Electronics is a vast field of study encompassing systems and technologies that control the flow of electrons and other types of charged carriers in various devices such as valves and semiconductors. The application of electronics is fairly widespread and is often the base for the growth of technology. Almost every new or old invention uses the concepts of electronics. Electronics is one of the primary branches of electrical engineering. To put electrical engineering into practice, a large number of electrical devices and equipments are required to test the workability and durability of complex electrical machines and systems.
Electronic test equipment is usually simple and cheap though there are compound electrical gears that are more difficult to test. Electronic test equipment is often referred to as test gear. These devices generate stimulus signals in order to receive responses from electronic gadgets referred to as Devices under Test (DUTs). By using these devices, the functioning of the DUTs can be proven and faults can be tracked and repaired.
Electronic test equipment can range from a simple light bulb to complex computerized and automated testing systems. There are different types of test equipment available for testing different devices. Basic electronic test equipments are used for simple measurement of the capacity of voltage and current in common circuits. Such test gear includes devices such as voltmeters, ammeters, galvanometers, ohmmeters, multimeters, power supplies, signal and pulse generators and oscilloscopes. These devices are usually digital and check simple prototypes. Certain advanced and less commonly used equipment such as clamp meters, electrometers, EMF meters, RF probes and logic analyzers are used to test the operation of higher and advanced components. Most test equipment used generate signals and hence are called signal-generating devices. Signal generating devices such as frequency synthesizer, function generator, pulse generator and signal injectors are used to generate signals for testing the working of electrical circuits.
Electrical test equipments have extensive use in fields such as aerospace, defense, automobiles and telecommunication. The use of these equipments helps in reducing the need for future quality assurance tests.
Test Equipment provides detailed information on Test Equipment, Test Equipment Rentals, Electronic Test Equipment, Used Test Equipment and more. Test Equipment is affiliated with Ultrasonic Cleaners.
Article Source: http://EzineArticles.com/?expert=Alison_Cole
Monday, September 24, 2007
Electronic Dog Doors
Because you maintain a hectic calendar, you probably have to leave your dog at home alone on many an occasion. The good thing is that dogs act as guards who keep strangers and intruders away from your property. There have been innumerable cases of burglary, however, where the dog doors were used as the point of entry. The plain hanging screen dog doors are major attractions for burglars as they prove easy to be opened. The bad thing is your poor dog needs to get in and out of the house when you’re not there.
To keep this from happening to you, buy electronic dog doors instead. Electronic dog doors are much safer because they can only be operated through the use of electronic keys. These electronic keys can be placed on the collars of your pets so that only it can gain access to the electronic passageway.
Electronic dog doors are endowed with a directional sensing system that determines the distance of the dog from the door. Information regarding the direction that the dog is going is sent to the dog door system, so it will not open when the dog is just walking around, sleeping, sitting or eating nearby. The door is only unlocked when the pet is aiming at the door’s exact direction.
Electronic dog doors are the best to use. With such a door, you can be assured that unwanted guests can never enter your home, and that all your belongings – including your dog – are always safe and secure.
Dog Doors provides detailed information on Dog Doors, Electronic Dog Doors, Patio Dog Doors, Screen Dog Doors and more. Dog Doors is affiliated with Soft Dog Crates.
Article Source: http://EzineArticles.com/?expert=Thomas_Morva
To keep this from happening to you, buy electronic dog doors instead. Electronic dog doors are much safer because they can only be operated through the use of electronic keys. These electronic keys can be placed on the collars of your pets so that only it can gain access to the electronic passageway.
Electronic dog doors are endowed with a directional sensing system that determines the distance of the dog from the door. Information regarding the direction that the dog is going is sent to the dog door system, so it will not open when the dog is just walking around, sleeping, sitting or eating nearby. The door is only unlocked when the pet is aiming at the door’s exact direction.
Electronic dog doors are the best to use. With such a door, you can be assured that unwanted guests can never enter your home, and that all your belongings – including your dog – are always safe and secure.
Dog Doors provides detailed information on Dog Doors, Electronic Dog Doors, Patio Dog Doors, Screen Dog Doors and more. Dog Doors is affiliated with Soft Dog Crates.
