Antenna_(radio)

qas: question: What device is able to change electric powerinto radio waves and also do the reverse?
answers: text: An antenna

question: What device is often used in conjuntion with the antenna?
answers: text: radio transmitter or radio receiver

question: What process associated with antennas produces a high frequency alternating current?
answers: text: transmission

question: What else can radio waves be called?
answers: text: electromagnetic waves

question: When does an antenna catch electromagnetic waves?
answers: text: reception
context: An antenna (plural antennae or antennas), or aerial, is an electrical device which converts electric power into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter supplies an electric current oscillating at radio frequency (i.e. a high frequency alternating current (AC)) to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified.

qas: question: What is frequently used to connect elements to the receiver?
answers: text: transmission line

question: What particles are pushed through the antenna by a transmitter?
answers: text: electrons

question: During transmission does the electric field wave move closer to the antenna?
answers: text: radiate away

question: During what process would electrons be vacillating in the antenna?
answers: text: reception
context: Typically an antenna consists of an arrangement of metallic conductors (elements), electrically connected (often through a transmission line) to the receiver or transmitter. An oscillating current of electrons forced through the antenna by a transmitter will create an oscillating magnetic field around the antenna elements, while the charge of the electrons also creates an oscillating electric field along the elements. These time-varying fields radiate away from the antenna into space as a moving transverse electromagnetic field wave. Conversely, during reception, the oscillating electric and magnetic fields of an incoming radio wave exert force on the electrons in the antenna elements, causing them to move back and forth, creating oscillating currents in the antenna.

qas: question: What is an acceptable synonym for antenna?
answers: text: aerial

question: What can sometimes be meant by the term aerial specifically?
answers: text: wire antenna

question: What is one way of referring to more than one antenna?
answers: text: antennae

question: What is the most widely accepted term for an electrical device that converts electric power into radio waves?
answers: text: antenna
context: The words antenna (plural: antennas in US English, although both "antennas" and "antennae" are used in International English) and aerial are used interchangeably. Occasionally the term "aerial" is used to mean a wire antenna. However, note the important international technical journal, the IEEE Transactions on Antennas and Propagation. In the United Kingdom and other areas where British English is used, the term aerial is sometimes used although 'antenna' has been universal in professional use for many years.

qas: question: Who is most associated with the emergence of the word antenna?
answers: text: Guglielmo Marconi

question: When did experimentation with electromagnetic waves begin?
answers: text: 1895

question: What is a way to increase the strength of a radio transmission?
answers: text: raising the "aerial" wire

question: How far was Marconi able to get his signal to go using this technique?
answers: text: 1.5 mi
context: The origin of the word antenna relative to wireless apparatus is attributed to Italian radio pioneer Guglielmo Marconi. In the summer of 1895, Marconi began testing his wireless system outdoors on his father's estate near Bologna and soon began to experiment with long wire "aerials". Marconi discovered that by raising the "aerial" wire above the ground and connecting the other side of his transmitter to ground, the transmission range was increased. Soon he was able to transmit signals over a hill, a distance of approximately 2.4 kilometres (1.5 mi). In Italian a tent pole is known as l'antenna centrale, and the pole with the wire was simply called l'antenna. Until then wireless radiating transmitting and receiving elements were known simply as aerials or terminals.

qas: question: What is essential for the mating of the elements that create radio waves?
answers: text: Antennas

question: How fast are signals produced by antenna transmitted?
answers: text: speed of light

question: What is one system that uses electromagnetic waves?
answers: text: mobile telephones

question: What mobile locator and direction finder technology takes advantage of radio waves?
answers: text: GPS

question: What often inconspicuous part of a laptop computer allows for internet usage?
answers: text: antennas
context: Antennas are required by any radio receiver or transmitter to couple its electrical connection to the electromagnetic field. Radio waves are electromagnetic waves which carry signals through the air (or through space) at the speed of light with almost no transmission loss. Radio transmitters and receivers are used to convey signals (information) in systems including broadcast (audio) radio, television, mobile telephones, Wi-Fi (WLAN) data networks, trunk lines and point-to-point communications links (telephone, data networks), satellite links, many remote controlled devices such as garage door openers, and wireless remote sensors, among many others. Radio waves are also used directly for measurements in technologies including radar, GPS, and radio astronomy. In each and every case, the transmitters and receivers involved require antennas, although these are sometimes hidden (such as the antenna inside an AM radio or inside a laptop computer equipped with Wi-Fi).

qas: question: What is the main element of an omnidirectional antenna?
answers: text: metal rod

question: What type of antenna would most likely be a half a wavelength long?
answers: text: dipole

question: In which direction would you expect to find a dipole?
answers: text: horizontally

question: What is meant by the area where signals cannot be accepted well along the conductor?
answers: text: null
context: One example of omnidirectional antennas is the very common vertical antenna or whip antenna consisting of a metal rod (often, but not always, a quarter of a wavelength long). A dipole antenna is similar but consists of two such conductors extending in opposite directions, with a total length that is often, but not always, a half of a wavelength long. Dipoles are typically oriented horizontally in which case they are weakly directional: signals are reasonably well radiated toward or received from all directions with the exception of the direction along the conductor itself; this region is called the antenna blind cone or null.

qas: question: Are basic antennas expensive?
answers: text: relatively inexpensive

question: What is the foundation most often used when creating new antenna models?
answers: text: dipole antenna

question: What category do vertical antennas fall under?
answers: text: monopole antenna

question: What is used to close the circuit of a dipole antenna?
answers: text: large conductive surface
context: Both the vertical and dipole antennas are simple in construction and relatively inexpensive. The dipole antenna, which is the basis for most antenna designs, is a balanced component, with equal but opposite voltages and currents applied at its two terminals through a balanced transmission line (or to a coaxial transmission line through a so-called balun). The vertical antenna, on the other hand, is a monopole antenna. It is typically connected to the inner conductor of a coaxial transmission line (or a matching network); the shield of the transmission line is connected to ground. In this way, the ground (or any large conductive surface) plays the role of the second conductor of a dipole, thereby forming a complete circuit. Since monopole antennas rely on a conductive ground, a so-called grounding structure may be employed to provide a better ground contact to the earth or which itself acts as a ground plane to perform that function regardless of (or in absence of) an actual contact with the earth.

qas: question: What are different designs aimed at increasing?
answers: text: gain of the antenna

question: What is different from a monopole antenna with most other antenna types?
answers: text: balanced line

question: Gain when referring to an antenna refers to what about radiated power?
answers: text: concentration

question: Where is the power that is distributed originating from?
answers: text: the transmitter
context: Antennas more complex than the dipole or vertical designs are usually intended to increase the directivity and consequently the gain of the antenna. This can be accomplished in many different ways leading to a plethora of antenna designs. The vast majority of designs are fed with a balanced line (unlike a monopole antenna) and are based on the dipole antenna with additional components (or elements) which increase its directionality. Antenna "gain" in this instance describes the concentration of radiated power into a particular solid angle of space, as opposed to the spherically uniform radiation of the ideal radiator. The increased power in the desired direction is at the expense of that in the undesired directions. Power is conserved, and there is no net power increase over that delivered from the power source (the transmitter.)

qas: question: How many antenna would make up a phased array?
answers: text: two or more

question: How are antennas oriented when arranged with specific spacing?
answers: text: parallel

question: What are the two standard antenna types?
answers: text: omnidirectional or weakly directional

question: What determines if the antenna creates a broadside array or an end fire array?
answers: text: relative phase
context: For instance, a phased array consists of two or more simple antennas which are connected together through an electrical network. This often involves a number of parallel dipole antennas with a certain spacing. Depending on the relative phase introduced by the network, the same combination of dipole antennas can operate as a "broadside array" (directional normal to a line connecting the elements) or as an "end-fire array" (directional along the line connecting the elements). Antenna arrays may employ any basic (omnidirectional or weakly directional) antenna type, such as dipole, loop or slot antennas. These elements are often identical.

