How The Radar Speed Detection Devices Actually Work

If you are like many people you do not enjoy getting pulled over by a police officer. One of the main reasons people get pulled over is for speeding. Police officers use radar guns to detect the speed of cars and keep us using the speed limit. They are just trying to keep the roads safe for us, but no one enjoys getting an expensive speeding ticket. Many people have chosen to get radar detectors to help alert them of a police officer. Even though many people have these radar detectors not many understand how they work.
The first type of radar gun available to police officers uses radio waves. This type of radar sends the radio wave to target and back. Since radio waves move at a constant speed the radar can determine how far the target is based on the time it takes the waves to return. When the target is moving there is a change in the frequency that is detected by the radar and changed into miles per hour. Sounds like a lot of work, especially if you think about how fast it does all this. By the time you see the police officer chances are he already knows how fast you are going and can pull you over.
The second type of radar gun available to police officers uses lasers. This type of radar uses the amount of time it takes the infrared light to get from the radar to the car and back to determine speed. Once the radar knows the amount of time it takes the light to return it multiplies it by the speed of light. Since this radar can send multiple beams of light to multiple distances it is easy for it to determine how fast you are going by comparing your speed with the other objects. This radar can detect you from farther away since it uses such a concentrated beam of light.
When investing in a radar detector you have a couple options available. You used to only be able to get radar detectors that alerted you when it sensed the radio waves from the police officers radar. Now you can purchase detectors that also have a light sensitive panel that will detect the laser radar that is becoming more popular. The only problem is that since the beam of light the police officers use is so focused even with a detector it is still easy to get caught speeding. By the time your radar detects the light from the officer's radar you are already in the sight of his radar and thus already busted.
You can now also purchase radar detectors that not only detect the officer's signal, but jam it as well. When your detector gets a signal from the police radar gun it will mix it with other radio noise and confuse the officers radar. This confusion prevents the officer from getting an accurate reading of you speed. For the laser radar the detector does almost the same thing. The difference with the laser detector is that it sends a light beam of its own to the officer's radar. This also causes the receiver to be confused since it can't recognize your light beam and prevents the radar from getting an accurate reading.
Gregg Hall is an author living in Navarre Florida. Find more about this as well as Discount Radar Detectors at http://www.radarlaserdetectorsonline.com.
Accessory Kit for Escort Radar Detectors
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How to Choose a Radar Jamming Device

Radar detectors come in all shapes and sizes, but may not be effective enough to work to protect you against costly speeding tickets. Many motorists choose to invest in radar jamming devices instead of radar detectors that may leave your car unaware of potential speed traps, police officers, or state troopers waiting to ticket speeding.
Radar detectors do just that--detect radar beams that are being distributed from the radar guns of police officers or state troopers. If these radar guns are incompatible with the specific brand or type of radar detector your purchase, you will be left unaware of potential speed traps. Furthermore, radar detectors can be tricked by other items that are not meant to detect speeders. These false alarms can be annoying and still leave you open for potential speeding tickets that can not only wreck havoc on your wallet, but also your driving record and car insurance policy.
Radar jamming devices, again, work as named. These devices work to literally jam radar guns, so that police officers or state troopers will be unable to directly pinpoint your speed. Instead of radar detectors that can be tricked or evaded by the radar guns, a radar jamming device has to capability to work against the majority of radar guns used by law enforcement officials on the highways and roadways of this country.
Remember, even though your vehicle is equipped with a radar jamming device, you may still be at risk for speeding tickets. Although the radar gun of a police officer or state trooper may be jammed, most law enforcement officials are able to identify if a vehicle is speeding excessively, which can still result in a ticket. Furthermore, radar jamming devices may allow you certain leeway with law enforcement officials, but you should still abide by the posted speed limit in order to operate your vehicle in the safest manner possible.
If you are in the market for a radar jamming device, begin by setting an approximate budget for your purchase. This budget will allow you to easily find a radar jamming device that will work for your specific circumstances. Keep in mind that top of the line electronics may not necessarily be the best option for you. Look to purchase a quality piece of electronic equipment that will not break the bank.
Since a radar jamming device is a piece of electronic equipment, you should be sure to find a quality product that comes with a reputable warranty. This warranty will allow you to protect your investment in the event of malfunction or accident, so that your device can be repaired or completely replaced at little or no charge.
