For decades, fixed principles applied in recreational boating:
The radar is blind for the first few dozen metres around the ship,
A fine resolution is only possible with large antennas, and in poor visibility the transmitter has to run in power-hungry standby mode to be ready for use quickly. Now Furuno, Garmin, Navico and Raymarine are completely reshuffling the cards.
Thanks to advances in semiconductor production for transmitters and receivers as well as increasing computing power, completely new principles for signal generation and evaluation can now be realised.
At first glance, the new parameters even seem strange:
Previously, a radar had at least 2000 watts of transmitting power, 4000 was better, but now much less than 50 watts is supposed to be enough?
It is said to be ready for use just seconds after switching on, and screenshots show the dolphins of your own box:Advertising gags? No, with current technology this is actually possible.
The previous technology
Firstly, a very rough description of how a radar device works: It emits a signal and displays on the screen inwhat distance and from which direction its echoes can be received. The distance is calculated from theTime between sending the signal and the arrival of the echo determined. For the direction, marine radars simply use theRotate antennaThe image then shows the echo from the direction in which the antenna is currently positioned. The resolution results from the frequency used and the diameter of the antenna - the larger it is, the better.
OnPleasure craft can only accommodate devices that operate in the X-band, i.e. at around 9.5 GHz.
With a reasonable amount of civilian effort, it has so far only been possible to use a so-calledPulse radar build: It sends a short signal (pulse) and then listens for echoes. From today's perspective, a simple receiver is sufficient for this.ProblemIn order to be able to distinguish between targets in quick succession, the transmitted pulse must be very short. To ensure that the correspondingly short echoes can still be analysed, i.e. contain enough energy, they must also be transmitted at very high power, i.e. the 2 to 4 kilowatts mentioned above.
During transmission and shortly afterwardsthe receiver is deafat a very short distancethe radar sees nothing. In addition, the required power at high frequency could previously only be achieved with a special tube, the so-calledMagnetrongenerate. This takes a few minutes after switching on to reach operating temperature. To ensure that the radar was ready for use quickly in poor visibility, the magnetron had to be heated in standby mode the entire time - which costs energy.
Current radar devices
Significantly better results can be achieved if additional information is added to the transmitted signal. With theMagnetron transmitter this was not possible, here power and frequency are mechanically predetermined, butnot particularly exactt. Now the latest semiconductors are coming into play: the frequencies required for radar have recently been made possible withtransistors (solid-state technology) much more precisely and can therefore be better analysed.
In the recreational boating segment, the companyNavico under the name Broadbandthe first radar without magnetron introduced. It does not work with pulses, but transmits constantly and continuously changes the frequency - this technology is called continuous wave or FMCW.
The distance to a target is calculated from the difference between the frequencies of the currently transmitted signal and the echo. With this principle, muchLess transmission power necessary, less than half a watt. The receiver and transmitter can therefore work simultaneously, reducing the blind spot around the ship to just a few metres around the antenna. Even your own stern sea becomes visible.
The Broadband 4G is currently the third generation of this Navico radar on the market. The resolution at close range is much better than with classic pulse radar, but there are also disadvantages at long distances. Navigation aids such as RACON do not work with a continuous wave radar, but this can be easily compensated for by the map overlay that is commonplace today. Due to the low transmission power, no safety distance is required.
News on the screen
Until nowSimrad with hisSemiconductor radar alone on the market. A few months ago, all the major radar manufacturers announced the next step. Furuno, Garmin, Simrad and Raymarine are launching semiconductor devices that vary the frequency within the transmission pulse.Chirp that is.
This allows the receiver to assign individual sections of an echo to a specific time of the transmission, navigating within the echo, so to speak. Instead of a short, very intense transmission pulse, a long one with low power is now sufficient, as overlapping echoes still differ in frequency. The receiver mathematically projects the entire energy of a long echo to the time of the first arrival, so that asharp brand is created.
Overlapping echoes are separated again. This technology is called pulse compression; it requires a great deal of computing power as well as very precise and therefore expensive components in the high-frequency section and has therefore hardly been available in civilian applications until now.
Conveniently, the process automatically reducesInterferences such as rain or swell echoes and improves the sensitivity of the receiver. Pulse compression radars manage with a transmission power of 20 to 40 watts. However, long pulses alone would again have the disadvantage of a large dead zone. For this reason, pulses of different lengths are usually sent in succession. Short pulses with little energy are sufficient for close range, longer pulses with more energy for scanning greater distances.
Furuno and Garmin advertise with anew presentation: Targets approaching the ship are shown in a different colour. Earlier devices withAutomatic target tracking. But with the new generation, this function works much better, because with chirp radars the information can be derived from a single echo. This is due to theDoppler effectThe faster the reflecting object approaches, the higher the frequency of the echo. Since the new radars, in contrast to pure pulse devices, analyse the frequency anyway, the step to the display is not large. However, it takes a lot of logic and mathematics to separate the frequency shift caused by the Doppler effect from the chirp technology and to distinguish between targets that are actually moving and the harbour entrance being approached.
Models and prices
Furuno andRaymarine are aiming their new radome systems directly at pleasure craft. Furuno's DRS4D-NXT has a diameter of 61 cm.2540 Euro on the price tag. It works with the Furuno plotters of the NavNet TZtouch and TZtouch2 series.
The Raymarine Quantum measures 54 cm in diameter and costs depending on the versionfrom 1779 Euro. It works with all plotters in the a, c and e series with the latest Lighthouse software, the corresponding update is available free of charge on the Raymarine website. That's what we call service. For easy installation, Raymarine offers a WiFi connection between the plotter and radar; all you need to do is connect a power cable in the mast or on the equipment carrier - the installer will be delighted.
Garmin andSimrad initially only offer the technology as a free-rotating antenna. With a diameter of at least 1.2 metres, a whole lot of ship has to sit under the device. And the prices are also
at around6000 Euro (Simrad Halo) and 8700 Euro (Garmin Fantom) more suitable for larger boats and yachts. The Navico broadband radar in the radome is of course still available.
Suitable for the practice?
Our practical experience, for example with the Halo radar, confirms the theory: compared to the old technology, its resolution can be described as fantastic. During a test cruise on the Elbe and through Hamburg harbour, the Halo system even detected targets that were only around 5 m abeam from our own boat. The radar reflectors on buoys or in front of bridges, which are particularly important for inland skippers, were always reliably detected.
