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NEW - Technical update- Navico have launched a new range of radar with FMCW (Broadband) technology- read the review of FMCW radar for a full review and comparison of this technology versus traditional Pulsed radar technology
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Where are we? Navigating your way with Radar
Many recreational mariners have stared blankly at the Plan Position Indicator (PPI) of a radar system and asked themselves: ‘Where are we and who is near to me that I need to avoid. And what does this image actually tell me?’
So what’s happening with Radar development and can we look forward to Radar that’s easier to use and understand?
Radar: is it really worth it?
The mysteries of radar and its use for navigation have been endlessly discussed in forums and around tables up and down the country in Yacht clubs. So, has recreational marine Radar changed and if so has it improved safety at sea or made it easier to navigate the oceans and the home waters around where we keep our boats?
Since the invention of Radar (or more specifically the invention of the magnetron used to generate the microwave energy used for radar) around the time of the 2nd World War (the timing and inventor remains a contentious issue) not much has changed in the basic technology, or has it?
Furuno, Garmin, Lowrance and Raymarine now have digital radars. And the Navico group have launched a new range of Broadband ones. However, do these new products help answer the mariner’s questions: ‘Where are we? and who do I need to avoid’. Before we try to answer this let’s go back to basics.
Traditional Radar
The main components of a modern leisure marine radar are a “scanner” and a “display”. The former includes the antenna, transmitter and receiver and the latter has whatever is necessary to turn the electrical data into an image the mariner can understand.
The scanner
Traditionally in pulsed recreational marine radar the magnetron is fired up with a high voltage spike and the resulting emission from the magnetron tube, at a frequency of 9.3 - 9.4 Ghz (X band), is channelled through a waveguide and transmitted via a rotating antenna. The rotation speed of the antenna is usually in the region of 24 or 48 rpm. A single antenna is used both to transmit a pulse of microwave energy and receive the echoes from it.
The time between the pulse being transmitted and the echo being received is used to determine the range. The angular position of the target, whether it’s a buoy or another boat, is determined by simply knowing where the antenna was pointed when the pulse was transmitted The basics are fairly straightforward.
The display
The display component of the radar receives the data after it’s been partially processed in the scanner. The data is received in the form of a B plane and the display processing converts this into a PPI as seen on the display screen.
These two stages of processing, one in the scanner and one in the display, combine to deliver the end product to the user as a readable display.
Recent Radar systems evolution
Since 2003 both incremental and more significant changes were made to radar transmitters, which we can talk about later.
During this period changes have been made to the display processing to improve the representation of the data on the display. The radar images became clearer and the representation of targets became more ‘chart like’.
Although not directly related to radar development, displays have also become multi-functional. They now display a combination of radar/chart/fishfinder/weather and Automatic Identification System (AIS) data. The ability to overlay radar on top of a chart image certainly helped users determine the difference between moving and stationary returns from targets. However, the argument that too much information can cause information overload is equally valid.
The improvements of cost effective heading sensors has brought credible MARPA functionality to the recreational marine market. In my opinion this feature is often overlooked and not given the acknowledgement its value truly deserves.
Changes in the Scanner
Regulation changes- 2003, 2006 and ongoing
We discussed earlier how traditional radar transmitters have undergone incremental and significant changes. Some of these changes were a result of the tightening of the regulations relating to spurious emission from recreational X band radar. You may remember the changes, the reduction of ‘out of band/side lobe’ emissions, in 2003. There were also follow up changes in, the reduction of ‘spurious’ emissions, 2006.
These changes impacted manufacturers and resulted in higher cost radar transmitters without any real benefit to the customers. Many manufacturers were then starting to think ahead and worry about future changes to the regulations. They were concerned with demands for further reduction of emissions that would call into question whether a magnetron based design could ever meet the regulations. This may have led to some manufacturers, such as Navico, to look at alternatives to the magnetron as the transmission source.
Scanners become intelligent
Since 2006 more significant changes have taken place in the processing of the radar echo and the control of the transmitter. These types of radar scanners have been called ‘Intelligent’ or ‘Active’ scanners. Think about the processing of the data in a radar system as a chain of events starting from the transmitted pulse and ending up as a pixel on the display. The change to an intelligent scanner has meant that more of the processing takes place in the scanner itself. The output from which is a generic communication method, such as Ethernet. The by products of this are thinner and more flexible cables between the scanner and the display.
This new intelligence in the scanner has led to manufacturers claiming their transmitters are now digital. This claim is misleading as the data processing has always been digital at some point in the chain. Recently the point at which it becomes digital has now moved from the display further up the chain to the scanner.
Is Digital a good thing?
The fact that the scanner converts the radar returns into the digital domain earlier has some advantages. Working in that domain means that more sophisticated signal processing can take place. Evidence of this can be seen in the Raymarine SHD range of radar. [image of SHD versus ordinary radar]
Raymarine were an early adopter of the ‘digital’ transmitter and added a significant portion of the processing horse power into the transmitter unit. You may think this must have led to a reduction of processing in the display, but you would be wrong. The processing requirements in the display have also increased as they are no longer dedicated radar displays, as mentioned earlier. They are multi functional or combo displays.
Digital scanners are now available from Furuno, Garmin, Lowrance, Raymarine and Simrad.
With all this in mind, we should not question if a scanner is digital or not, rather: what signal processing takes place, and how effective is it? It is important to understand that it is not the technology that matters but what the equipment designers have done with that technology. It’s the advances in the processing of the data that will lead to a more understandable radar image and a better experience for users.