Ensure the radar jamming device your plan to purchase has an adequate range. Make an inquiry to the distance of the device so that your radar jamming device will be able to protect you from radar guns around every turn. Furthermore, ensure your device will work in a variety of environments, including sun, rain, and even snow.
Finally, when choosing a radar jamming device, you should be completely aware of the legal laws of your state or city. Just as with radar detectors, radar jamming devices are illegal in some areas and many states have completely blocked the use of these anti-radar items. If radar detectors or radar jamming devices are considered illegal in your state, motorists with a forbidden device in their vehicle can rack up a phenomenal fee. If your state has anti radar detectors or radar jamming devices, be sure to abide by the laws and avoid purchasing or installing either of these electronic items for your own good.
Accessory Kit for Escort Radar Detectors

Information About Radar Detectors

Radar detector models nowadays are the result of combining trouble-free ergonomic designs with state-of-the-art technology. They provide motorists with inexpensive, much needed protection from troublesome speeding tickets and hazards on the road.
How are radar detectors able to this?
From the name itself, radar detectors detect beams that usually come from police radar, which measures the speed by which vehicles are traveling on the road. A radar detector will provide a warning signal even before the police radar can measure the vehicle's speed, buying the motorist some time to adjust his driving speed and be saved from a speeding ticket.
What should you look out for a radar detector?
The Type. A radar detector has three types, namely remote-mount, corded, and cordless.
A remote-mount detector is mounted permanently to your car, ensuring an installation that is clean and almost undetectable by thieves.
A corded detector is usually mounted on the car's windshield using suction cups and is considered to provide the best kind of protection.
A cordless detector, on the other hand, is easily transported between cars, and gives an installation that is cleaner than its corded counterparts.
City Mode. City mode is a very important feature because it lessens the sensitivity of your radar detector, especially in the city, such that you get a lesser number of false alerts.
Laser Detection. A radar detector with a laser sensor detects beams in front of the car, but not on your sides or behind. Three hundred sixty degrees of laser detection, on the other hand, assures you of more protection since there are a couple of sensors to watch out for pulses on your sides, as well as the rear. It is more reliable, but of course, more costly.
Spectre and VG-2 Protection. These shielding features are important since they inform the motorist if the police have a Radar Detector Detector (RDD). Spectre is considered as a more sophisticated RDD technology and is being used by several Canadian states. Some detector models provide Stealth, a kind of protection that warns the driver and turns off the radar detector. Pricier models provide Invisible, a kind of protection that shields the radar detectors from Spectre, VG-2, or both, such that they will continue working without being traced.
Digital Voice Alert. More modern versions are equipped with digital voice alerts that will inform the driver of any laser, beam, or pulse that they were able to pick up. No need for the hurried motorist to take his eyes off the road and examine the display of your radar detector.
Instant-On Protection. The truth is you can no longer defend yourself if Instant-On radar has already been aimed at your vehicle. Your speed will already have been measured by the time you are alerted by your radar detector. However, if another vehicle was the target of radar, a radar detector with Instant-On Protection will be more K-band receptive and sensitive, such that you will be alerted right on time to slow down. It is this K-band receptivity that allows manufacturer promotion of Instant-On Protection from radars.
There you go - everything you need to know about the benefits of using radar detectors, how they work, as well as the features that you should look out for in them. Go ahead. Make yourself and your vehicle safe.
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Marine Electronics: Using Marine RADAR

Marine radar (Radio Detection and Ranging) is used to detect objects and their position relative to your location. It works by sending out a radio signal. When the signal hits an object it is reflected back to the radar unit which can then calculate the bearing of the object.
A marine radar device is an essential navigation aid for boaters. It is useful for detecting boats, birds landmasses, and weather systems even when visibility conditions are less than favorable.
Marine Radar: Top Features to Look For
The two most important features of any marine radar device are the transmitter power and the beam angle. Power can range from 2 to 4 Kilowatts. The higher the power, the better your transmitter can see through fog and rain and the further the signal can reach. Power is a factor in how well your radar does in bad weather. Blinding rain can cause low power marine radar to be less than effective.
Beam angle is determined by the size of your marine radar's antenna. A long antenna will produce a narrow beam that gives good discrimination between objects close together. A short antenna has a wider beam angle allowing the radar to scan a wider area at one time. Antennas are often customizable or configurable and can be purchased separately.