qas: question: What type of antenna formation is made up of multiple dipole elements of varying lengths?
answers: text: log-periodic dipole array

question: What is the benefit of this formation type?
answers: text: extremely wide bandwidth

question: What is the main application of these set ups?
answers: text: television reception

question: What is a variation of this antenna type?
answers: text: Yagi-Uda Antenna
context: However a log-periodic dipole array consists of a number of dipole elements of different lengths in order to obtain a somewhat directional antenna having an extremely wide bandwidth: these are frequently used for television reception in fringe areas. The dipole antennas composing it are all considered "active elements" since they are all electrically connected together (and to the transmission line). On the other hand, a superficially similar dipole array, the Yagi-Uda Antenna (or simply "Yagi"), has only one dipole element with an electrical connection; the other so-called parasitic elements interact with the electromagnetic field in order to realize a fairly directional antenna but one which is limited to a rather narrow bandwidth. The Yagi antenna has similar looking parasitic dipole elements but which act differently due to their somewhat different lengths. There may be a number of so-called "directors" in front of the active element in the direction of propagation, and usually a single (but possibly more) "reflector" on the opposite side of the active element.

qas: question: For radio broadcast that one would hear in their car what type of towers are used?
answers: text: vertical

question: Why is this specific antenna type used?
answers: text: achieve directionality

question: If one wished to take an antenna to different locations, which type would be best?
answers: text: short vertical antenna

question: What is a problem one might encounter when using a portable antenna?
answers: text: impedance matching
context: At low frequencies (such as AM broadcast), arrays of vertical towers are used to achieve directionality  and they will occupy large areas of land. For reception, a long Beverage antenna can have significant directivity. For non directional portable use, a short vertical antenna or small loop antenna works well, with the main design challenge being that of impedance matching. With a vertical antenna a loading coil at the base of the antenna may be employed to cancel the reactive component of impedance; small loop antennas are tuned with parallel capacitors for this purpose.

qas: question: What is mainly responsible for the connection of the antenna to its end destinations?
answers: text: antenna lead-in

question: What is the group of elements used to join the elements of an antenna?
answers: text: antenna feed

question: What are the type of antennas used with satellite television called?
answers: text: aperture antenna

question: What can be used in place of  a standard transmission line?
answers: text: microwave antenna
context: An antenna lead-in is the transmission line (or feed line) which connects the antenna to a transmitter or receiver. The antenna feed may refer to all components connecting the antenna to the transmitter or receiver, such as an impedance matching network in addition to the transmission line. In a so-called aperture antenna, such as a horn or parabolic dish, the "feed" may also refer to a basic antenna inside the entire system (normally at the focus of the parabolic dish or at the throat of a horn) which could be considered the one active element in that antenna system. A microwave antenna may also be fed directly from a waveguide in place of a (conductive) transmission line.

qas: question: Monopole antennas consist of what element?
answers: text: metal rod

question: What the most common form? 
answers: text: quarter-wave monopole

question: What are small monopoles used as?
answers: text: nondirectional antennas

question: What has vertical polarization?
answers: text: Monopoles
context: Monopole antennas consist of a single radiating element such as a metal rod, often mounted over a conducting surface, a ground plane. One side of the feedline from the receiver or transmitter is connected to the rod, and the other side to the ground plane, which may be the Earth. The most common form is the quarter-wave monopole which is one-quarter of a wavelength long and has a gain of 5.12 dBi when mounted over a ground plane. Monopoles have an omnidirectional radiation pattern, so they are used for broad coverage of an area, and have vertical polarization. The ground waves used for broadcasting at low frequencies must be vertically polarized, so large vertical monopole antennas are used for broadcasting in the MF, LF, and VLF bands. Small monopoles are used as nondirectional antennas on portable radios in the HF, VHF, and UHF bands.

qas: question: What is the most widley used antenna class?
answers: text: dipole antenna

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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         What radiates two lobes perpendicular to the antennas axis?                                                                                                                                       
answers: text: horizontal dipole

question: Besides low gain antennas, what is also used as driven elements in complicated higher gain types of antennas?
answers: text: dipoles

question: How much gain does a half-wave dipole have?
answers: text: 2.15 dBi
context: The most widely used class of antenna, a dipole antenna consists of two symmetrical radiators such as metal rods or wires, with one side of the balanced feedline from the transmitter or receiver attached to each. A horizontal dipole radiates in two lobes perpendicular to the antenna's axis. A half-wave dipole the most common type, has two collinear elements each a quarter wavelength long and a gain of 2.15 dBi. Used individually as low gain antennas, dipoles are also used as driven elements in many more complicated higher gain types of antennas.

qas: question: What must be true of the antenna and transmission medium for the repiprocity rule to apply ?
answers: text: linear and reciprocal

question: What is called when the direction of the elctrical current does not make a difference to the current?
answers: text: Reciprocal

question: What is one material that does not have this quality?
answers: text: ferrite

question: How can the lack of this quality be used in an everyday way?
answers: text: radar
context: A necessary condition for the aforementioned reciprocity property is that the materials in the antenna and transmission medium are linear and reciprocal. Reciprocal (or bilateral) means that the material has the same response to an electric current or magnetic field in one direction, as it has to the field or current in the opposite direction. Most materials used in antennas meet these conditions, but some microwave antennas use high-tech components such as isolators and circulators, made of nonreciprocal materials such as ferrite. These can be used to give the antenna a different behavior on receiving than it has on transmitting, which can be useful in applications like radar.

qas: question: How could one deide what type of antenna is nedded for a project?
answers: text: performance measures

question: What would most likely be the main concern in making this decision?
answers: text: directional characteristics

question: How would you distribute power to allow for a greater gain?
answers: text: horizontal directions

question: What is often the most imprtant crediting factor of antennas?
answers: text: efficiency
context: Antennas are characterized by a number of performance measures which a user would be concerned with in selecting or designing an antenna for a particular application. Chief among these relate to the directional characteristics (as depicted in the antenna's radiation pattern) and the resulting gain. Even in omnidirectional (or weakly directional) antennas, the gain can often be increased by concentrating more of its power in the horizontal directions, sacrificing power radiated toward the sky and ground. The antenna's power gain (or simply "gain") also takes into account the antenna's efficiency, and is often the primary figure of merit.

qas: question: Which antenna type would be best for a project requiring a specific frequency?
answers: text: Resonant antennas

question: How could an antenna be made to coordinate with the needed frequency?
answers: text: built or ordered

question: What factor would result in a desired feedback independence?
answers: text: particular antenna design

question: If you were unable to choose the antenna you wanted how could you still achieve this result?
answers: text: matching network
context: Resonant antennas are expected to be used around a particular resonant frequency; an antenna must therefore be built or ordered to match the frequency range of the intended application. A particular antenna design will present a particular feedpoint impedance. While this may affect the choice of an antenna, an antenna's impedance can also be adapted to the desired impedance level of a system using a matching network while maintaining the other characteristics (except for a possible loss of efficiency).

qas: question: What is the essential difference in radio waves transmitted by an antenna?
answers: text: polarization

question: How can this be adjusted more easily than changing antenna types?
answers: text: tilting the axis

question: When might the size of an antenna cause an issue?
answers: text: at lower frequencies

question: There is a relationship between the size of the antenna and the size of the wavelength with what antenna type?
answers: text: Highly directional

question: What size antenna would not be good when the antenna needs to be directional?
answers: text: small
context: An antenna transmits and receives radio waves with a particular polarization which can be reoriented by tilting the axis of the antenna in many (but not all) cases. The physical size of an antenna is often a practical issue, particularly at lower frequencies (longer wavelengths). Highly directional antennas need to be significantly larger than the wavelength. Resonant antennas usually use a linear conductor (or element), or pair of such elements, each of which is about a quarter of the wavelength in length (an odd multiple of quarter wavelengths will also be resonant). Antennas that are required to be small compared to the wavelength sacrifice efficiency and cannot be very directional. Fortunately at higher frequencies (UHF, microwaves) trading off performance to obtain a smaller physical size is usually not required.