Article Source: http://EzineArticles.com/?expert=Thomas_Morva
Electronic Dog Fences
Electronic dog fences provide dog owners with an automated, electronic means to make sure their dogs do not go beyond the safety of their homes. It also helps dog owners make sure that their dogs do not do any inadvertent damage to other people's property.
It effectively keeps the dogs within the owner's property and helps dogs learn to know their boundaries. They are trained by the system to automatically stay away from the boundaries of the home. Electronic dog fences have the added advantage of not taking up any property space. They are totally controlled by the dog's collar, and the predefined areas the dog is allowed to stay in.
The great thing about electronic fences is the fact that they can be programmed and wired to protect other areas of your home that are prone to the playful mischief of your energetic dogs. This way you can protect fish ponds, flowerbeds, gardens, and other sensitive areas.
But how do these things work? They are pretty simple, if you come to think of it. Here is a step by step guide to how electronic dog fences are set up and used.
Your Dog's Electronic Fence
1. Area Wiring – First of all, thin antenna wires are buried around the perimeter of the areas you want off limits to your dog. These wires are usually parallel to your picket or perimeter fences that surround your property. These wires are light, not bulky and are pretty easy to install.
They can even be secured in non soil areas by means of normal attachments easily found at any hardware store. Just make sure they are safe from the elements and are not an impediment to your surroundings. These wires can be installed beside your fish pond, other pet cages, and off-limit areas.
The wiring can also be installed inside your home. It should be installed in a way that it does not become cumbersome. It can be laid out like normal cable wire. Just make sure it is secured to the walls or to stable furniture and is beyond the reach of toddlers or your pets. You could even put it under you rug or under your carpet.
2. Pet Collar – Your pet then is made to wear a special collar that can receive signals from the wires you just installed. It is this collar that acts as the fence. Your pet should be wearing the collar for the system to work. Without the collar, the electronic fence will uselessly benign.
The collar works using radio frequency and has a specially installed radio receiver to pick up signals from the antenna wires in your territory.
3. Train Your Dog – the systems sets off a very mild and harmless shock to the dog whenever it crosses the boundaries marked by the wires. The shock is just like static and will cause no harm to your dog. All it does is offer a small irritating ‘reminder' to keep your dogs from moving beyond their permitted areas.
Also before it emits the shock, it gives off high-frequency beeps to warn the dog. Whenever the dog hears the beeps it will be alerted to the fact that the shock would come if the warning is not heeded. This ensures that the pet will not have to be reminded physically as much as it will be by audio.
You should also mark the areas off limits by using visual aids such as flags, and other visual aids. As the dog gradually understands and respects the boundaries, it will no longer need these aids to avoid the areas altogether.
Warnings and Conclusions Some owners are not comfortable with the fact that mild static is used to remind their pets of their boundaries. However, it should be noted that it is non-harmful and is a great alternative to cooping up a pet within a dark and dingy cage beyond the dog's comfort. Also electronic fences do not protect your dog against robbers as cages do. Thieves have to work at a cage or a series of gates to get to your dog. Although it keeps your pets from going out too far from the home, it does not keep others away from coming into your home.
Lee Dobbins writes for http://fences.home-webzone.com/ where you can learn more about all aspects of fences for your home.
Article Source: http://EzineArticles.com/?expert=Lee_Dobbins
It effectively keeps the dogs within the owner's property and helps dogs learn to know their boundaries. They are trained by the system to automatically stay away from the boundaries of the home. Electronic dog fences have the added advantage of not taking up any property space. They are totally controlled by the dog's collar, and the predefined areas the dog is allowed to stay in.
The great thing about electronic fences is the fact that they can be programmed and wired to protect other areas of your home that are prone to the playful mischief of your energetic dogs. This way you can protect fish ponds, flowerbeds, gardens, and other sensitive areas.
But how do these things work? They are pretty simple, if you come to think of it. Here is a step by step guide to how electronic dog fences are set up and used.
Your Dog's Electronic Fence
1. Area Wiring – First of all, thin antenna wires are buried around the perimeter of the areas you want off limits to your dog. These wires are usually parallel to your picket or perimeter fences that surround your property. These wires are light, not bulky and are pretty easy to install.