Guard Zone Alarm
Most marine radars allow you to set a guard zone around your boat. You specify the safety distance and set an alarm. If your vessel detects a buoy, landmass or other obstacle within the proximity of your guard zone, the alarm sounds.
Split Screen Displays
Split screen displays allow you to monitor objects close to your boat and objects further away at the same time. This feature is useful, among other things, for navigating buoys as you leave the shoreline while heading out towards a more distant spot.
Best Use of Marine Radar
One of the best features of marine radar is its ability to determine where you are with respect to where you were a few minutes ago. This "echo trail" feature can be used to determine how well you are navigating an obstacle as well as how well you maintaining the bearing you have set for your vessel. The echo trail is displayed on the radar's display screen so you can quickly assess visually what is going on.
Integrated Marine Radar and GPS/Chartplotters
Marine radars are fairly expensive; many units run in the thousands of dollars. It is a good idea to talk with other boaters and see what they are using and what features they like before committing that much money. To get more bang for the buck, look for marine radars that are already incorporated into other marine electronics such as GPS units and Chartplotters. Integrating your marine components reduces the complexity of your visual displays and reduces overall cost of items. Even though sometimes you have to compromise with the features of each component offered in the integrated package, integrated marine radars offer good value for hobbyist boaters.
Tracking other vessels with Marine Radar Systems
Whether you are at sea on a relaxing sailing holiday, engaged in a commercial fishing trip hundreds of miles off shore, or carrying freight from one location to another, keeping track of any other objects such as other boats and larger ships in the area is essential if you want to maximize your safety on the water. By using one of the latest generation of marine radar systems, you will be able to take advantage of a number of technologies that make tracking other vessels easier than ever, and even mark their positions and routes on the screen.
The sea can be a cruel mistress, and a change in conditions can come on pretty much instantly. One minute you can be scudding along over practically smooth water, the next, a fog can come down obscuring the world around you, and you can be battling against thirty foot waves and high winds.
This ever changing nature of the ocean means that as conditions change you can face different challenges that can impinge upon your safety. The key to ensuring that you remain as safe as possible is to remove as many of the factors that can change from the overall picture.
Other vessels are often the biggest threat any seaman can face. Smaller boats in particular are often not picked up by the radar systems of large container ships and cruise liners, and this can make things quite dangerous. It is incumbent upon all sailors to keep a check on the sea conditions around them in order to stay safe from other vessels.
Thankfully, even the fastest ships do not usually move at more than about 25 knots, which means that if you have a radar that covers 50 nautical miles, you will have roughly 30 minutes from the moment when you first make contact with another vessel until the time when you would meet, which should give you plenty of time to react and plan your navigation accordingly.
If you package together a high-speed antenna with a large format radar screen, you will be able to get a very detailed picture of what events are going on around you. A modern radar array like the Furuno 1932MK2 will allow you to enjoy a 10" screen that provides plenty of scope to see what is happening. The whole Furuno range are well known for the high quality of their equipment, and the regularly updated range boasts the latest technology, and is always at the cutting edge of marine radar systems.
One of the great things about modern marine radar systems like the Furuno is that they plot the relative position of other ships over time. Rather than being just abstract dots on the screen which convey little information, other vessels appear as a track through the area. Their movements are shown in clear detail, allowing you to easily gauge which other vessels pose a threat to you and take appropriate action.
When you are at sea and out of sight of land, your safety should always be your priority, so rather than leaving your own safety up to the actions of other people, you can keep yourself safest by having a marine radar system that works, and make your course corrections based on the up to date information that it provides.
By learning to read the information provided by your marine radar system, you will be able to make informed decisions about how to navigate, in order to best avoid trouble at sea. Knowing what is approaching you and what is happening beyond your visual range will allow you to be certain that you are safe, and also able to react in a timely manner to anything that happens, whether it is a weather system, a super tanker, or even a wave..
It is important to know what other vessels are doing, but it is also important to keep tabs on what you are doing. By tracking your own progress across the ocean, and taking the time to do the same for other boats by using a marine radar plotter like the Furuno 1932MK2, which has a 10 inch screen, you will be able to protect your boat, crew and passengers in the most effective way possible.