qas: question: What is the basis for the way most antennas are developed?
answers: text: resonance principle

question: What particle's migration does the resonance principle rely on?
answers: text: electrons

question: What type of surface is formed by the tip of a conductor?
answers: text: reflective

question: How would you place the conductor in relation to the signal you wished to obtain?
answers: text: perpendicular
context: The majority of antenna designs are based on the resonance principle. This relies on the behaviour of moving electrons, which reflect off surfaces where the dielectric constant changes, in a fashion similar to the way light reflects when optical properties change. In these designs, the reflective surface is created by the end of a conductor, normally a thin metal wire or rod, which in the simplest case has a feed point at one end where it is connected to a transmission line. The conductor, or element, is aligned with the electrical field of the desired signal, normally meaning it is perpendicular to the line from the antenna to the source (or receiver in the case of a broadcast antenna).

qas: question: What part of the radio signal creates voltage?
answers: text: electrical component

question: What would the electric current always gravitate to?
answers: text: instantaneous field

question: What is the outcome when a curren is reflected>
answers: text: 180 degree change in phase

question: What amount of phase change would return a signal to its originial state?
answers: text: 360 degree
context: The radio signal's electrical component induces a voltage in the conductor. This causes an electrical current to begin flowing in the direction of the signal's instantaneous field. When the resulting current reaches the end of the conductor, it reflects, which is equivalent to a 180 degree change in phase. If the conductor is 1⁄4 of a wavelength long, current from the feed point will undergo 90 degree phase change by the time it reaches the end of the conductor, reflect through 180 degrees, and then another 90 degrees as it travels back. That means it has undergone a total 360 degree phase change, returning it to the original signal. The current in the element thus adds to the current being created from the source at that instant. This process creates a standing wave in the conductor, with the maximum current at the feed.

qas: question: What is the most popular antenna type?
answers: text: half-wave dipole

question: Elements in a half wave dipole and on an identical axis are said to be what?
answers: text: collinear

question: What is the current usually beng put into it or pulled out of?
answers: text: transmission line

question: What antenna type is a portion of the half wave dipole?
answers: text: Monopoles

question: What popular type combines more that one antenna?
answers: text: folded dipole
context: The ordinary half-wave dipole is probably the most widely used antenna design. This consists of two 1⁄4-wavelength elements arranged end-to-end, and lying along essentially the same axis (or collinear), each feeding one side of a two-conductor transmission wire. The physical arrangement of the two elements places them 180 degrees out of phase, which means that at any given instant one of the elements is driving current into the transmission line while the other is pulling it out. The monopole antenna is essentially one half of the half-wave dipole, a single 1⁄4-wavelength element with the other side connected to ground or an equivalent ground plane (or counterpoise). Monopoles, which are one-half the size of a dipole, are common for long-wavelength radio signals where a dipole would be impractically large. Another common design is the folded dipole, which is essentially two dipoles placed side-by-side and connected at their ends to make a single one-wavelength antenna.

qas: question: What frequency are antennas normally designed to be?
answers: text: f0

question: What can be added to f0 to create a standing wave pattern?
answers: text: 3f0

question: What multiple is essential for wavelengths?
answers: text: 1⁄4

question: How are waves which are used in the ways discussed controlled?
answers: text: harmonically
context: The standing wave forms with this desired pattern at the design frequency, f0, and antennas are normally designed to be this size. However, feeding that element with 3f0 (whose wavelength is 1⁄3 that of f0) will also lead to a standing wave pattern. Thus, an antenna element is also resonant when its length is 3⁄4 of a wavelength. This is true for all odd multiples of 1⁄4 wavelength. This allows some flexibility of design in terms of antenna lengths and feed points. Antennas used in such a fashion are known to be harmonically operated.

qas: question: How do quarter wave elements act in relation to a series relevant electrical element?
answers: text: imitate

question: What frequency develops a current peak?
answers: text: resonant frequency

question: How would you describe a current that has maximum efficiency?
answers: text: minimum reactance

question: What could be the best possible output versus input ratio?
answers: text: lossless
context: The quarter-wave elements imitate a series-resonant electrical element due to the standing wave present along the conductor. At the resonant frequency, the standing wave has a current peak and voltage node (minimum) at the feed. In electrical terms, this means the element has minimum reactance, generating the maximum current for minimum voltage. This is the ideal situation, because it produces the maximum output for the minimum input, producing the highest possible efficiency. Contrary to an ideal (lossless) series-resonant circuit, a finite resistance remains (corresponding to the relatively small voltage at the feed-point) due to the antenna's radiation resistance as well as any actual electrical losses.

qas: question: What could be coupled with an antenna to form pure resistance?
answers: text: inductance

question: What element would this pure resistance be coupled with?
answers: text: transmission line

question: What phrase describes the process of purposely using a lower standing antenna at a less than peak frequency?
answers: text: electrical lengthening
context: It is possible to use the impedance matching concepts to construct vertical antennas substantially shorter than the 1⁄4 wavelength at which the antenna is resonant. By adding an inductance in series with the antenna, a so-called loading coil, the capacitive reactance of this antenna can be cancelled leaving a pure resistance which can then be matched to the transmission line. Sometimes the resulting resonant frequency of such a system (antenna plus matching network) is described using the construct of electrical length and the use of a shorter antenna at a lower frequency than its resonant frequency is termed electrical lengthening.

qas: question:  If your were unable to match the source frequency with the design frequency of the antenna what could you use?
answers: text: resonant multiples

question: What is the most common application of resonant antennas?
answers: text: single target signal

question: What antenna setup type is generally used for TV viewing?
answers: text: resonant

question: For use with more than one channel changes are made to increase what property?
answers: text: bandwidth
context: The end result is that the resonant antenna will efficiently feed a signal into the transmission line only when the source signal's frequency is close to that of the design frequency of the antenna, or one of the resonant multiples. This makes resonant antenna designs inherently narrowband, and they are most commonly used with a single target signal. They are particularly common on radar systems, where the same antenna is used for both broadcast and reception, or for radio and television broadcasts, where the antenna is working with a single frequency. They are less commonly used for reception where multiple channels are present, in which case additional modifications are used to increase the bandwidth, or entirely different antenna designs are used.

qas: question: What accounts for the geometry involved in the use of an antenna?
answers: text: inverse square law

question:  How is the compactness of the signal measured?
answers: text: Watts per square metre

question: What type of project would call for more than one element used together?
answers: text: higher performance
context: The amount of signal received from a distant transmission source is essentially geometric in nature due to the inverse square law, and this leads to the concept of effective area. This measures the performance of an antenna by comparing the amount of power it generates to the amount of power in the original signal, measured in terms of the signal's power density in Watts per square metre. A half-wave dipole has an effective area of 0.13 2. If more performance is needed, one cannot simply make the antenna larger. Although this would intercept more energy from the signal, due to the considerations above, it would decrease the output significantly due to it moving away from the resonant length. In roles where higher performance is needed, designers often use multiple elements combined together.

qas: question: What is a half wave dipole need to be coupled with in most instances?
answers: text: feed point

question: What part of the current is usually strongest?
answers: text: center

question: What does this result in?
answers: text: standing wave pattern

question: Element used to provide support to the original signal are called?
answers: text: passive elements
context: Returning to the basic concept of current flows in a conductor, consider what happens if a half-wave dipole is not connected to a feed point, but instead shorted out. Electrically this forms a single 1⁄2-wavelength element. But the overall current pattern is the same; the current will be zero at the two ends, and reach a maximum in the center. Thus signals near the design frequency will continue to create a standing wave pattern. Any varying electrical current, like the standing wave in the element, will radiate a signal. In this case, aside from resistive losses in the element, the rebroadcast signal will be significantly similar to the original signal in both magnitude and shape. If this element is placed so its signal reaches the main dipole in-phase, it will reinforce the original signal, and increase the current in the dipole. Elements used in this way are known as passive elements.

qas: question: What can take advantage of these elements to add more gain?
answers: text: Yagi-Uda array

question: Does this device improve the operation of the antenna?
answers: text: does not contribute

question: What is the name for passive elements nearer to the source of the signal?
answers: text: directors

question: Adding more elements to a Yagi-Uda would have what effect?
answers: text: increasingly directional
context: A Yagi-Uda array uses passive elements to greatly increase gain. It is built along a support boom that is pointed toward the signal, and thus sees no induced signal and does not contribute to the antenna's operation. The end closer to the source is referred to as the front. Near the rear is a single active element, typically a half-wave dipole or folded dipole. Passive elements are arranged in front (directors) and behind (reflectors) the active element along the boom. The Yagi has the inherent quality that it becomes increasingly directional, and thus has higher gain, as the number of elements increases. However, this also makes it increasingly sensitive to changes in frequency; if the signal frequency changes, not only does the active element receive less energy directly, but all of the passive elements adding to that signal also decrease their output as well and their signals no longer reach the active element in-phase.