They can even be secured in non soil areas by means of normal attachments easily found at any hardware store. Just make sure they are safe from the elements and are not an impediment to your surroundings. These wires can be installed beside your fish pond, other pet cages, and off-limit areas.
The wiring can also be installed inside your home. It should be installed in a way that it does not become cumbersome. It can be laid out like normal cable wire. Just make sure it is secured to the walls or to stable furniture and is beyond the reach of toddlers or your pets. You could even put it under you rug or under your carpet.
2. Pet Collar – Your pet then is made to wear a special collar that can receive signals from the wires you just installed. It is this collar that acts as the fence. Your pet should be wearing the collar for the system to work. Without the collar, the electronic fence will uselessly benign.
The collar works using radio frequency and has a specially installed radio receiver to pick up signals from the antenna wires in your territory.
3. Train Your Dog – the systems sets off a very mild and harmless shock to the dog whenever it crosses the boundaries marked by the wires. The shock is just like static and will cause no harm to your dog. All it does is offer a small irritating ‘reminder' to keep your dogs from moving beyond their permitted areas.
Also before it emits the shock, it gives off high-frequency beeps to warn the dog. Whenever the dog hears the beeps it will be alerted to the fact that the shock would come if the warning is not heeded. This ensures that the pet will not have to be reminded physically as much as it will be by audio.
You should also mark the areas off limits by using visual aids such as flags, and other visual aids. As the dog gradually understands and respects the boundaries, it will no longer need these aids to avoid the areas altogether.
Warnings and Conclusions Some owners are not comfortable with the fact that mild static is used to remind their pets of their boundaries. However, it should be noted that it is non-harmful and is a great alternative to cooping up a pet within a dark and dingy cage beyond the dog's comfort. Also electronic fences do not protect your dog against robbers as cages do. Thieves have to work at a cage or a series of gates to get to your dog. Although it keeps your pets from going out too far from the home, it does not keep others away from coming into your home.
Lee Dobbins writes for http://fences.home-webzone.com/ where you can learn more about all aspects of fences for your home.
Article Source: http://EzineArticles.com/?expert=Lee_Dobbins
Electronic Dog Training Collar
Using an electronic dog training collar is the fastest and most humane way to train your dog. If you really love your dog and want to teach the basic obedience that will keep it safe then an electronic dog collar is the answer. Professional dog trainers especially those who train working dogs almost always employ an electronic dog training collar within their training program. Only village idiots and people who have no experience with electronic dog collars feel they are cruel to the dog. That being said if you have not seen the results of properly used quality electronic dog collar on a dog then you will find it hard to realize how fast a dog will learn.
The first thing you need to understand is that electronic dog training collars are part of any valid training program. They are not used just for correcting dogs with bad habits or behavior. A good dog trainer will use an electronic dog collar on any dog no matter what its demeanor or mentality. Many times we trainers describe dogs as being soft or hard and as such so of us are reluctant to use an electronic dog collar on a so called soft dog. Proper correction and stimulation levels will provide training communication that will benefit any dog. The electronic dog training collar will do the job that no other dog training tool can accomplish.
An electronic dog training collar provides positive enforcement or punishment. A dog that has a problem attacking snakes including rattlesnakes will learn eventually that it will be injured or in some cases die as a result of its behavior. However it is much more humane if you place an electronic dog collar on the dog and the next time he begins to worry a snake he receives a jolt of stimulation. He very quickly learns that attacking snakes will result in a very bad experience. Best of all he does not associate the experience with the trainer or handler. He sees the snake as the cause of his discomfort. Next time no yelling or calling the dog is necessary when you hear a rattler announcing his presence nearby. In addition even if the handler is not present the dog wants nothing to do with any snake. This is avoidance training ends the unwanted behavior for good. The electronic dog training collar saves another dogs life.
James Kesel, MS is the publisher of Career in Dog Training website. Providing information on various careers and methods in dog training. The use of an electronic dog training collar is the most humane and effective tool for avoidance training available. Despite what many uneducated people have stated a proplerly used electronic dog training collar does not harm the dog in any way.