Instructions
Things You'll Need:
Operating manual for your radar unit
Step 1
Set the range rings of the radar. Usually, this is accomplished with a switch or dial on the unit; most units can be adjusted to cover a range from 1/4 mile to over 48 miles. The most useful settings are 4 to 6 miles for a small boat on open water and 1 to 2 miles (or less) on lakes or rivers. Shorter ranges give a more immediate picture of the situation surrounding a boat in close quarters.
Step 2
Use the Variable Ring Marker, or VRM, to determine the distance to a particular target, such as the mouth of a river, a sea buoy marking a channel entrance or another vessel. The VRM is like a standard range ring, but can be adjusted by a control (usually a knob) on the radar display so that it can be "moved" to a target. The VRM distance display will show the exact distance to the target.
Step 3
Use the Electronic Bearing Line (EBL) to determine the exact relative bearing to a target. The EBL, like the VRM, is adjusted by a knob on the display, allowing the EBL to be moved to a target and to display the exact bearing relative to the direction of your boat's travel.
Step 4
Use the EBL and VRM together to determine if a target is moving toward you in a "crossing situation" that will require your action. Put the VRM and EBL on the target; they will intersect at the target's location. If the range decreases but the relative bearing does not, the target is a vessel and a crossing situation is developing. If the range decreases and the relative bearing changes, a crossing situation is unlikely, but the prudent mariner will take care to maintain watch for the unexpected.
Step 5
Always trust your eyes before you trust the radar. Maritime law, the Rules of the Road for Inland Navigation and the Regulations for the Prevention of Collision at Sea, take no notice of radar except as a navigational aid, and then insist that decisions based on radar observations be confirmed visually. The ultimate responsibility for safe navigation rests with the master, not the radar, and numerous court cases cited in the Rules affirm this fact.
Read more: How to Read Marine RADAR | eHow.com http://www.ehow.com/how_5084999_read-marine-radar.html#ixzz0w1bObU4R
The Coast Guard's weather broadcast on your boat's radio may warn you of impending "heavy weather," but tracking an approaching storm's progress on your boat's radar allows you to take substantial action early enough to avoid the property damage and loss of life that a storm on the water can bring. Even after you make port, if you remain aboard your vessel (assuming your boat has a weather-tight cabin), you can still track the storm with your radar unit; should the storm blow itself out, either abandon your activities or enjoy the calm seas that follow.
Difficulty: Moderate
Instructions
Things You'll Need:
Stopwatch Calculator
Step 1
Change your radar's range to 48 nautical miles when you become aware of the storm visually or by radio broadcast. At 48 miles, your radar won't pick up anything below 1,200 feet in height, so you'll see the largest part of the storm. Once you've ascertained the general size of the storm, reduce the range of your radar until the edge of the storm is visible.
Step 2
Turn the "VRM" knob on your radar to set your radar's Variable Ring Marker on the edge of the storm. This will display a single ring that can be moved with the knob. Its range will be displayed in one corner of the screen. Note the range to the storm's edge.
Step 3
Start your stopwatch for a three-minute count and note the range of the variable ring marker. If the storm enters the area in less than three minutes, stop your stopwatch and decrease the range of the VRM until the line is again touching the edge of the storm. Note the new range of the variable ring marker.
Step 4
Subtract the new range from the original range to the storm; this is how far the storm traveled in the time recorded by your stopwatch. For example, 12.5 miles (original range) - 10.2 miles (new range) = 2.3 miles. If it took the storm 2.5 minutes to go 2.3 miles, then divide the distance traveled by the time and multiply the result by 60. For example, 2.3 (the distance traveled) / 2.5 (the time it took for the storm to travel the distance) = 0.92. Multiply the result by 60 to determine the relative speed (the storm's speed relative to your boat) of the storm. In this example, 0.92 x 60 = 55.2 miles per hour.
Step 5
Note the storm's apparent direction of movement, relative to your course, on your radar by turning the knob marked "EBL," or electronic bearing line, until the EBL parallels the course of the storm. Note the bearing indicated (also in the corner of the screen, similar to the VRM). This is the relative bearing of the storm.
Step 6
Subtract the relative bearing of the storm (the EBL bearing) from your course with your calculator. If your course is 245 degrees, and the electronic bearing line shows the course of the storm as paralleling the EBL set at 290 degrees, then 245 - 290 = -45. Add this to your course to determine the true course of the storm. In this example, 245 + (-45) = 200 degrees.
Read more: How to Use Marine Radar for Storm Tracking | eHow.com http://www.ehow.com/how_5872005_use-marine-radar-storm-tracking.html#ixzz0w1bV0k3G
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Whistler XTR-690SE Radar Detector

Introduction to Radar Detectors

A radar detector is an electronic device used by motorists to determine whether their speed is being observed or not by a police officer. The objective of a radar detector is to protect the motorist from getting a speeding ticket from the officer who is using a radar gun.
Radar detectors were introduced in the early 1970's. The term radar detector originated from technologies that were used earlier to detect speed.
Now the question arises, "What is radar?" Radar is a system used to measure the speed and location of any object. This system consists of two important parts - a transmitter and a receiver. The radio transmitter causes voltage fluctuation by oscillating an electric current at a predefined frequency. This oscillation of the electric field generates electromagnetic energy. This electromagnetic energy propagates in the air as electromagnetic waves. A transmitter consists of an amplifier and an antenna. While the former increases the power of electromagnetic energy, the latter transits it into the air.
The basic function of radar is to determine its distance from the destined object. For this function, the radar device emits concerted radio waves to observe any echo. If any object comes in the way of the radio waves, then it can be easily detected by radar with the help of electromagnetic energy. Radio waves constantly travel in the air at the speed of light. The distance of the object from the radar is determined by observing the time taken by the radio waves to return.
For measuring the actual speed of any object, radar can be used with a fact called Doppler shift. When any moving object passes in front of the radar, its echo will reflect the signals of the radar. The time taken by the radio signals to return after striking the object, and the frequency with which they travel, gives the actual speed of that object. If an object is coming towards the radar, then the signals will come back in a shorter period of time. It will increase the frequency and tells the actual time in which an object will cross the radar. This process depends on how fast the frequency will change. Traffic police use radar in the form of a radar gun, which is either hand-held or vehicle mounted, to detect speeding vehicles.
A basic radar detector detects police radar with just a simple radio receiver. In contrast, detectors that are more sophisticated comprise of a basic receiver along with a radio transmitter. A jamming signal is produced via this transmitter. It blends the signal of the police radar gun with extra radio noise. Due to this, a perplexed echo signal is received by the police radar gun, and the exact speed-reading cannot be taken.
Light-sensitive panels are being used in modern detectors which detect the beams from police laser guns. Lidar is difficult to avoid due to its concentrated beam, so it is quite possible that by the time the detector is able to detect it, the vehicle is in the beam's sight already. For that, speeders also use a laser jammer. It works much like a radar jammer.
In conclusion, there are several systems available to detect radar, but none of these systems is a sure shot way to get protected against speed detectors. However, one thing that can be done to avoid speeding tickets is to 'slow down'.
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Whistler XTR-590G Radar Detector

MPH Radar Detector Speed Watch

Are you searching for the precise radar detector? Well we have a list of the all the popular radar detectors also which contains some of the most famous features also. If we have to provide you the opinion we will suggest you to have the radar detectors of the Escort 8500 x 50, Beltronics STi Driver and the Escort 9500i. At present you can find a variety of Mph radar detector speed watches which help detecting the radars. Mph radar detector speed watch can be considered as a technical advancement in this field. When the comparison of radar detectors takes place these are the detectors which are very famous and most commonly used. These radars are easily available in the market and will cost you around $299.95., for some of the purchasers this range can be out of their pockets. After having the comparison of radar detectors we places these 3 radars on the top as they provides the longest ranges and also offers all sort of the protections. These 3 radars detectors are upgradeable and therefore will not be outdated. The Mph radar detector speed watch is impressively innovative and thus are commonly used.
If you are living in the areas where the radar detectors are considered as illegal then you can certainly afford which contains the price $449.95 then of purchasing the unit of Beltronics STi. In the regions where the use of the radar detectors is termed as illegal the enforcement uses the RDD's for finding the vehicles that uses the radar detectors. If the comparison of radar detectors is made there is only the one radar detector i.e. Beltronics STi Driver which is available in the market and also contains the power to immune from all the technologies of the RDD. If you did not travel to all these areas than the best option for you is to choose the Beltronics RX 65 which is cheaper from the other devices and will cost you around $120 and also is the best choice for you when the price comparison of radar detectors takes place.