qas: question: What can be paired with transmission lines to create phases that would support output?
answers: text: active elements

question: What is the most common element used to create a single in phase signal?
answers: text: half-wave dipoles

question: What must be precise in order to create this signal at output?
answers: text: phase lengths

question: What is a more complicated occurrence of the single in-phase producing antenna?
answers: text: log-periodic
context: It is also possible to use multiple active elements and combine them together with transmission lines to produce a similar system where the phases add up to reinforce the output. The antenna array and very similar reflective array antenna consist of multiple elements, often half-wave dipoles, spaced out on a plane and wired together with transmission lines with specific phase lengths to produce a single in-phase signal at the output. The log-periodic antenna is a more complex design that uses multiple in-line elements similar in appearance to the Yagi-Uda but using transmission lines between the elements to produce the output.

qas: question: If you wanted to somehow clone the original signal you could use?
answers: text: extended conductive surface

question: What effect would the use of a reflector have on a signal?
answers: text: increase

question: What allowance can be made for gaps without loss of performance?
answers: text: less than 1⁄10

question: What is the most recognized type of an antenna that has its basis in reflection?
answers: text: parabolic reflector
context: Reflection of the original signal also occurs when it hits an extended conductive surface, in a fashion similar to a mirror. This effect can also be used to increase signal through the use of a reflector, normally placed behind the active element and spaced so the reflected signal reaches the element in-phase. Generally the reflector will remain highly reflective even if it is not solid; gaps less than 1⁄10 generally have little effect on the outcome. For this reason, reflectors often take the form of wire meshes or rows of passive elements, which makes them lighter and less subject to wind. The parabolic reflector is perhaps the best known example of a reflector-based antenna, which has an effective area far greater than the active element alone.

qas: question: What magnifies the small radiation resistance of a loop?
answers: text: a capacitor at the frequency of operation

question: What is used in most AM broadcaster receivers?
answers: text: loop

question: What is resonated by a capacitor along with the receiver tuning that maintains resonance over the AM broadcast band?
answers: text: small ferrite loop antenna

question: When using a small loop antenna at a low frequency, what may occur?
answers: text: impedance matching
context: Another extreme case of impedance matching occurs when using a small loop antenna (usually, but not always, for receiving) at a relatively low frequency where it appears almost as a pure inductor. Resonating such an inductor with a capacitor at the frequency of operation not only cancels the reactance but greatly magnifies the very small radiation resistance of such a loop.[citation needed] This is implemented in most AM broadcast receivers, with a small ferrite loop antenna resonated by a capacitor which is varied along with the receiver tuning in order to maintain resonance over the AM broadcast band

qas: question: Where does cancellation of any reactance seen?
answers: text: antenna terminals

question: What is left after antenna tuning?
answers: text: resistive impedance

question: What can be used to cancel a inductibe reactance or residual capacitative?
answers: text: parallel capacitance

question: What is an antenna designed to have?
answers: text: purely resistive feedpoint
context: Antenna tuning generally refers to cancellation of any reactance seen at the antenna terminals, leaving only a resistive impedance which might or might not be exactly the desired impedance (that of the transmission line). Although an antenna may be designed to have a purely resistive feedpoint impedance (such as a dipole 97% of a half wavelength long) this might not be exactly true at the frequency that it is eventually used at. In some cases the physical length of the antenna can be "trimmed" to obtain a pure resistance. On the other hand, the addition of a series inductance or parallel capacitance can be used to cancel a residual capacitative or inductive reactance, respectively.

qas: question: What type of antenna has impedance at a specific frequency?
answers: text: resonant

question: What term can be used to refer to the usable spectrum of an antennas frequency?
answers: text: bandwidth

question: What causes the frequencies outside of the bandwidth to be unusable?
answers: text: impedance match

question: What is lessened by the Yagi-Uda design?
answers: text: directivity
context: Although a resonant antenna has a purely resistive feed-point impedance at a particular frequency, many (if not most) applications require using an antenna over a range of frequencies. An antenna's bandwidth specifies the range of frequencies over which its performance does not suffer due to a poor impedance match. Also in the case of a Yagi-Uda array, the use of the antenna very far away from its design frequency reduces the antenna's directivity, thus reducing the usable bandwidth regardless of impedance matching.

qas: question: What characteristic would be better if it were steady?
answers: text: reactance

question: What characteristic of the conductor changes the amount of reactance?
answers: text: diameter

question: What would be used to create a half wave or quarter wave dipole?
answers: text: A long thin wire
context: Instead, it is often desired to have an antenna whose impedance does not vary so greatly over a certain bandwidth. It turns out that the amount of reactance seen at the terminals of a resonant antenna when the frequency is shifted, say, by 5%, depends very much on the diameter of the conductor used. A long thin wire used as a half-wave dipole (or quarter wave monopole) will have a reactance significantly greater than the resistive impedance it has at resonance, leading to a poor match and generally unacceptable performance. Making the element using a tube of a diameter perhaps 1/50 of its length, however, results in a reactance at this altered frequency which is not so great, and a much less serious mismatch which will only modestly damage the antenna's net performance. Thus rather thick tubes are typically used for the solid elements of such antennas, including Yagi-Uda arrays.

qas: question: What type of tubes are generally used for sturdier always of antennas?
answers: text: cages

question: What effect do cages have on the spectrum of usable frequencies?
answers: text: widens

question: How could one achieve the task of creating an antenna that can be Used over various bands?
answers: text: connecting resonant elements

question: What is an essential for dealing with directing the flow of power?
answers: text: trap's
context: Rather than just using a thick tube, there are similar techniques used to the same effect such as replacing thin wire elements with cages to simulate a thicker element. This widens the bandwidth of the resonance. On the other hand, amateur radio antennas need to operate over several bands which are widely separated from each other. This can often be accomplished simply by connecting resonant elements for the different bands in parallel. Most of the transmitter's power will flow into the resonant element while the others present a high (reactive) impedance and draw little current from the same voltage. A popular solution uses so-called traps consisting of parallel resonant circuits which are strategically placed in breaks along each antenna element. When used at one particular frequency band the trap presents a very high impedance (parallel resonance) effectively truncating the element at that length, making it a proper resonant antenna. At a lower frequency the trap allows the full length of the element to be employed, albeit with a shifted resonant frequency due to the inclusion of the trap's net reactance at that lower frequency.

qas: question: What is an acknowledgement of the range of possible direction for and antenna?
answers: text: gain

question: What is another way to refer to an antennas gain?
answers: text: power gain

question: What is the meaning of intensity?
answers: text: power per unit surface area

question: What type of an antenna would offer the same level of power to each possible destination?
answers: text: isotropic
context: Gain is a parameter which measures the degree of directivity of the antenna's radiation pattern. A high-gain antenna will radiate most of its power in a particular direction, while a low-gain antenna will radiate over a wider angle. The antenna gain, or power gain of an antenna is defined as the ratio of the intensity (power per unit surface area)  radiated by the antenna in the direction of its maximum output, at an arbitrary distance, divided by the intensity  radiated at the same distance by a hypothetical isotropic antenna which radiates equal power in all directions. This dimensionless ratio is usually expressed logarithmically in decibels, these units are called "decibels-isotropic" (dBi)

qas: question: Antennas with higher gain have what positive feature?
answers: text: longer range

question: Dish network Tv takes example of what type of antenna?
answers: text: parabolic dish

question: What type of antenna would be best if placement was tricky?
answers: text: Low-gain

question: What is a measure of how much efficient is improved by adding a device designed to make something stronger?
answers: text: amplifier gain
context: High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully at the other antenna. An example of a high-gain antenna is a parabolic dish such as a satellite television antenna. Low-gain antennas have shorter range, but the orientation of the antenna is relatively unimportant. An example of a low-gain antenna is the whip antenna found on portable radios and cordless phones. Antenna gain should not be confused with amplifier gain, a separate parameter measuring the increase in signal power due to an amplifying device.

