Early radar antennas needed large, open radiator arrays with correspondingly large motors to turn them. These evolved into compact, enclosed antennas that weigh as little as 12 lbs. Even more dramatic has been the evolution of the display.
Older displays had a phosphorus-coated oscilloscope tube. A motor-driven PPI (Plan Position Indicator) rotated around the tube in synchronization with the antenna. Echoes were electronically generated and projected onto the phosphorous. They appeared brightly only briefly and would begin to fade as the PPI continued its rotation. A viewing hood was needed in daylight.
The first major advance in radar displays was the introduction of raster scan technology. Raster scan displays are monochrome, usually green. They convert signals from the radar antenna into a video image that can be displayed on a TV monitor. The PPI, instead of being the source of the generated blips, is simulated on the screen to coincide with the antennas rotation. The image stays on the screen for a full rotation without fading. Some modern models have a video output that can feed a conventional TV or even a VCR.
The addition of an inexpensive microprocessor enabled a raster scan radar to become a full-featured navigational computer. Accurate bearings and distances to targets can be displayed. The display can be frozen, offset or zoomed to study a particular situation. Additional information from GPS, Loran, wind instruments etc., can be displayed with the radar image. Some new models now allow electronic charts to be displayed on the same screen as the radar image.
Despite these advances, radar displays remained quite bulky…until recently. This limitation made waterproofing difficult and relegated radar displays to mostly belowdecks installation, requiring crew to relay information to the helm.
This final problem was solved by the introduction of liquid crystal displays (LCD) instead of CRTs (cathode ray tubes). Early LCD radar such as the Apelco LDR9910 had many shortcomings. They lacked good resolution, had very poor contrast, were easily affected by heat and cold, and could display images at only one brightness level, thus making it impossible to differentiate between strong and weak echoes.
The evolution of laptop computers brought about great advances in LCD screen technology. These new displays can reproduce virtually any image that can be shown on a color CRT monitor. The application of these displays to compact radar finally solved the problem of bulkiness and excessive power consumption.
LCD displays can be made flatter than CRT displays. They do not require high operating voltages and can be made weather-resistant. Their power consumption is also much less. The current batch of LCD display radar represents the third generation of such models. The manufacturers have improved display resolution and decreased prices. Their antennas and attached transceivers, however, have remained essentially unchanged from previous versions.
The only specification most radar boaters look at is maximum range. How better to impress your boating friends than to have a 48 mile range radar! As weve said before, however, you probably won't ever be able to see that far. What matters more are some of the radars other specifications. An explanation of these follows:
Maximum Range. A radars maximum range is only attainable if it is mounted sufficiently high enough to see that far. A 16- or 24-mile range radar set, such as those reviewed in this article, will probably be sufficient for most boat owners.
Minimum Range. A radars minimum range is partly dependent on its height above the water, as well as its vertical beam width and the amount of noise that appears in the center of the screen. The higher a radar is installed above the water, the more its minimum range is increased.
The technical specification given for minimum range is different; it is simply the shortest distance at which the radar can resolve targets as images. For example, if your minimum range is 50 meters (164′), you could not use your radar (mounted at any height) to navigate in a heavy fog between buoys that are only 200′ apart. (When between them, you could never see both at once.)
Range Discrimination. This is the distance at which a radar can distinguish two broadside targets that are in line with each other. For example: If a tugboat and the barge it is pulling are closer than the range discrimination specification, you won't be able to tell them apart. A radars range discrimination is dependent on the length of the radar pulses it emits. A smaller range discrimination ability is better than a larger one.
Bearing Accuracy. Radar should be able to produce relative bearings with an accuracy of +/- 1 to 2. Keepin mind that these bearings are relative to the position of your boat and are neither magnetic nor true bearings.
Horizontal Beam Width. The signal transmitted by your radar is shaped by its antenna. Optimally, this beam should be as small as possible. However, concentrating the signal into a narrower beam requires a larger antenna. A narrower beam width allows you to differentiate targets that are closer together. This is why commercial vessels have radar antennas that are 8′ wide or even larger. The compact design of the models in our test limits their ability to separate adjacent targets. When approaching a narrow channel two boats may appear as one until you are close enough that they are separated in arc by more than the value of the radars horizontal beam width.
Vertical Beam Width. A radars vertical beam width determines how fast the signal spreads as it leaves the antenna. It also determines, in part, the minimum range of a given radar installation (the point at which its signal hits the water).
Antenna Sidelobe Attenuation. Some of the antennas emissions will escape on either side of the intended pattern. These signals are called sidelobes. When looking at large targets, some of these sidelobes may be reflected back and appear as interference. The ability of the radar to suppress these emissions is listed as a negative number (for example -21 dB) in relation to the main signal. The smaller this number (more negative), the better it is; -21 dB is better than -18 dB.
