rajpurkar/squad huggingface dataset:
Title: Antenna_(radio)

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.

Question: The properties of a usable radio frequency can be called its?
Answer: Q

Question: What is a measure of the comparison between reactance and resistance?
Answer: Q

Question: What is the largest Q that could be achieved with a slimmer band antenna?
Answer: 15

Question: What type of element would be used to encounter less reactance?
Answer: thick
Title: Antenna_(radio)

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.

Question: What can be added to allow for an antenna shorter than the needed height to produce desired results?
Answer: loading coil

Question: How would the resistive impedance from this scenario compare to if the antenna was the proper height?
Answer: lower

Question: The coil has lengthed the antenna to reach how much length electrically?
Answer: 2.5 meters

Question: What is the major thing that sets the size of antennas at lower frequencies?
Answer: reactance
Title: Antenna_(radio)

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.

Question: How big would an antenna be used to with with one m wavelengths?
Answer: 50 cm

Question: How could the rection of output be adressed by?
Answer: changing the matching system

Question:  What unit is used to measure current?
Answer: ampere

Question: What effect occurs when the signal is reflected back into the antenna?
Answer: reducing output
Title: Antenna_(radio)

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.

Question: What sort of changes in material would a current reflect?
Answer: electrical

Question:  What must match between the transmission line and elements?
Answer: impedance

Question: What technique is used to prevent unintentional decrease in signal?
Answer: Impedance matching

Question: How is this process usually used for transmission lines and antennas?
Answer: balun
Title: Antenna_(radio)

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.

Question: What is used to allow one to control the function of wave fronts moving through an antenna?
Answer: selectively delay

Question: What changes the structuak traits of a wave on either side?
Answer: refractor

Question: What is the main purpose of a refractor?
Answer: spatial characteristics

Question: A refractor can be compared to what type of viewing?
Answer: optical lens
Title: Antenna_(radio)

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.

Question: What can receive a stron signal by transmitting an original wave?
Answer: actual antenna

Question: Where will the additional current be induced?
Answer: antenna element

Question: What is altered because of the proximity to the ground?
Answer: antenna's impedance

Question: what happens to the reflected wave which allows the antenna to reach its asympotic feedpoint impedance?
Answer: reduced power
Title: Antenna_(radio)

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.

Question: What is between recieving and transmitting antenna's?
Answer: horizontal propagation

Question: When is the emission at maximized recieved signal?
Answer: polarized vertically

Question: Where is the radiation patterns in the vertical plane shown?
Answer: image at right

Question: What is also increased along with the antenna's height?
Answer: lobes
Title: Antenna_(radio)

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.

Question: What is another name for classical television transmissions?
Answer: analog

Question: Buildings can create ghost images because of what?
Answer: multipath propagation

Question: When is ghosting reduced?
Answer: horizontal polarization

Question: What cause less problems in digital terrestrial television?
Answer: Vertically polarized analog television
Title: Antenna_(radio)

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.

Question: Where are the indiviual array elements known?
Answer: antenna arrays

Question: What induces a feedpoint to antennas nearby?
Answer: Current circulating

Question: What are the mathmatic useful towards?
Answer: electrical behaviour

Question: What cause mutual interactions between the elements electric and magnetic fields?
Answer: proximity
Title: Antenna_(radio)

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.

Question: a antenna element not connected to anything is circuited how?
Answer: open circuited

Question: When is the element not allowed voltage?
Answer: short circuited

Question: What element absorbs and reradiate RF-energy?
Answer: Parasitic

Question: What antenna can the solid rod be viewed as a dipole antenna?
Answer: Yagi-Uda

Question: Where can this solid rod be viewed?
Answer: feedpoint
Title: Antenna_(radio)

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.

Question: What type of programmin relies on vertical polarization?
Answer: broadcasting

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

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

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

Question: What would the antenna you are using take advantage of to allow it to work in multiple locations?
Answer: mixed polarization
Title: Antenna_(radio)

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.

Question: What type of antenna can be formed by a circular segment of wire?
Answer: Loop antennas

Question: What is a loop antenna compared with to determine its beahvior?
Answer: circumference of a wavelength

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

Question: Why would this type be good for receiving but not transmtting?
Answer: low radiation resistance

Question: What else would be an effective application of this antenna type?
Answer: direction finding
Title: Antenna_(radio)

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.

Question: Are essential properties of an antenna changed based on what fungtion they are performing
Answer: the same

Question: What proposition explains the equivalency of the recieving pattern of an antenna?
Answer: reciprocity theorem of electromagnetics

Question: Can the antenna serve more than one fungtion at a time?
Answer: either transmitting or receiving

Question: What is one electrical trait of an antenna?
Answer: radiation pattern
Title: Flowering_plant

The flowering plants (angiosperms), also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants, with about 350,000 species. Like gymnosperms, angiosperms are seed-producing plants; they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, and the production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces seeds within an enclosure, in other words, a fruiting plant. The term "angiosperm" comes from the Greek composite word (angeion-, "case" or "casing", and sperma, "seed") meaning "enclosed seeds", after the enclosed condition of the seeds.