qas: question: What must the relationship of an antenna and the receiving area be due to reciprocity?
answers: text: proportional

question: what could an antenna with complete electrical efficiency be said to have?
answers: text: no loss

question: hat could an antenna with complete electrical efficiency be said to have?
answers: text: 1

question: Another term for the effective area is?
answers: text: Aeff
context: Due to reciprocity (discussed above) the gain of an antenna used for transmitting must be proportional to its effective area when used for receiving. Consider an antenna with no loss, that is, one whose electrical efficiency is 100%. It can be shown that its effective area averaged over all directions must be equal to λ2/4π, the wavelength squared divided by 4π. Gain is defined such that the average gain over all directions for an antenna with 100% electrical efficiency is equal to 1. Therefore, the effective area Aeff in terms of the gain G in a given direction is given by:

qas: question: A plot of the radiation behaviors of an antenna would show what?
answers: text: relative field strength

question: What type of pictoral aid is often used to show this?
answers: text: three-dimensional graph

question:  A sphere shows what type of antennas radiation?
answers: text: isotropic

question: Dipoles are considered to be what antenna type?
answers: text: nondirectional

question: What would an omnidirectional antenna look like if plotted?
answers: text: donut
context: The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles. It is typically represented by a three-dimensional graph, or polar plots of the horizontal and vertical cross sections. The pattern of an ideal isotropic antenna, which radiates equally in all directions, would look like a sphere. Many nondirectional antennas, such as monopoles and dipoles, emit equal power in all horizontal directions, with the power dropping off at higher and lower angles; this is called an omnidirectional pattern and when plotted looks like a torus or donut.

qas: question: What is the term that refers to areas where an antennas radiation is zero? 
answers: text: nulls

question: What do radio waves do that account for maxima or nulls in an antenna pattern?
answers: text: interfere

question: If you desired to project radio waves to the south, what part of the antenna would you build larger in that direction?
answers: text: lobe

question: What is the main distinction of side lobes?
answers: text: represent unwanted radiation
context: The radiation of many antennas shows a pattern of maxima or "lobes" at various angles, separated by "nulls", angles where the radiation falls to zero. This is because the radio waves emitted by different parts of the antenna typically interfere, causing maxima at angles where the radio waves arrive at distant points in phase, and zero radiation at other angles where the radio waves arrive out of phase. In a directional antenna designed to project radio waves in a particular direction, the lobe in that direction is designed larger than the others and is called the "main lobe". The other lobes usually represent unwanted radiation and are called "sidelobes". The axis through the main lobe is called the "principal axis" or "boresight axis".

qas: question: What is one piece that makes up an antenna system?
answers: text: radio

question: What is created by a portion of a radio waves energy reversing?
answers: text: standing wave

question: A term that refers to the highs and lows of power in electro magnetic waves is?
answers: text: standing wave ratio

question: Impedance matching makes an important difference in what antenna function?
answers: text: power transfer
context: As an electro-magnetic wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc.). At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source, forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.

qas: question: A measure of the power that is useable and the power absorbed by the terminals?
answers: text: Efficiency

question: What happens to the power that is not absorbed by the antenna?
answers: text: heat

question: What can cause that reaction?
answers: text: transmitter
context: Efficiency of a transmitting antenna is the ratio of power actually radiated (in all directions) to the power absorbed by the antenna terminals. The power supplied to the antenna terminals which is not radiated is converted into heat. This is usually through loss resistance in the antenna's conductors, but can also be due to dielectric or magnetic core losses in antennas (or antenna systems) using such components. Such loss effectively robs power from the transmitter, requiring a stronger transmitter in order to transmit a signal of a given strength.

qas: question: What would need to be placed into the transmitter to create ten W oh warmth? 
answers: text: 100 W

question: What factor may play a hand in lessened power from a transmitter?
answers: text: impedance matching

question: What would need to be investigated to determine how much power was radiated?
answers: text: electrical measurements
context: For instance, if a transmitter delivers 100 W into an antenna having an efficiency of 80%, then the antenna will radiate 80 W as radio waves and produce 20 W of heat. In order to radiate 100 W of power, one would need to use a transmitter capable of supplying 125 W to the antenna. Note that antenna efficiency is a separate issue from impedance matching, which may also reduce the amount of power radiated using a given transmitter. If an SWR meter reads 150 W of incident power and 50 W of reflected power, that means that 100 W have actually been absorbed by the antenna (ignoring transmission line losses). How much of that power has actually been radiated cannot be directly determined through electrical measurements at (or before) the antenna terminals, but would require (for instance) careful measurement of field strength. Fortunately the loss resistance of antenna conductors such as aluminum rods can be calculated and the efficiency of an antenna using such materials predicted.

qas: question: What can increase the feedpoint impedance of a component?
answers: text: loss resistance

question: The addition of Rr and Rloss equals what?
answers: text: resistance

question: What equation an determine an antennas effectiveness?
answers: text: Rr / (Rr + Rloss)

question: What is the single factor that can be precisely measured?
answers: text: total resistance
context: However loss resistance will generally affect the feedpoint impedance, adding to its resistive (real) component. That resistance will consist of the sum of the radiation resistance Rr and the loss resistance Rloss. If an rms current I is delivered to the terminals of an antenna, then a power of I2Rr will be radiated and a power of I2Rloss will be lost as heat. Therefore, the efficiency of an antenna is equal to Rr / (Rr + Rloss). Of course only the total resistance Rr + Rloss can be directly measured.

qas: question: In what type of programs would low efficiency antennas not make a difference in effectiveness?
answers: text: receiving

question: At lesser frequencies what can account for incorrect assumptions about efficiency?
answers: text: man-made noise

question: What is the median level for measuring atmospheric noise?
answers: text: thermal noise floor

question: What is SNR?
answers: text: signal to noise ratio
context: According to reciprocity, the efficiency of an antenna used as a receiving antenna is identical to the efficiency as defined above. The power that an antenna will deliver to a receiver (with a proper impedance match) is reduced by the same amount. In some receiving applications, the very inefficient antennas may have little impact on performance. At low frequencies, for example, atmospheric or man-made noise can mask antenna inefficiency. For example, CCIR Rep. 258-3 indicates man-made noise in a residential setting at 40 MHz is about 28 dB above the thermal noise floor. Consequently, an antenna with a 20 dB loss (due to inefficiency) would have little impact on system noise performance. The loss within the antenna will affect the intended signal and the noise/interference identically, leading to no reduction in signal to noise ratio (SNR).

qas: question: What else is also known as power gain?
answers: text: antenna gain

question: What is used to signal toward a reciever?
answers: text: transmitter

question: Which gain does not iclude the effect of an antenna?
answers: text: directive gain

question: Wats divided by the antennas efficiency?
answers: text: published gain
context: The definition of antenna gain or power gain already includes the effect of the antenna's efficiency. Therefore, if one is trying to radiate a signal toward a receiver using a transmitter of a given power, one need only compare the gain of various antennas rather than considering the efficiency as well. This is likewise true for a receiving antenna at very high (especially microwave) frequencies, where the point is to receive a signal which is strong compared to the receiver's noise temperature. However, in the case of a directional antenna used for receiving signals with the intention of rejecting interference from different directions, one is no longer concerned with the antenna efficiency, as discussed above. In this case, rather than quoting the antenna gain, one would be more concerned with the directive gain which does not include the effect of antenna (in)efficiency. The directive gain of an antenna can be computed from the published gain divided by the antenna's efficiency.