Article Source: http://EzineArticles.com/?expert=Jim_Kesel
The first thing you need to understand is that electronic dog training collars are part of any valid training program. They are not used just for correcting dogs with bad habits or behavior. A good dog trainer will use an electronic dog collar on any dog no matter what its demeanor or mentality. Many times we trainers describe dogs as being soft or hard and as such so of us are reluctant to use an electronic dog collar on a so called soft dog. Proper correction and stimulation levels will provide training communication that will benefit any dog. The electronic dog training collar will do the job that no other dog training tool can accomplish.
An electronic dog training collar provides positive enforcement or punishment. A dog that has a problem attacking snakes including rattlesnakes will learn eventually that it will be injured or in some cases die as a result of its behavior. However it is much more humane if you place an electronic dog collar on the dog and the next time he begins to worry a snake he receives a jolt of stimulation. He very quickly learns that attacking snakes will result in a very bad experience. Best of all he does not associate the experience with the trainer or handler. He sees the snake as the cause of his discomfort. Next time no yelling or calling the dog is necessary when you hear a rattler announcing his presence nearby. In addition even if the handler is not present the dog wants nothing to do with any snake. This is avoidance training ends the unwanted behavior for good. The electronic dog training collar saves another dogs life.
James Kesel, MS is the publisher of Career in Dog Training website. Providing information on various careers and methods in dog training. The use of an electronic dog training collar is the most humane and effective tool for avoidance training available. Despite what many uneducated people have stated a proplerly used electronic dog training collar does not harm the dog in any way.
Article Source: http://EzineArticles.com/?expert=Jim_Kesel
Do Computers Get Tired?
A Silver Bullet?
Until recently, I would have dismissed the notion that electronic gunk can accumulate in a machine and cause it to act erratically. But a few months ago my high-speed Internet connection, which is normally rock solid, started getting flaky. I unplugged my cable modem, plugged it back in and voila... things were back to normal.
And since then I've repeated the procedure a few times with good results, whenever I noticed a slowdown in my Internet speed. So I started thinking... maybe electronic devices and appliances really do get tired, clogged with electrons, or whatever. It turns out that there is some good science to support this layman's observation.
Jerrold Foutz is a Scientist with a capital S. There aren't many people alive who know more about how electronic gadgets (especially power supplies) are supposed to work. So you might be surprised to hear that when your computer, microwave, VCR or high-tech coffee pot isn't behaving, his best advice is "just unplug it."
Totally Cosmic, Dude.In a fascinating article on electronics trouble shooting, Foutz talks about something called a Single Event Upset (SEU) that can cause electronic circuitry to malfunction. An SEU can be caused by a power glitch, or a cosmic ray passing through a integrated circuit, and can actually flip the logic state (from 1 to 0 or vice versa) of a circuit. A cascading effect may trigger a hardware lockup or an infinite loop in software.
For lots more technical details, and even some suggestions on how better design can help to prevent this problem, see the full article on Trouble Shooting Electronics.
Of course in the case of computers running complex operating system and application software, other factors may come into play. Sloppy coding practices can result in 'memory leaks' which over time will cause performance to degrade. But from the end user perspective, the problem looks no different than a hardware error caused by cosmic rays.
Fortunately, the solution is the same in both cases: shut it down, turn it back on, and things will be good again... for a while.
Reprinted from: http://www.askbobrankin.com/do_computers_get_tired.html
BOB RANKIN... is a tech writer and computer programmer who enjoys exploring the Internet and sharing the fruit of his experience with others. His work has appeared in ComputerWorld, NetGuide, and NY Newsday. Bob is publisher of the Internet TOURBUS newsletter, author of several computer books, and creator of the http://LowfatLinux.com website. Visit Bob Rankin's website for more helpful articles and free tech support.
Article Source: http://EzineArticles.com/?expert=Bob_Rankin
Until recently, I would have dismissed the notion that electronic gunk can accumulate in a machine and cause it to act erratically. But a few months ago my high-speed Internet connection, which is normally rock solid, started getting flaky. I unplugged my cable modem, plugged it back in and voila... things were back to normal.
And since then I've repeated the procedure a few times with good results, whenever I noticed a slowdown in my Internet speed. So I started thinking... maybe electronic devices and appliances really do get tired, clogged with electrons, or whatever. It turns out that there is some good science to support this layman's observation.