Question: What are the most diverse group of land plants?
Answer: angiosperms

Question: How many species of flowering plants are there about?
Answer: 350,000

Question: What does an angiosperm produce its seeds within?
Answer: an enclosure

Question: What do angiosperms have in common with gymnosperms?
Answer: seed-producing plants

Question: What is the Greek word for "case" or "casing"?
Answer: angeion
Title: Flowering_plant

Fossilized spores suggest that higher plants (embryophytes) have lived on land for at least 475 million years. Early land plants reproduced sexually with flagellated, swimming sperm, like the green algae from which they evolved. An adaptation to terrestrialization was the development of upright meiosporangia for dispersal by spores to new habitats. This feature is lacking in the descendants of their nearest algal relatives, the Charophycean green algae. A later terrestrial adaptation took place with retention of the delicate, avascular sexual stage, the gametophyte, within the tissues of the vascular sporophyte. This occurred by spore germination within sporangia rather than spore release, as in non-seed plants. A current example of how this might have happened can be seen in the precocious spore germination in Selaginella, the spike-moss. The result for the ancestors of angiosperms was enclosing them in a case, the seed. The first seed bearing plants, like the ginkgo, and conifers (such as pines and firs), did not produce flowers. The pollen grains (males) of Ginkgo and cycads produce a pair of flagellated, mobile sperm cells that "swim" down the developing pollen tube to the female and her eggs.

Question: How long have higher plants lived on land?
Answer: at least 475 million years

Question: How did early plants reproduce sexually?
Answer: with flagellated, swimming sperm

Question: Upright meisporangia allowed what to be dispersed to new habitats?
Answer: spores

Question: What are the nearest algal relatives existing today?
Answer: Charophycean green algae

Question: What is the common name for Selaginella?
Answer: the spike-moss
Title: Flowering_plant

The apparently sudden appearance of nearly modern flowers in the fossil record initially posed such a problem for the theory of evolution that it was called an "abominable mystery" by Charles Darwin. However, the fossil record has considerably grown since the time of Darwin, and recently discovered angiosperm fossils such as Archaefructus, along with further discoveries of fossil gymnosperms, suggest how angiosperm characteristics may have been acquired in a series of steps. Several groups of extinct gymnosperms, in particular seed ferns, have been proposed as the ancestors of flowering plants, but there is no continuous fossil evidence showing exactly how flowers evolved. Some older fossils, such as the upper Triassic Sanmiguelia, have been suggested. Based on current evidence, some propose that the ancestors of the angiosperms diverged from an unknown group of gymnosperms in the Triassic period (245–202 million years ago). Fossil angiosperm-like pollen from the Middle Triassic (247.2–242.0 Ma) suggests an older date for their origin. A close relationship between angiosperms and gnetophytes, proposed on the basis of morphological evidence, has more recently been disputed on the basis of molecular evidence that suggest gnetophytes are instead more closely related to other gymnosperms.[citation needed]

Question: What did Charles Darwin call the sudden appearance of nearly modern flowers in the fossil record?
Answer: abominable mystery

Question: What type of fossil is the recently discovered Archaefructus?
Answer: angiosperm

Question: What fossil evidence is lacking when it comes to flowers?
Answer: evidence showing exactly how flowers evolved

Question: From what period does fossilized pollen suggest an older date for angiosperm origin?
Answer: Middle Triassic

Question: What relationship proposed on the basis of morphological evidence has recently been disputed?
Answer: relationship between angiosperms and gnetophytes
Title: Flowering_plant

The evolution of seed plants and later angiosperms appears to be the result of two distinct rounds of whole genome duplication events. These occurred at 319 million years ago and 192 million years ago. Another possible whole genome duplication event at 160 million years ago perhaps created the ancestral line that led to all modern flowering plants. That event was studied by sequencing the genome of an ancient flowering plant, Amborella trichopoda, and directly addresses Darwin's "abominable mystery."

Question: How many distinct rounds of genome duplication events are suspected in the evolution of seed plants?
Answer: two

Question: When did the first whole genome duplication event occur?
Answer: 319 million years ago

Question: What type of event perhaps created the line which led to modern flowering plants?
Answer: whole genome duplication

Question: How are duplication events studied?
Answer: by sequencing the genome of an ancient flowering plant

Question: Who coined the term "abominable mystery"?
Answer: Darwin
Title: Flowering_plant

The earliest known macrofossil confidently identified as an angiosperm, Archaefructus liaoningensis, is dated to about 125 million years BP (the Cretaceous period), whereas pollen considered to be of angiosperm origin takes the fossil record back to about 130 million years BP. However, one study has suggested that the early-middle Jurassic plant Schmeissneria, traditionally considered a type of ginkgo, may be the earliest known angiosperm, or at least a close relative. In addition, circumstantial chemical evidence has been found for the existence of angiosperms as early as 250 million years ago. Oleanane, a secondary metabolite produced by many flowering plants, has been found in Permian deposits of that age together with fossils of gigantopterids. Gigantopterids are a group of extinct seed plants that share many morphological traits with flowering plants, although they are not known to have been flowering plants themselves.

Question: When is the earliest known macrofossil identified as an angiosperm dated?
Answer: about 125 million years BP

Question: What is the earliest known angiosperm?
Answer: Archaefructus liaoningensis

Question: What pushes the age of angiosperm 5 million years further back?
Answer: pollen

Question: How long ago has circumstantial evidence has been found for the existence of angiosperms?
Answer: 250 million years ago

Question: What group of now extinct seed plants had many of the traits of what are now flowering plants?
Answer: Gigantopterids