qas: question: Small and minimal frequency antennas are know to be what?
answers: text: inefficient

question: What is added to to increase ability for reception?
answers: text: small loop antenna

question: How would this antenna rate in the greater scheme of things?
answers: text: little effect

question: When talking about much larger network what effect can reduced antenna effectiveness have?
answers: text: substantial cost
context: This is fortunate, since antennas at lower frequencies which are not rather large (a good fraction of a wavelength in size) are inevitably inefficient (due to the small radiation resistance Rr of small antennas). Most AM broadcast radios (except for car radios) take advantage of this principle by including a small loop antenna for reception which has an extremely poor efficiency. Using such an inefficient antenna at this low frequency (530–1650 kHz) thus has little effect on the receiver's net performance, but simply requires greater amplification by the receiver's electronics. Contrast this tiny component to the massive and very tall towers used at AM broadcast stations for transmitting at the very same frequency, where every percentage point of reduced antenna efficiency entails a substantial cost.

qas: question: What is another name for electric-field?
answers: text: E-plane

question: How many polarizations will a antenna have when mounted vertically?
answers: text: one

question: Whats understood in reference of direction of an E-plane?
answers: text: polarization

question: When is a magnetic fields right angles to a electrical field?
answers: text: transverse wave
context: The polarization of an antenna refers to the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation; note that this designation is totally distinct from the antenna's directionality. Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally. As a transverse wave, the magnetic field of a radio wave is at right angles to that of the electric field, but by convention, talk of an antenna's "polarization" is understood to refer to the direction of the electric field.

qas: question: What mostly affects polarization?
answers: text: Reflections

question: What reflector can change the waves polarization?
answers: text: ionosphere

question: What will you be matching with the  receiving antenna's polarization?
answers: text: transmitter

question: What stays the same regarding polarization state at the recieving location?
answers: text: polarized transmissions

question: What is the name used for signals recieved following reflection by the ionosphere?
answers: text: a skywave
context: Reflections generally affect polarization. For radio waves, one important reflector is the ionosphere which can change the wave's polarization. Thus for signals received following reflection by the ionosphere (a skywave), a consistent polarization cannot be expected. For line-of-sight communications or ground wave propagation, horizontally or vertically polarized transmissions generally remain in about the same polarization state at the receiving location. Matching the receiving antenna's polarization to that of the transmitter can make a very substantial difference in received signal strength.

qas: question: Whats predictable about an antenna's geometry?
answers: text: Polarization

question: What is a more complicated type of polarization from an antenna's geometry?
answers: text: quad antenna

question: The polarization of what antenna is essential specification?
answers: text: commercial antenna

question: Most rooftop antenna's are polarized in which direction?
answers: text: horizontal
context: Polarization is predictable from an antenna's geometry, although in some cases it is not at all obvious (such as for the quad antenna). An antenna's linear polarization is generally along the direction (as viewed from the receiving location) of the antenna's currents when such a direction can be defined. For instance, a vertical whip antenna or Wi-Fi antenna vertically oriented will transmit and receive in the vertical polarization. Antennas with horizontal elements, such as most rooftop TV antennas in the United States, are horizontally polarized (broadcast TV in the U.S. usually uses horizontal polarization). Even when the antenna system has a vertical orientation, such as an array of horizontal dipole antennas, the polarization is in the horizontal direction corresponding to the current flow. The polarization of a commercial antenna is an essential specification.

qas: question: What are electrical fields projected on to?
answers: text: imaginary plane

question: What is the imagenary plane perpindicular to?
answers: text: radio wave

question: What is the name to describe polarization of radio waves varies over times?
answers: text: elliptical

question: How many directions does the E-plane of the radio waves oscillates back and forth?
answers: text: one direction
context: Polarization is the sum of the E-plane orientations over time projected onto an imaginary plane perpendicular to the direction of motion of the radio wave. In the most general case, polarization is elliptical, meaning that the polarization of the radio waves varies over time. Two special cases are linear polarization (the ellipse collapses into a line) as we have discussed above, and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the electric field of the radio wave oscillates back and forth along one direction; this can be affected by the mounting of the antenna but usually the desired direction is either horizontal or vertical polarization. In circular polarization, the electric field (and magnetic field) of the radio wave rotates at the radio frequency circularly around the axis of propagation. Circular or elliptically polarized radio waves are designated as right-handed or left-handed using the "thumb in the direction of the propagation" rule. Note that for circular polarization, optical researchers use the opposite right hand rule from the one used by radio engineers.

qas: question: What is the best for an recieving antenna for optimum reception?
answers: text: match the polarization

question: What loses signal strength?
answers: text: Intermediate matchings

question: What is used to match vertical and horizontal linear polarizations?
answers: text: circularly polarized

question: A transmission can cause reduction in what?
answers: text: signal-to-noise ratio
context: It is best for the receiving antenna to match the polarization of the transmitted wave for optimum reception. Intermediate matchings will lose some signal strength, but not as much as a complete mismatch. A circularly polarized antenna can be used to equally well match vertical or horizontal linear polarizations. Transmission from a circularly polarized antenna received by a linearly polarized antenna (or vice versa) entails a 3 dB reduction in signal-to-noise ratio as the received power has thereby been cut in half.

qas: question: What requires matching of the empedance to an antenna system?
answers: text: Maximum power transfer

question: What is the desired design value for transmmiting circuitry?
answers: text: 50 ohms

question: Why would a transmitter have additional adjustments?
answers: text: "tweak" the match

question: What is SWR?
answers: text: standing wave ratio
context: Maximum power transfer requires matching the impedance of an antenna system (as seen looking into the transmission line) to the complex conjugate of the impedance of the receiver or transmitter. In the case of a transmitter, however, the desired matching impedance might not correspond to the dynamic output impedance of the transmitter as analyzed as a source impedance but rather the design value (typically 50 ohms) required for efficient and safe operation of the transmitting circuitry. The intended impedance is normally resistive but a transmitter (and some receivers) may have additional adjustments to cancel a certain amount of reactance in order to "tweak" the match. When a transmission line is used in between the antenna and the transmitter (or receiver) one generally would like an antenna system whose impedance is resistive and near the characteristic impedance of that transmission line in order to minimize the standing wave ratio (SWR) and the increase in transmission line losses it entails, in addition to supplying a good match at the transmitter or receiver itself.

qas: question: What can be shorter than 1/4 wavelength long?
answers: text: whip antenna

question: What is the opposite of inductive reactance?
answers: text: capacitative reactance

question: What is at the base of the antenna?
answers: text: loading coil

question: Where is the resistance seen on the loading foil?
answers: text: feedpoint
context: In some cases this is done in a more extreme manner, not simply to cancel a small amount of residual reactance, but to resonate an antenna whose resonance frequency is quite different from the intended frequency of operation. For instance, a "whip antenna" can be made significantly shorter than 1/4 wavelength long, for practical reasons, and then resonated using a so-called loading coil. This physically large inductor at the base of the antenna has an inductive reactance which is the opposite of the capacitative reactance that such a vertical antenna has at the desired operating frequency. The result is a pure resistance seen at feedpoint of the loading coil; unfortunately that resistance is somewhat lower than would be desired to match commercial coax.[citation needed]

qas: question: What is not adjustable when it comes to a transformer?
answers: text: turns ratio

question: A general matching network needs a minimum of how many adjustments to correct all components of impedance?
answers: text: two adjustments

question: How many ohms are in are in a standard coax?
answers: text: 50 or 75

question: What is included between the transmission line and the antenna element?
answers: text: balun

question: A balun should be integrated into what?
answers: text: matching network
context: So an additional problem beyond canceling the unwanted reactance is of matching the remaining resistive impedance to the characteristic impedance of the transmission line. In principle this can always be done with a transformer, however the turns ratio of a transformer is not adjustable. A general matching network with at least two adjustments can be made to correct both components of impedance. Matching networks using discrete inductors and capacitors will have losses associated with those components, and will have power restrictions when used for transmitting. Avoiding these difficulties, commercial antennas are generally designed with fixed matching elements or feeding strategies to get an approximate match to standard coax, such as 50 or 75 Ohms. Antennas based on the dipole (rather than vertical antennas) should include a balun in between the transmission line and antenna element, which may be integrated into any such matching network.