If the person is looking for the new detectors we will suggest you to have the radar which has the long range, with the protection of the POP mode and also the radar with the Firmware Upgradeable. The mode of the POP is the usual Ka or K band signal of the radar that travels from gun of the radar to target and comes back in a very less time of the 1/10 second. When there is comparison of radar detectors it should be noted that the cheap detectors are not able to see that signals as it works so fast. This is a growing technology and lots of the latest models provide the protection to this latest technology. The firmware Upgradeable is only available in some of the radar detectors which are very much expensive when the comparison of radar detectors is made with the other.
Gary Pearson is an accomplished niche website developer and author.
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Marine Radar

Leisure marine radar is quite unlike any of the other electronic navigation aids. Not only is it more expensive to buy and more demanding of electrical power, but it also requires more skill on the part of the operator to set it up and adjust it to suit prevailing conditions and to interpret the picture on its screen. In return it is the most versatile of all electronic aids.
The basic principle of yacht radar is similar to that of an echo sounder: it transmits pulses of energy and measures the time that elapses before the echo of each one returns. One major difference is that instead of using ultrasonic sound, radar uses extremely high frequency radio waves, called microwaves - in the order of 9.5 GHz (9500 MHz) and with a wavelength of about 3 cm. The other big difference is that instead of being transmitted downwards, like the ultrasonic clicks of echo sounders, radar microwave pulses are focused into a beam by a rotating aerial and transmitted horizontally through 360° around the boat.
So a boat radar is able to measure the range of a target from the time it takes a microwave pulse to make the out and back trip, and measures the target's bearing from the direction that the scanner is pointing. This information is used to build up a picture on the display - sometimes called a PPI or 'plan position indicator', because the overall effect is rather like a plan, or bird's-eye view, of the boat's surroundings.
All radars have seven main controls:
On/standby/transmit
The on/standby/transmit control is used to turn the set on. It will have to be left in its standby mode for at least a minute or two while the magnetron - the component that actually generates the microwaves - warms up, so on most modern sets this warm-up period is indicated by a count-down timer on the screen. Once the warm-up is completed, switching to transmit mode turns the transmitter on.
Brilliance
The brilliance control determines the brightness of the picture exactly like the corresponding control on a domestic television set, and should be adjusted to give a clear but not dazzling image. On radars with a liquid crystal display, the brilliance control has to be used in conjunction with the contrast setting; the two are interdependent, and their adjustment depends on the angle from which you are looking at the screen.
Gain
Gain refers to the amount of amplification applied to the returning echo. In some ways it is easy to confuse the effect of the gain control with that of brilliance, because turning it up makes weak contacts look bigger, brighter and more consistent. The two are not interchangeable, however: brilliance is adjusted to make the picture clearer or more comfortable to look at; whereas the setting of the gain control can determine whether some contacts appear at all. As a rule, the gain should be turned up until the screen is filled with a background speckle, then turned down until the speckle just disappears, but it may need to be readjusted each time the radar's operating range is changed.
Range
The range control, as its name suggests, is used to adjust the operating range of the set, typically in about eight steps from one eighth or one quarter of a mile, to between 16 and 48 miles. The range to use depends on the job in hand: short ranges (between half a mile and 4 miles) are generally of most use for pilotage; medium ranges (4, 6 or 8 miles) for collision avoidance and long ranges (8 to 24 miles) for coastal and offshore navigation. Ranges in excess of 24 miles are of very little practical use for small boat radars.
Tuning
The tuning control, like its counterpart on a domestic radio, is used to adjust the receiver to give the best possible reception of incoming signals. Returning echoes are very weak indeed, so a precise match between the transmitter and receiver is of paramount importance. The radar's tuning control offers very fine adjustment, to allow for small variations in the transmitting frequency caused mainly by variations of temperature. To tune a radar, start by setting the brilliance to a comfortable level, adjusting the gain until the background speckle just disappears, and selecting a medium range. Choose a weak contact somewhere near the edge of the screen and concentrate on that, while adjusting the gain control in small steps - allowing at least two seconds between each step - until the chosen contact is as big, bright and consistent as possible.
The adjustment of these first five controls is aimed at giving 'targets' - the physical objects that reflect radar waves - the best possible chance of appearing on the screen as 'contacts'. Two more controls are used to refine or clarify the picture, by removing unwanted contacts or clutter.
Sea clutter control
This is sometimes called STC or swept gain, and is used to remove the clutter caused by echoes from waves, that can otherwise form a bright circle or star-burst pattern in the centre of the screen.
Under normal conditions - with the sea clutter control turned right down - the radar may be receiving echoes from targets at a variety of different ranges, but with much weaker echoes from very distant targets than from targets close at hand. This means that the echoes which return very soon after each pulse has been transmitted need much less amplification than those which are received later.
The sea clutter control works by reducing the amplification of early returns even more, while leaving the later levels of amplification intact. On the screen this has the effect of obliterating weak contacts close to the boat, allowing stronger contacts to show up more clearly. If it is overdone, however, the sea clutter control is quite capable of suppressing the amplification to such an extent that even the strongest contacts - such as land - are obliterated at ranges up to several miles from the boat, so it should be used with considerable caution and always as little as is necessary.
Rain clutter
This control is sometimes known as FTC or differentiation and, as its name suggests, is used to remove the clutter caused by meteorological effects such as rain, snow or hail. A heavy rain shower can be quite an effective reflector of radar pulses, but it does not reflect them in the same way as a solid object. Instead of returning an echo which is a crisp copy of the transmitted pulse, rain echoes are weaker but more drawn out. On the screen this produces a large but relatively diffuse contact, often described as looking like a smudge or 'cotton wool'.
The rain clutter control acts by ignoring all but the leading edge of each returning echo. This effectively reduces the energy received from rain echoes to such an extent that they do not appear as a contact at all. Almost inevitably though, it reduces the energy received from real targets. The drawn out echoes produced by gently sloping coastlines such as beaches or mudflats are particularly badly affected, so the rain clutter control, like the sea clutter control, should only be used when necessary.
Interpreting the picture
The first time one looks at a boat radar screen, it often comes as something of a disappointment: the picture may look crude and blobby, and bits of the coastline may be missing, making it difficult to relate what appears on the screen to the chart of the same area. A boat radar is definitely not 'an allseeing eye' and interpreting the picture calls for practice, and a slightly deeper understanding of how the radar works.
To begin with, it may help to visualize the stream of microwave pulses leaving the radar scanner as being like the beam of a searchlight. In order to produce an echo, a target has to be 'illuminated' by the radar beam. Some materials, such as GRP, which are opaque to light are transparent to radar waves. But something such as a steel funnel in the way of the radar beam can block radar waves just as effectively as it blocks light, to cause a shadow zone which can never be illuminated. The obvious solution to this problem is to make sure that the radar scanner is mounted higher than any large metal objects on the boat. Land has a very similar effect, though without the easy cure. Bays or river entrances will be hidden from the radar by surrounding headlands just as they are hidden from the naked eye. This is the main reason why there are gaps in the radar picture of the coastline.
The biggest obstruction of all is the earth itself. There is nothing unfamiliar about the idea of things being invisible because they are 'below the horizon', nor that hills can be seen at longer ranges than low lying ground or the shoreline itself because they are tall enough to be 'above the horizon'. The same effect appears on radar: at long ranges hills may appear to be isolated islands and the true coastline may not show up at all. Microwaves bend very slightly to follow the curvature of the earth, so the radar horizon is about five per cent more distant than the visual one.
Once a target has been illuminated by the radar beam, its ability to produce an echo depends on its material, size, shape and to some extent on its surface texture. Some materials (such as GRP) are almost transparent to the microwaves. Others (such as wood) absorb microwaves. This is why yachtsmen should never assume that their GRP or wooden vessels will be 'seen' by a ship's radar. Some materials, most significantly metal, rock and water, are good reflectors of microwaves.
The effect of size is fairly obvious: in general a large target can reflect more of the radar energy than a small one, so it stands a better chance of appearing as a contact on the radar screen. The effect of size, however, is masked to some extent by the effect of shape. Spherical or cylindrical objects are poor reflectors because they scatter radar energy, instead of reflecting it back the way it came. Flat surfaces, on the other hand, can be very good reflectors indeed, because if they happen to be positioned exactly at right angles to the approaching radar beam the effect is very much like a mirror, directing the radar energy straight back to the antenna. At any other angle, however, a flat surface is likely to send the echo off in the wrong direction. The most reliable all around reflectors tend to be those with uneven surfaces, because although some of the radar energy may be scattered the rough surface almost guarantees that at least some of it will be returned.
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