Jerrold Foutz is a Scientist with a capital S. There aren't many people alive who know more about how electronic gadgets (especially power supplies) are supposed to work. So you might be surprised to hear that when your computer, microwave, VCR or high-tech coffee pot isn't behaving, his best advice is "just unplug it."
Totally Cosmic, Dude.In a fascinating article on electronics trouble shooting, Foutz talks about something called a Single Event Upset (SEU) that can cause electronic circuitry to malfunction. An SEU can be caused by a power glitch, or a cosmic ray passing through a integrated circuit, and can actually flip the logic state (from 1 to 0 or vice versa) of a circuit. A cascading effect may trigger a hardware lockup or an infinite loop in software.
For lots more technical details, and even some suggestions on how better design can help to prevent this problem, see the full article on Trouble Shooting Electronics.
Of course in the case of computers running complex operating system and application software, other factors may come into play. Sloppy coding practices can result in 'memory leaks' which over time will cause performance to degrade. But from the end user perspective, the problem looks no different than a hardware error caused by cosmic rays.
Fortunately, the solution is the same in both cases: shut it down, turn it back on, and things will be good again... for a while.
Reprinted from: http://www.askbobrankin.com/do_computers_get_tired.html
BOB RANKIN... is a tech writer and computer programmer who enjoys exploring the Internet and sharing the fruit of his experience with others. His work has appeared in ComputerWorld, NetGuide, and NY Newsday. Bob is publisher of the Internet TOURBUS newsletter, author of several computer books, and creator of the http://LowfatLinux.com website. Visit Bob Rankin's website for more helpful articles and free tech support.
Article Source: http://EzineArticles.com/?expert=Bob_Rankin
Electronic Billiards Scoreboards
At competitive levels of billiards, a scoreboard is essential for displaying the scores of each player. Electronic billiards scoreboards are the latest trend for displaying the scores in billiards. It is a fast, easy, and reliable way of displaying how much time the player has left for the shot or for pre-match warming up. The commendable feature of electronic billiards scoreboards is the accuracy of the displayed information.
Electronic billiards scoreboards have a housing comprising a scorekeeping display adapted for billiards. Digits are generally composed of seven-segment displays, large dot-matrix made of LEDs, incandescent bulbs, or other electromechanical flip segments. The display can add or subtract from scores automatically. There is a power switch for activating and deactivating the scoreboard display.
Electronic billiards scoreboards are mounted on the wall as they are the focal point throughout tournaments for players as well as viewers. The scorekeeping display gives you information such as player statistics, updated scores, average time, average score, winning percentage, important tournament information, and sponsor messages. It also gives information about the current game, and a list of all played games.
Most of these scoreboards come with voice announcer, game clock, control box, wall mounting devices, and laser sound effects. Automatic player change and handicapping options are other advantages. For accuracy and reliability, some of them use infrared puck sensors. Fixed and portable electronic billiards scoreboards are available. There are many companies that manufacture and sell the best scoreboard devices. Most companies offer warranties for their product. Online shopping is an ideal alternative to get quality electronic billiards scoreboards.
Billiards provides detailed information on Billiards, History of Billiards, Rules of Billiards, Billiards Supplies and more. Billiards is affiliated with Pool Tables for Sale .
Article Source: http://EzineArticles.com/?expert=Eddie_Tobey
Electronic billiards scoreboards have a housing comprising a scorekeeping display adapted for billiards. Digits are generally composed of seven-segment displays, large dot-matrix made of LEDs, incandescent bulbs, or other electromechanical flip segments. The display can add or subtract from scores automatically. There is a power switch for activating and deactivating the scoreboard display.
Electronic billiards scoreboards are mounted on the wall as they are the focal point throughout tournaments for players as well as viewers. The scorekeeping display gives you information such as player statistics, updated scores, average time, average score, winning percentage, important tournament information, and sponsor messages. It also gives information about the current game, and a list of all played games.