Output Power (Peak Output Power). This is the maximum peak power transmitted by the radar. Higher power is necessary to produce longer range. And higher power also produces crisper, clearer echoes.
Overall Noise Figure. A radar receiver listens to noise present in our surroundings, along with noise it generates internally. This noise accounts for the bright area seen in the center of the radar screen. It is advantageous to minimize this area. A radar with a small overall noise figure will have less of an unusable area. Additionally, they will be better able to see smaller targets with weak echoes.
Number of Quantization Levels. This refers to the number of levels of brightness that can be shown on your radar screen. On a radar with just one quantization level, all radar echoes appear with the same brightness regardless of the size of the target. This leaves you only the size of the echo to help in determining the identity of the target. Models with multiple quantization levels display some radar reflective targets as brighter echoes. For example, a large metal ship passing in front of land will appear brighter than the land behind it. The more quantization levels, the better. All three radars in this report have four levels.
Our testing of LCD radars began with the Apelco LDR9910, which, as noted, had shortcomings. In the August 15, 1996 issue, we reported on the Raytheon RL 9, Autohelm ST 50, Furuno 1621 and 821 and the Si-Tex T-150. (Raytheon owns Autohelm and so those two units were practically identical.)
Testing was done both under controlled conditions with the units mounted on a test vehicle and in a boat mounted 10′ above the water.
On the water, we set up each unit and noted its ability to see both standard and radar reflective buoys. The shape of coastlines also was noted. On land, two simulated buoys (large metal trash cans) with radar reflectors mounted on top were set up 58′ apart on an abandoned airport runway. These buoys were used to measure the radars horizontal beam angles and the accuracy of their variable range lines (VRL). As usual, each of the units was disassembled and examined for overall quality and durability in a marine environment.
Raytheon RL 72 Pathfinder
The Raytheon RL 72 is virtually the same unit as the Autohelm Z335, a replacement for the earlier ST 50+ model that costs $50 more. Unlike previous Autohelm and Raytheon models, these two are no longer made in Japan by JRC, which now markets its own LCD radar, the JRC 1000.
The Raytheon/Autohelm waterproof display console measures 8.8″ x 8″ and is 3″ deep. It has a display resolution of 320 x 240 pixels and a four-level gray scale. For comparison, a standard VGA computer monitor may be 1024 x 768 pixels or greater. Actual display size is 7″ measured diagonally. Controls are well marked and backlit. Eleven dedicated keys and a track pad are augmented by four soft keys located along the bottom of the display.
As with all radar models now on the market, these radars can display various NMEA 0183 navigational information as well as radar data. Display modes are selectable to show a conventional circular guard zone, a guard sector of selectable size, man-overboard data, a highway course/deviation display, complete navigational data or a zoomed-in view of a particular portion of the radar image. Display visibility was very good under all viewing conditions.
The Raytheon RL 72 and Autohelm Z335 are supplied with an 18″ diameter 2-kW radome transceiver that utilizes a phased array technology antenna. They are available in 4-kW, 24″ radome models called the SL 74 and Z337. The manual is excellent.
JRC Radar 1000
The JRC Radar 1000 is the companys direct entry into the low-end consumer radar market. At less than $1,000, it is unquestionably the low price market leader. The Radar 1000 also has the smallest display and radome of the models in this current test. These factors piqued our interest, making us think it might be suitable for quite small boats.
The JRC 1000s display measures 7.3″ wide by 7.1″ high and is 3.2″ thick. The actual display measures 6″ diagonally with a resolution of 320 X 240 pixels. Control of all functions is accomplished by five dedicated buttons, a Joy Stick and a push and turn Jog Dial. The Jog Dial and Joy Stick eliminate some buttons. Display visibility in differing light conditions was good. NMEA data is displayed along the bottom of its visible area. The only available display options are normal, offset and a selectable guard zone.
The JRC 1000 is supplied with a 12″, 1.5-kW radome antenna that incorporates a phased array patch antenna. It was the smallest antenna tested and weighs only 9 lbs. The 1000s antenna is also designed slightly differently than the others we tested. Its electronics are actually located in the antenna top. This design does not allow for minor problems to be repaired in place, should they occur. There is also no provision for a drain plug to drain water that may enter the radome. JRCs manual is well-written but lacks depth. We would have appreciated additional radar background information and operating tips.
The RA772UA is offered by the recently allied companies of Simrad and Robertson. It is actually built in Japan by the Anritsu Corp. Like the Autohelm and JRC units, it includes a waterproof display intended to be installed anywhere. This display measures 8″ diagonally and has a resolution of 640 X 480 pixels. It measures 8.3″ wide x 9.4″ high and is 2.8″ thick.
The RA772UA is controlled by five push-buttons and a four-way cursor key. The display remained adequately visible in all light levels. A full screen navigational information display is available that includes an arrow indication of cross-track error. NMEA 183 data is also normally shown across the bottom of the radar display. Menus are shown in a window located in the lower right-hand corner of the display.