Transmitters – FMCW (Broadband) versus Pulsed
We mentioned earlier that changes to transmitter regulations back in 2003 may have led manufactures to think about alternatives to the magnetron. It’s worth outlining those changes in more detail.
Due to the increased usage of the radio spectrum radar transmitters have been under attack by international committees (ITU recommendations e.g. ITU-R SM.329-10 (02/03) - Spurious emissions). The reduction in ‘spurious’ and ‘out of band’ emissions are in place today. However, further changes that would tighten the ‘adjacent out of band’ and the ‘boundary’ frequencies may have led Navico to consider the use of a Frequency Modulated Continuous Wave (FMCW) transmitter as opposed to the traditional pulsed Radar that uses magnetrons as the energy source.
But will the end user see any difference? At this point the answer is, we don’t really know. The Navico products have only been demonstrated in a controlled environment by Navico personnel. Without going into the technicalities of FMCW the following table, owed to Prof Bill Mullarkey of dB Research, summarizes the technical difference between the FMCW and Pulse technologies. (Remember this is not a comment on the implementation of either technology, it’s about the inherent differences of the technologies)
|
Inherent differences between the technologies |
||
|
Characteristic |
Broadband (FMCW) |
Pulse |
|
Short range target detection |
Better |
Worse |
|
Long range target detection |
Worse |
Better |
|
Visibility of close in targets |
Better |
Worse |
|
Target resolution in azimuth |
Same |
Same |
|
Target resolution in range |
Better |
Worse |
|
Sea clutter suppression |
Better |
Worse |
|
Power requirements |
Similar |
Similar |
|
Requires standby period |
No |
Yes |
|
Vulnerability to interference from other radars |
Difficult to solve |
Easy to solve |
|
Vulnerability to onboard reflectors |
Potentially a problem |
Not a problem |
|
Ability to activate RACON’s (Radar Beacon) and SART’s |
No |
Yes |
|
Potential for future development |
Only just begun |
Mature technology |
Image of Broadband short range
Published examples of the Navico’s broadband Radar shows the piling returns, on a very short range, much clearer image than the traditional radar image. Please note, however, that these images come from Navico publicity material.
The excitement of having a new radar technology is great and congratulations to Navico for being first. However, it’s the future potential to improve the post-processing of the data, providing the mariner with the answer to that eternal question ‘Where are we and who is near to me that I need to avoid.’, that we should all be interested in.
In the case of Broadband Radar, it is clearly one of the most exciting changes in radar in recent years and promises much, but we must reserve judgement until we see the real thing go head to head in an on water sea trial. Let us look at longer ranges, interference rejection, and power consumption. Let us check the basics.
Selecting a Radar
Marine radar used to be the major component in the recreational boaters navigational electronics. However, the advancement in electronic charting combined with the accuracy of the GPS has meant that the installation of Radar is now seen by many as secondary to a chartplotter.
So Why Radar?
It’s important to realize that Radar is the only, above water, active navigational tool available to your vessel. ”Active” means that it records and displays real live data that is relative to your boat. It can detect numerous ”targets”, such as other boats, buoys, and, in some cases, rain or a flock of birds on the sea surface. The key aspects about radar are the range (how far away and how close in to your boat) it can detect targets and how effectively it can resolve (separate) targets around the boat.
If you are new to Radar, try this explanation of the principle that captures how radar works, in the basic form. Imagine you are standing on the deck of your boat after dark. In your hands you have two flashlights. The first of which has a wide beam, low power flashlight. When you shine it out to sea you can’t see very far and if two targets, say boats, are close to each other you see them both at the same time. This is like using a small, wide beam radar, typically an 18” diameter Radome. 
You can’t see very far and you see lots of targets at the same time. (In the case of the radar, seeing lots of target at the same time results in just seeing one target on the display)
Now change to your other hand, and shine the second flashlight, which has a powerful, tightly focused narrow beam and twice the battery power. As you rotate your body to look around, you see far into the distance and you see one target, then a blank, before you see the next. This is like having a narrow beam, high power open array radar.
What do you need?
So you can see that if you want to see far (greater than 12nm) into the distance and be able to distinguish between close targets you need a radar with a narrow beam, typically less than 3 degrees and more power, say greater 4kW. Interestingly, it’s the beam width that’s more important than the power. Think about the flashlight description again and imagine keeping the power the same and then focusing the beam, you would expect to see further and achieve better resolution.
On the other hand, if your boating activities are mainly close to shore or you use your radar as an aid for short range navigation, then you should be looking for a more compact solution such as an 18” or 24” Radome. These types of radar are excellent for navigation in the 3-6nm range, which is where most people use their radar.
Other factors
Other factors to consider and ensure you understand or discuss with your installer are power requirements, antenna location (not too high or you will miss close-in targets and not too low or you would miss targets in the distance) and safety.
More advanced features to look out for
- Marpa. This is the ability of the radar and display combination to acquire and monitor other vessels, display them on the radar PPI (display) and alarm if targets are in danger of colliding with your current course.
- Alarms, sector or guard alarm. These are useful for anchorage and provide a warning if other vessels or objects are coming within the range you have defined on the display.
- Radar Overlay. If you have a chartplotter/radar combined display or system, the ability to overlay the radar onto the chart map helps the user identifies specific objects or land features.
- Automatic Identification System (AIS). If you are building a system and are considering AIS, which is capable of tracking other vessels that carry a transmitter, the ability to display these targets on the radar display will also help with safety and object recognition.
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