Most of these scoreboards come with voice announcer, game clock, control box, wall mounting devices, and laser sound effects. Automatic player change and handicapping options are other advantages. For accuracy and reliability, some of them use infrared puck sensors. Fixed and portable electronic billiards scoreboards are available. There are many companies that manufacture and sell the best scoreboard devices. Most companies offer warranties for their product. Online shopping is an ideal alternative to get quality electronic billiards scoreboards.
Billiards provides detailed information on Billiards, History of Billiards, Rules of Billiards, Billiards Supplies and more. Billiards is affiliated with Pool Tables for Sale .
Article Source: http://EzineArticles.com/?expert=Eddie_Tobey
Friday, September 21, 2007
Antenna directivity and gain
Antennas (aerials) do not radiate equally in all directions. It is found that all realisable radio antennas radiate more in some directions than others. The actual pattern is dependent upon the type of antenna, its size, the environment and a variety of other factors.This directional pattern can be used to ensure that the power radiated is radiated in the desired directions.
It is normal to refer to the directional patterns and gain in terms of the transmitted signal. It is often easier to visualise the antenna is terms of its radiated power, however the antenna performs in an exactly equivalent manner for reception, having identical figures and specifications.
In order to visualise the way in which an antenna radiates a diagram known as a polar diagram is used. This is normally a two dimensional plot around an antenna showing the intensity of the radiation at each point for a particular plane. Normally the scale that is used is logarithmic so that the differences can be conveniently seen on the plot. Although the radiation pattern of the antenna varies in three dimensions, it is normal to make a plot in a particular plane, normally either horizontal or vertical as these are the two that are most used, and it simplifies the measurements and presentation. An example for a simple dipole antenna is shown below.
Polar diagram of a half wave dipole in free space
Antennas are often categorised by the type of polar diagram they exhibit. For example an omni-directional antenna is one which radiates equally (or approximately equally) in all directions in the plane of interest. An antenna that radiates equally in all directions in all planes is called an isotropic antenna. As already mentioned it is not possible to produce one of these in reality, but it is useful as a theoretical reference for some measurements. Other antennas exhibit highly directional patterns and these may be utilised in a number of applications. The Yagi antenna is an example of a directive antenna and possibly it is most widely used for television reception.
Polar diagram for a yagi antenna
There are a number of key features that can be seen from this polar diagram. The first is that there is a main beam or lobe and a number of minor lobes. It is often useful to define the beam-width of an antenna. This is taken to be angle between the two points where the power falls to half its maximum level, and as a result it is sometimes called the half power beam-width.
Antenna gain
An antenna radiates a given amount of power. This is the power dissipated in the radiation resistance of the antenna. An isotropic radiator will distribute this equally in all directions. For an antenna with a directional pattern, less power will be radiated in some directions and more in others. The fact that more power is radiated in given directions implies that it can be considered to have a gain.
The gain can be defined as a ratio of the signal transmitted in the "maximum" direction to that of a standard or reference antenna. This may sometimes be called the "forward gain". The figure that is obtained is then normally expressed in decibels (dB). In theory the standard antenna could be almost anything but two types are generally used. The most common type is a simple dipole as it is easily available and it is the basis of many other types of antenna. In this case the gain is often expressed as dBd i.e. gain expressed in decibels over a dipole. However a dipole does not radiated equally in all directions in all planes and so an isotropic source is sometimes used. In this case the gain may be specified in dBi i.e. gain in decibels over an isotropic source. The main drawback with using an isotropic source as a reference is that it is not possible to realise them in practice and so that figures using it can only be theoretical. However it is possible to relate the two gains as a dipole has a gain of 2.1 dB over an isotropic source i.e. 2.1 dBi. In other words, figures expressed as gain over an isotropic source will be 2.1 dB higher than those relative to a dipole. When choosing an antenna and looking at the gain specifications, be sure to check whether the gain is relative to a dipole or an isotropic source.
Apart from the forward gain of an antenna another parameter which is important is the front to back ratio. This is expressed in decibels and as the name implies it is the ratio of the maximum signal in the forward direction to the signal in the opposite direction. This figure is normally expressed in decibels. It is found that the design of an antenna can be adjusted to give either maximum forward gain of the optimum front to back ratio as the two do not normally coincide exactly. For most VHF and UHF operation the design is normally optimised for the optimum forward gain as this gives the maximum radiated signal in the required direction.