qas: question: What antenna's are nonresonant?
answers: text: traveling wave antennas

question: How long are the wire antenna's that the voltage and current waves travel in the same direction?
answers: text: one direction

question: What antenna does not have linear polarization?
answers: text: helical antenna

question: What are undirectional traveling wave directions terminated by?
answers: text: resistor

question: What is the resistor equal to?
answers: text: antenna's characteristic resistance
context: Unlike the above antennas, traveling wave antennas are nonresonant so they have inherently broad bandwidth. They are typically wire antennas multiple wavelengths long, through which the voltage and current waves travel in one direction, instead of bouncing back and forth to form standing waves as in resonant antennas. They have linear polarization (except for the helical antenna). Unidirectional traveling wave antennas are terminated by a resistor at one end equal to the antenna's characteristic resistance, to absorb the waves from one direction. This makes them inefficient as transmitting antennas.

qas: question: What is the radiation patter influenced by?
answers: text: dielectric constant

question: The ground is important for what antenna?
answers: text: terrestrial antenna

question: Whats another name for the ground?
answers: text: artificial ground plane

question: What does the artificial ground plane do for the antenna current?
answers: text: return connection
context: The radiation pattern and even the driving point impedance of an antenna can be influenced by the dielectric constant and especially conductivity of nearby objects. For a terrestrial antenna, the ground is usually one such object of importance. The antenna's height above the ground, as well as the electrical properties (permittivity and conductivity) of the ground, can then be important. Also, in the particular case of a monopole antenna, the ground (or an artificial ground plane) serves as the return connection for the antenna current thus having an additional effect, particularly on the impedance seen by the feed line.

qas: question: What is the net quality of the ground dependent of?
answers: text: topography

question: What is the reason for the receiver seeing both the ral antenna and image of the antenna?
answers: text: reflection

question: What frequencies is associated with shorter wavelengths?
answers: text: higher frequencies

question: When will reflections not be coherent?
answers: text: ground has irregularities
context: The net quality of a ground reflection depends on the topography of the surface. When the irregularities of the surface are much smaller than the wavelength, we are in the regime of specular reflection, and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. But if the ground has irregularities not small compared to the wavelength, reflections will not be coherent but shifted by random phases. With shorter wavelengths (higher frequencies), this is generally the case.

qas: question: What is the refractive index of the ground?
answers: text: n=2

question: What is the refractive index of air?
answers: text: n=1

question: When is polarized radiation reversed?
answers: text: reflection

question: Besides a ground, what has these phases apply well to?
answers: text: electrical conductor
context: The phase of reflection of electromagnetic waves depends on the polarization of the incident wave. Given the larger refractive index of the ground (typically n=2) compared to air (n=1), the phase of horizontally polarized radiation is reversed upon reflection (a phase shift of  radians or 180°). On the other hand, the vertical component of the wave's electric field is reflected at grazing angles of incidence approximately in phase. These phase shifts apply as well to a ground modelled as a good electrical conductor.

qas: question: what is reflected and transmitted into the ground when a plane surface is struck?
answers: text: electromagnetic wave

question: Who proposed this theory?
answers: text: Fresnel coefficients

question: Is the ground has a great conductor, how much of the wave will be reflected?
answers: text: 180° out of phase

question: What depends on the polarization and waves angle?
answers: text: power remaining
context: When an electromagnetic wave strikes a plane surface such as the ground, part of the wave is transmitted into the ground and part of it is reflected, according to the Fresnel coefficients. If the ground is a very good conductor then almost all of the wave is reflected (180° out of phase), whereas a ground modeled as a (lossy) dielectric can absorb a large amount of the wave's power. The power remaining in the reflected wave, and the phase shift upon reflection, strongly depend on the wave's angle of incidence and polarization. The dielectric constant and conductivity (or simply the complex dielectric constant) is dependent on the soil type and is a function of frequency.

qas: question: What is the portion of something that is reached by the radio transmission called?
answers: text: aperture

question: What is a measure of the power of an antenna?
answers: text: microvolts

question: What effects the function of signals received by an antenna?
answers: text: direction

question: How much power will be delivered to the reciever if the antenna has an effective area of 12 m/2?
answers: text: 12 pW of RF power
context: The effective area or effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave which it delivers to its terminals, expressed in terms of an equivalent area. For instance, if a radio wave passing a given location has a flux of 1 pW / m2 (10−12 watts per square meter) and an antenna has an effective area of 12 m2, then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts rms at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source.

qas: question: The properties of a usable radio frequency can be called its?
answers: text: Q

question: What is a measure of the comparison between reactance and resistance?
answers: text: Q

question: What is the largest Q that could be achieved with a slimmer band antenna?
answers: text: 15

question: What type of element would be used to encounter less reactance?
answers: text: thick
context: The bandwidth characteristics of a resonant antenna element can be characterized according to its Q, just as one uses to characterize the sharpness of an L-C resonant circuit. However it is often assumed that there is an advantage in an antenna having a high Q. After all, Q is short for "quality factor" and a low Q typically signifies excessive loss (due to unwanted resistance) in a resonant L-C circuit. However this understanding does not apply to resonant antennas where the resistance involved is the radiation resistance, a desired quantity which removes energy from the resonant element in order to radiate it (the purpose of an antenna, after all!). The Q is a measure of the ratio of reactance to resistance, so with a fixed radiation resistance (an element's radiation resistance is almost independent of its diameter) a greater reactance off-resonance corresponds to the poorer bandwidth of a very thin conductor. The Q of such a narrowband antenna can be as high as 15. On the other hand, a thick element presents less reactance at an off-resonant frequency, and consequently a Q as low as 5. These two antennas will perform equivalently at the resonant frequency, but the second antenna will perform over a bandwidth 3 times as wide as the "hi-Q" antenna consisting of a thin conductor.

qas: question: What can be added to allow for an antenna shorter than the needed height to produce desired results?
answers: text: loading coil

question: How would the resistive impedance from this scenario compare to if the antenna was the proper height?
answers: text: lower

question: The coil has lengthed the antenna to reach how much length electrically?
answers: text: 2.5 meters

question: What is the major thing that sets the size of antennas at lower frequencies?
answers: text: reactance
context: For example, at 30 MHz (10 m wavelength) a true resonant 1⁄4-wavelength monopole would be almost 2.5 meters long, and using an antenna only 1.5 meters tall would require the addition of a loading coil. Then it may be said that the coil has lengthened the antenna to achieve an electrical length of 2.5 meters. However, the resulting resistive impedance achieved will be quite a bit lower than the impedance of a resonant monopole, likely requiring further impedance matching. In addition to a lower radiation resistance, the reactance becomes higher as the antenna size is reduced, and the resonant circuit formed by the antenna and the tuning coil has a Q factor that rises and eventually causes the bandwidth of the antenna to be inadequate for the signal being transmitted. This is the major factor that sets the size of antennas at 1 MHz and lower frequencies.

qas: question: How big would an antenna be used to with with one m wavelengths?
answers: text: 50 cm

question: How could the rection of output be adressed by?
answers: text: changing the matching system

question:  What unit is used to measure current?
answers: text: ampere

question: What effect occurs when the signal is reflected back into the antenna?
answers: text: reducing output
context: Consider a half-wave dipole designed to work with signals 1 m wavelength, meaning the antenna would be approximately 50 cm across. If the element has a length-to-diameter ratio of 1000, it will have an inherent resistance of about 63 ohms. Using the appropriate transmission wire or balun, we match that resistance to ensure minimum signal loss. Feeding that antenna with a current of 1 ampere will require 63 volts of RF, and the antenna will radiate 63 watts (ignoring losses) of radio frequency power. Now consider the case when the antenna is fed a signal with a wavelength of 1.25 m; in this case the reflected current would arrive at the feed out-of-phase with the signal, causing the net current to drop while the voltage remains the same. Electrically this appears to be a very high impedance. The antenna and transmission line no longer have the same impedance, and the signal will be reflected back into the antenna, reducing output. This could be addressed by changing the matching system between the antenna and transmission line, but that solution only works well at the new design frequency.