In addition to the normal selection of radar display modes such as head up, north up or course up, the Simrad RA772UA also can produce a semi- 3-dimensional display. In this mode, the quantization levels of returned radar echoes are represented by increased height of each image displayed. According to its manufacturer, this makes it easier to discriminate between target echoes and lower level noise echoes. A combination split screen conventional and 3-D display also is available. This feature is interesting. As promised, when in 3-D mode, the size of the displayed echoes did correlate well with the sizes of the corresponding targets. However, the look of these displayed echoes did not resemble the targets shape. Any perception of being able to obtain an actual 3-D sketch of the target is incorrect. We gained the most value from this feature in bright sunlight when lower level dim targets can be washed out when displayed in the conventional gray scale quantization mode.
The RA772UA is supplied with a 2-kW, 17.7″ enclosed radome antenna. While we found the display well-made, we question the design and construction of its radome top end. Anritsu uses a plastic parabolic reflector that is fed by a waveguide horn antenna. This arrangement is very old technology, which dates back to the early days of radar in the 1940s. The performance of a small parabolic reflector arrangement such as this does not equal that of a similarly sized phased array antenna. This was especially evident in the poorer sidelobe attenuation obtained in comparison to phased array antennas. In addition, we are concerned that the plastic reflector may tend to vibrate and possibly crack with age.
General construction techniques used in the radome also showed less attention to detail than other models. For example, sticky back metal foil is used to shield wires and no attaching cord is provided to keep the radome cover from falling off if opened for service. Finally, the customary red power positive wire is used for a NMEA interface connection while white is designated positive. We don't think this arrangement was well thought out by the maker.
Radar Image. Both the Raytheon SL 72 and Simrad RA772UA produced radar images consistent with other non-LCD radars we have used tested. The JRC 1000s display did not show some smaller targets.
Display Size and Information. The Simrad radar, by a small margin, has the largest display. However, Raytheon manages its display in a more useful fashion. Autohelms treatment of navigational data and operational menus makes its display superior. Simrads 3-D viewing option is interesting but not a necessity, and not worth the added cost for this model. In our opinion, the JRCs display is too small to be functional.
Display Visibility and Illumination. All three models had good display visibility under varying light conditions. Both the Simrad and Autohelm had slightly better overall visibility than the JRC.
Tuning & Adjustments. All three radars performed satisfactorily when operated in their automatic tuning mode. However, in all cases we were able to slightly improve radar images by manual tuning. The Anritsu radar consistently produced too much gain when set to auto. It also required multiple keystrokes to adjust most functions. This was not as convenient as other models. The Raytheon radar was the easiest to tune and adjust. JRC provides only bar graphs for an indication of tuning levels with no numerical indication of the level set. This makes it difficult to return to a known level when tuning the radar.
Operational Performance. The Raytheon RL 72 is the clear leader in this category. The JRCs small display and very small antenna bring it below acceptable levels for radar performance. It consistently failed to produce results which were as good as the others tested. The Simrad performed well but lacked the resolution of the Autohelm. We attribute this to the wider beam width produced by its antenna. The Raytheon was the only one able to activate a RACON located 1.5 miles from one of our test sites.
As noted earlier, our past reviews have included models from Furuno and Si-Tex. Among other changes, the Furuno 1621 has been given a power boost from1.5 kW to 2.0 kW, and a new name-the 1621 MK11 ($1,795/$1,395). The 1621 MKII has a temperature-compensated display, faster keyboard and cursor control, and optimized 24 rpm parabolic antenna for better sidelobe reduction. The company also makes the 2-kW 821 ($2,695/$2,000) with larger display and better resolution, and the 4- kW M841 ($3,600/$2,700).
The 1.5-kW Si-Tex T-150 is still available at about $1,100 discount. New Si-Tex models include the 2-kW T-175 ($2,499/$1,850) and 4-kW T-180 ($3,149/$2,300). The Si-Tex T-175 has a new online help function.
We have always liked the Furuno LCD radars for their bright displays and many features. The Si-Tex T-150 is quite small but lacks features found on the Raytheon and Furuno models.
The Raytheon RL 72/Autohelm Z335 is our current winner for low-priced LCD radar. It currently outperforms all of the other models available in its price range, including the Furuno 1621 and Si-Tex T-150. The Simrad RA772UA was disappointing, considering that it is about $500 more than the Autohelm model. For small boats, say under 20′, one might consider the attractively priced JRC Radar 1000, but we would first take a comparative look at the nearly-as-small Si-Tex T-150.
Contacts- Raytheon/Autohelm, 676 Island Pond Rd., Manchester, NH 03109-5420; 603/647-7530. JRC, 1011 SW Klickitat Way, Bldg. B, Suite 100, Seattle, WA 98134; 206/654-5644. Simrad, 19210 33rd Ave. W., Lynwood, WA 98036; 800/426-5565.