCW in bursts is to keep power consumption as low as possible.