qas: question: What sort of changes in material would a current reflect?
answers: text: electrical

question:  What must match between the transmission line and elements?
answers: text: impedance

question: What technique is used to prevent unintentional decrease in signal?
answers: text: Impedance matching

question: How is this process usually used for transmission lines and antennas?
answers: text: balun
context: Recall that a current will reflect when there are changes in the electrical properties of the material. In order to efficiently send the signal into the transmission line, it is important that the transmission line has the same impedance as the elements, otherwise some of the signal will be reflected back into the antenna. This leads to the concept of impedance matching, the design of the overall system of antenna and transmission line so the impedance is as close as possible, thereby reducing these losses. Impedance matching between antennas and transmission lines is commonly handled through the use of a balun, although other solutions are also used in certain roles. An important measure of this basic concept is the standing wave ratio, which measures the magnitude of the reflected signal.

qas: question: What is used to allow one to control the function of wave fronts moving through an antenna?
answers: text: selectively delay

question: What changes the structuak traits of a wave on either side?
answers: text: refractor

question: What is the main purpose of a refractor?
answers: text: spatial characteristics

question: A refractor can be compared to what type of viewing?
answers: text: optical lens
context: An electromagnetic wave refractor in some aperture antennas is a component which due to its shape and position functions to selectively delay or advance portions of the electromagnetic wavefront passing through it. The refractor alters the spatial characteristics of the wave on one side relative to the other side. It can, for instance, bring the wave to a focus or alter the wave front in other ways, generally in order to maximize the directivity of the antenna system. This is the radio equivalent of an optical lens.

qas: question: What can receive a stron signal by transmitting an original wave?
answers: text: actual antenna

question: Where will the additional current be induced?
answers: text: antenna element

question: What is altered because of the proximity to the ground?
answers: text: antenna's impedance

question: what happens to the reflected wave which allows the antenna to reach its asympotic feedpoint impedance?
answers: text: reduced power
context: The actual antenna which is transmitting the original wave then also may receive a strong signal from its own image from the ground. This will induce an additional current in the antenna element, changing the current at the feedpoint for a given feedpoint voltage. Thus the antenna's impedance, given by the ratio of feedpoint voltage to current, is altered due to the antenna's proximity to the ground. This can be quite a significant effect when the antenna is within a wavelength or two of the ground. But as the antenna height is increased, the reduced power of the reflected wave (due to the inverse square law) allows the antenna to approach its asymptotic feedpoint impedance given by theory. At lower heights, the effect on the antenna's impedance is very sensitive to the exact distance from the ground, as this affects the phase of the reflected wave relative to the currents in the antenna. Changing the antenna's height by a quarter wavelength, then changes the phase of the reflection by 180°, with a completely different effect on the antenna's impedance.

qas: question: What is between recieving and transmitting antenna's?
answers: text: horizontal propagation

question: When is the emission at maximized recieved signal?
answers: text: polarized vertically

question: Where is the radiation patterns in the vertical plane shown?
answers: text: image at right

question: What is also increased along with the antenna's height?
answers: text: lobes
context: For horizontal propagation between transmitting and receiving antennas situated near the ground reasonably far from each other, the distances traveled by tne direct and reflected rays are nearly the same. There is almost no relative phase shift. If the emission is polarized vertically, the two fields (direct and reflected) add and there is maximum of received signal. If the signal is polarized horizontally, the two signals subtract and the received signal is largely cancelled. The vertical plane radiation patterns are shown in the image at right. With vertical polarization there is always a maximum for θ=0, horizontal propagation (left pattern). For horizontal polarization, there is cancellation at that angle. Note that the above formulae and these plots assume the ground as a perfect conductor. These plots of the radiation pattern correspond to a distance between the antenna and its image of 2.5λ. As the antenna height is increased, the number of lobes increases as well.

qas: question: What is another name for classical television transmissions?
answers: text: analog

question: Buildings can create ghost images because of what?
answers: text: multipath propagation

question: When is ghosting reduced?
answers: text: horizontal polarization

question: What cause less problems in digital terrestrial television?
answers: text: Vertically polarized analog television
context: On the other hand, classical (analog) television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection of electromagnetic waves in the p polarization (horizontal polarization off the side of a building) is generally less than s (vertical, in this case) polarization. Vertically polarized analog television has nevertheless been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction.

qas: question: Where are the indiviual array elements known?
answers: text: antenna arrays

question: What induces a feedpoint to antennas nearby?
answers: text: Current circulating

question: What are the mathmatic useful towards?
answers: text: electrical behaviour

question: What cause mutual interactions between the elements electric and magnetic fields?
answers: text: proximity
context: Current circulating in one antenna generally induces a voltage across the feedpoint of nearby antennas or antenna elements. The mathematics presented below are useful in analyzing the electrical behaviour of antenna arrays, where the properties of the individual array elements (such as half wave dipoles) are already known. If those elements were widely separated and driven in a certain amplitude and phase, then each would act independently as that element is known to. However, because of the mutual interaction between their electric and magnetic fields due to proximity, the currents in each element are not simply a function of the applied voltage (according to its driving point impedance), but depend on the currents in the other nearby elements. Note that this now is a near field phenomenon which could not be properly accounted for using the Friis transmission equation for instance.

qas: question: a antenna element not connected to anything is circuited how?
answers: text: open circuited

question: When is the element not allowed voltage?
answers: text: short circuited

question: What element absorbs and reradiate RF-energy?
answers: text: Parasitic

question: What antenna can the solid rod be viewed as a dipole antenna?
answers: text: Yagi-Uda

question: Where can this solid rod be viewed?
answers: text: feedpoint
context: This is a consequence of Lorentz reciprocity. For an antenna element  not connected to anything (open circuited) one can write . But for an element  which is short circuited, a current is generated across that short but no voltage is allowed, so the corresponding . This is the case, for instance, with the so-called parasitic elements of a Yagi-Uda antenna where the solid rod can be viewed as a dipole antenna shorted across its feedpoint. Parasitic elements are unpowered elements that absorb and reradiate RF energy according to the induced current calculated using such a system of equations.

qas: question: What type of programmin relies on vertical polarization?
answers: text: broadcasting

question: If you were to position your receiver closer to the ground what might be a negative of this placement?
answers: text: cancellation

question: What is one use that would require an antenna to receive signals in various ways at once?
answers: text: mobile phones

question: If you were to develop a signal to be used with mobile phones what would be an effective antenna type?
answers: text: circular polarization.

question: What would the antenna you are using take advantage of to allow it to work in multiple locations?
answers: text: mixed polarization
context: The difference in the above factors for the case of θ=0 is the reason that most broadcasting (transmissions intended for the public) uses vertical polarization. For receivers near the ground, horizontally polarized transmissions suffer cancellation. For best reception the receiving antennas for these signals are likewise vertically polarized. In some applications where the receiving antenna must work in any position, as in mobile phones, the base station antennas use mixed polarization, such as linear polarization at an angle (with both vertical and horizontal components) or circular polarization.

qas: question: What type of antenna can be formed by a circular segment of wire?
answers: text: Loop antennas

question: What is a loop antenna compared with to determine its beahvior?
answers: text: circumference of a wavelength

question: If you needed to place an antenna somewhere with a large amount of interference, which type would be best?
answers: text: loops small

question: Why would this type be good for receiving but not transmtting?
answers: text: low radiation resistance

question: What else would be an effective application of this antenna type?
answers: text: direction finding
context: Loop antennas consist of a loop or coil of wire. Loops with circumference of a wavelength or larger act similarly to dipole antennas. However loops small in comparison to a wavelength act differently. They interact with the magnetic field of the radio wave instead of the electric field as other antennas do, and so are relatively insensitive to nearby electrical noise. However they have low radiation resistance, and so are inefficient for transmitting. They are used as receiving antennas at low frequencies, and also as direction finding antennas.

qas: question: Are essential properties of an antenna changed based on what fungtion they are performing
answers: text: the same

question: What proposition explains the equivalency of the recieving pattern of an antenna?
answers: text: reciprocity theorem of electromagnetics

question: Can the antenna serve more than one fungtion at a time?
answers: text: either transmitting or receiving

question: What is one electrical trait of an antenna?
answers: text: radiation pattern
context: It is a fundamental property of antennas that the electrical characteristics of an antenna described in the next section, such as gain, radiation pattern, impedance, bandwidth, resonant frequency and polarization, are the same whether the antenna is transmitting or receiving. For example, the "receiving pattern" (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator. This is a consequence of the reciprocity theorem of electromagnetics. Therefore, in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient.