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

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.

Question: What is one piece that makes up an antenna system?
Answer: radio

Question: What is created by a portion of a radio waves energy reversing?
Answer: standing wave

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

Question: Impedance matching makes an important difference in what antenna function?
Answer: power transfer
Title: Antenna_(radio)

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.

Question: A measure of the power that is useable and the power absorbed by the terminals?
Answer: Efficiency

Question: What happens to the power that is not absorbed by the antenna?
Answer: heat

Question: What can cause that reaction?
Answer: magnetic core losses

Question: What can cause that reaction?
Answer: transmitter
Title: Antenna_(radio)

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.

Question: What would need to be placed into the transmitter to create ten W oh warmth? 
Answer: 100 W

Question: What would need to be investigated to determine how much power was radiated?
Answer: electrical measurements

Question: What factor may play a hand in lessened power from a transmitter?
Answer: impedance matching
Title: Antenna_(radio)

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.

Question: What can increase the feedpoint impedance of a component?
Answer: loss resistance

Question: The addition of Rr and Rloss equals what?
Answer: resistance

Question: What equation an determine an antennas effectiveness?
Answer: Rr / (Rr + Rloss)

Question: What is the single factor that can be precisely measured?
Answer: total resistance
Title: Antenna_(radio)

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).

Question: What is the median level for measuring atmospheric noise?
Answer: thermal noise floor

Question: In what type of programs would low efficiency antennas not make a difference in effectiveness?
Answer: receiving

Question: At lesser frequencies what can account for incorrect assumptions about efficiency?
Answer: man-made noise

Question: What is SNR?
Answer: signal to noise ratio
Title: Antenna_(radio)

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.

Question: What else is also known as power gain?
Answer: antenna gain

Question: What is used to signal toward a reciever?
Answer: transmitter

Question: Which gain does not iclude the effect of an antenna?
Answer: directive gain

Question: Wats divided by the antennas efficiency?
Answer: published gain
Title: Antenna_(radio)

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.

Question: Small and minimal frequency antennas are know to be what?
Answer: inefficient

Question: What is added to to increase ability for reception?
Answer: small loop antenna

Question: How would this antenna rate in the greater scheme of things?
Answer: little effect

Question: When talking about much larger network what effect can reduced antenna effectiveness have?
Answer: substantial cost
Title: Antenna_(radio)

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.

Question: How many polarizations will a antenna have when mounted vertically?
Answer: one

Question: What is another name for electric-field?
Answer: E-plane

Question: When is a magnetic fields right angles to a electrical field?
Answer: transverse wave

Question: Whats understood in reference of direction of an E-plane?
Answer: polarization
Title: Antenna_(radio)

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.

Question: What mostly affects polarization?
Answer: Reflections

Question: What reflector can change the waves polarization?
Answer: ionosphere

Question: What will you be matching with the  receiving antenna's polarization?
Answer: transmitter

Question: What stays the same regarding polarization state at the recieving location?
Answer: polarized transmissions

Question: What is the name used for signals recieved following reflection by the ionosphere?
Answer: a skywave
Title: Antenna_(radio)

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.

Question: Whats predictable about an antenna's geometry?
Answer: Polarization

Question: The polarization of what antenna is essential specification?
Answer: commercial antenna

Question: Most rooftop antenna's are polarized in which direction?
Answer: horizontal

Question: What is a more complicated type of polarization from an antenna's geometry?
Answer: quad antenna
Title: Antenna_(radio)

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.

Question: What are electrical fields projected on to?
Answer: imaginary plane

Question: What is the imagenary plane perpindicular to?
Answer: radio wave

Question: What is the name to describe polarization of radio waves varies over times?
Answer: elliptical

Question: How many directions does the E-plane of the radio waves oscillates back and forth?
Answer: one direction
Title: Antenna_(radio)

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.

Question: What is the best for an recieving antenna for optimum reception?
Answer: match the polarization

Question: What loses signal strength?
Answer: Intermediate matchings

Question: What is used to match vertical and horizontal linear polarizations?
Answer: circularly polarized

Question: A transmission can cause reduction in what?
Answer: signal-to-noise ratio
Title: Antenna_(radio)

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.

Question: What requires matching of the empedance to an antenna system?
Answer: Maximum power transfer

Question: Why would a transmitter have additional adjustments?
Answer: "tweak" the match

Question: What is SWR?
Answer: standing wave ratio

Question: What is the desired design value for transmmiting circuitry?
Answer: 50 ohms
Title: Antenna_(radio)

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]

Question: What can be shorter than 1/4 wavelength long?
Answer: whip antenna

Question: What is the opposite of inductive reactance?
Answer: capacitative reactance

Question: What is at the base of the antenna?
Answer: loading coil

Question: Where is the resistance seen on the loading foil?
Answer: feedpoint
Title: Antenna_(radio)

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.

Question: What is not adjustable when it comes to a transformer?
Answer: turns ratio

Question: How many ohms are in are in a standard coax?
Answer: 50 or 75

Question: A general matching network needs a minimum of how many adjustments to correct all components of impedance?
Answer: two adjustments

Question: What is included between the transmission line and the antenna element?
Answer: balun

Question: A balun should be integrated into what?
Answer: matching network
Title: Antenna_(radio)

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.

Question: What antenna's are nonresonant?
Answer: traveling wave antennas

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

Question: What are undirectional traveling wave directions terminated by?
Answer: resistor

Question: What antenna does not have linear polarization?
Answer: helical antenna

Question: What is the resistor equal to?
Answer: antenna's characteristic resistance
Title: Antenna_(radio)

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.

Question: What is the radiation patter influenced by?
Answer: dielectric constant

Question: The ground is important for what antenna?
Answer: terrestrial antenna

Question: Whats another name for the ground?
Answer: artificial ground plane

Question: What does the artificial ground plane do for the antenna current?
Answer: return connection
Title: Antenna_(radio)

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.

Question: What is the net quality of the ground dependent of?
Answer: topography

Question: What is the reason for the receiver seeing both the ral antenna and image of the antenna?
Answer: reflection

Question: What frequencies is associated with shorter wavelengths?
Answer: higher frequencies

Question: When will reflections not be coherent?
Answer: ground has irregularities
Title: Antenna_(radio)

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.

Question: What is the refractive index of the ground?
Answer: n=2

Question: When is polarized radiation reversed?
Answer: reflection

Question: What is the refractive index of air?
Answer: n=1

Question: Besides a ground, what has these phases apply well to?
Answer: electrical conductor
Title: Antenna_(radio)

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.

Question: Who proposed this theory?
Answer: Fresnel coefficients

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

Question: what is reflected and transmitted into the ground when a plane surface is struck?
Answer: electromagnetic wave

Question: What depends on the polarization and waves angle?
Answer: power remaining
Title: Antenna_(radio)

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.

Question: What is the portion of something that is reached by the radio transmission called?
Answer: aperture

Question: What effects the function of signals received by an antenna?
Answer: direction

Question: What is a measure of the power of an antenna?
Answer: microvolts

Question: How much power will be delivered to the reciever if the antenna has an effective area of 12 m/2?
Answer: 12 pW of RF power