Gain / beamwidth balance
It may appear that maximising the gain of an antenna will optimise its performance in a system. This may not always be the case. By the very nature of gain and beamwidth, increasing the gain will result in a reduction in the beamwidth. This will make setting the direction of the antenna more critical. This may be quite acceptable in many applications, but not in others. This balance should be considered when designing and setting up a radio link.
http://kazus.info/articles/5.html
It is normal to refer to the directional patterns and gain in terms of the transmitted signal. It is often easier to visualise the antenna is terms of its radiated power, however the antenna performs in an exactly equivalent manner for reception, having identical figures and specifications.
In order to visualise the way in which an antenna radiates a diagram known as a polar diagram is used. This is normally a two dimensional plot around an antenna showing the intensity of the radiation at each point for a particular plane. Normally the scale that is used is logarithmic so that the differences can be conveniently seen on the plot. Although the radiation pattern of the antenna varies in three dimensions, it is normal to make a plot in a particular plane, normally either horizontal or vertical as these are the two that are most used, and it simplifies the measurements and presentation. An example for a simple dipole antenna is shown below.
Polar diagram of a half wave dipole in free space
Antennas are often categorised by the type of polar diagram they exhibit. For example an omni-directional antenna is one which radiates equally (or approximately equally) in all directions in the plane of interest. An antenna that radiates equally in all directions in all planes is called an isotropic antenna. As already mentioned it is not possible to produce one of these in reality, but it is useful as a theoretical reference for some measurements. Other antennas exhibit highly directional patterns and these may be utilised in a number of applications. The Yagi antenna is an example of a directive antenna and possibly it is most widely used for television reception.
Polar diagram for a yagi antenna
There are a number of key features that can be seen from this polar diagram. The first is that there is a main beam or lobe and a number of minor lobes. It is often useful to define the beam-width of an antenna. This is taken to be angle between the two points where the power falls to half its maximum level, and as a result it is sometimes called the half power beam-width.
Antenna gain
An antenna radiates a given amount of power. This is the power dissipated in the radiation resistance of the antenna. An isotropic radiator will distribute this equally in all directions. For an antenna with a directional pattern, less power will be radiated in some directions and more in others. The fact that more power is radiated in given directions implies that it can be considered to have a gain.
The gain can be defined as a ratio of the signal transmitted in the "maximum" direction to that of a standard or reference antenna. This may sometimes be called the "forward gain". The figure that is obtained is then normally expressed in decibels (dB). In theory the standard antenna could be almost anything but two types are generally used. The most common type is a simple dipole as it is easily available and it is the basis of many other types of antenna. In this case the gain is often expressed as dBd i.e. gain expressed in decibels over a dipole. However a dipole does not radiated equally in all directions in all planes and so an isotropic source is sometimes used. In this case the gain may be specified in dBi i.e. gain in decibels over an isotropic source. The main drawback with using an isotropic source as a reference is that it is not possible to realise them in practice and so that figures using it can only be theoretical. However it is possible to relate the two gains as a dipole has a gain of 2.1 dB over an isotropic source i.e. 2.1 dBi. In other words, figures expressed as gain over an isotropic source will be 2.1 dB higher than those relative to a dipole. When choosing an antenna and looking at the gain specifications, be sure to check whether the gain is relative to a dipole or an isotropic source.
Apart from the forward gain of an antenna another parameter which is important is the front to back ratio. This is expressed in decibels and as the name implies it is the ratio of the maximum signal in the forward direction to the signal in the opposite direction. This figure is normally expressed in decibels. It is found that the design of an antenna can be adjusted to give either maximum forward gain of the optimum front to back ratio as the two do not normally coincide exactly. For most VHF and UHF operation the design is normally optimised for the optimum forward gain as this gives the maximum radiated signal in the required direction.
Gain / beamwidth balance
It may appear that maximising the gain of an antenna will optimise its performance in a system. This may not always be the case. By the very nature of gain and beamwidth, increasing the gain will result in a reduction in the beamwidth. This will make setting the direction of the antenna more critical. This may be quite acceptable in many applications, but not in others. This balance should be considered when designing and setting up a radio link.
http://kazus.info/articles/5.html
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