AM radio waves

Examples of AM radio waves in the following topics:

• Radio Waves

  • Radio waves have many uses—the category is divided into many subcategories, including microwaves and electromagnetic waves used for AM and FM radio, cellular telephones and TV.
  • AM radio waves are used to carry commercial radio signals in the frequency range from 540 to 1600 kHz .
  • The abbreviation AM stands for amplitude modulation—the method for placing information on these waves.
  • FM radio is inherently less subject to noise from stray radio sources than AM radio because amplitudes of waves add noise.
  • Amplitude modulation for AM radio.

• The Production of Electromagnetic Waves

  • Electromagnetic waves are the combination of electric and magnetic field waves produced by moving charges.
  • Electromagnetic waves are ubiquitous in nature (i.e., light) and used in modern technology—AM and FM radio, cordless and cellular phones, garage door openers, wireless networks, radar, microwave ovens, etc.
  • Placing a coin in contact with both terminals of a 9-volt battery produces electromagnetic waves that can be detected by bringing the antenna of a radio (tuned to a static-producing station) within a few inches of the point of contact.
  • Electromagnetic waves are a self-propagating transverse wave of oscillating electric and magnetic fields.
  • Notice that the electric and magnetic field waves are in phase.

• Antennae

  • An antenna is a device that converts electric power into radio waves, and vice versa.
  • As a consequence, visible light and radio waves should share common characteristics.
  • An antenna (or aerial) is an electrical device that converts electric power into radio waves, and vice versa.
  • In transmission, a radio transmitter supplies an oscillating radio frequency electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves).
  • These serve to direct the radio waves into a beam or other desired radiation pattern.

• Diffraction

  • Diffraction refers to various phenomena such as the bending of waves around obstacles and the spreading out of waves past small openings.
  • Diffraction refers to various phenomena which occur when a wave encounters an obstacle.
  • In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings.
  • Similar effects occur when a light wave travels through a medium with a varying refractive index, or a sound wave travels through one with varying acoustic impedance.
  • Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, X-rays and radio waves.

• Interference

  • Interference occurs when multiple waves interact with each other, and is a change in amplitude caused by several waves meeting.
  • Unlike solid objects, two waves can share a point in space.
  • In physics, interference is a phenomenon in which two waves (passing through the same point) superimpose to form a resultant wave of greater or lower amplitude.
  • The effects of interference can be observed with all types of waves, for example, light, radio, acoustic and surface water waves .
  • In constructive interference, the two amplitudes of the waves add together and result in a higher displacement than would have been the case if there were only one wave.

• Microwaves

  • The microwave region of the electromagnetic (EM) spectrum is generally considered to overlap with the highest frequency (shortest wavelength) radio waves.
  • It indicates that microwaves are "small" because have shorter wavelengths as compared to waves used in typical radio broadcasting.
  • The boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary.
  • This band is commonly used in radio astronomy and remote sensing.
  • Microwaves overlap with the high frequency portion of the radio section of the EM spectrum.

• Maxwell's Predictions and Hertz' Confirmation

  • Maxwell's prediction of the electromagnetic force was confirmed by Hertz who generated and detected electromagnetic waves.
  • This means Maxwell's equations predicted that radio and x-ray waves existed, even though they hadn't actually been discovered yet.
  • Across the laboratory, Hertz had another loop attached to another RLC circuit, which could be tuned (as the dial on a radio) to the same resonant frequency as the first and could, thus, be made to receive electromagnetic waves.
  • The propogation of an electromagnetic wave as predicted by Maxwell and confirmed by Hertz.
  • The apparatus used by Hertz in 1887 to generate and detect electromagnetic waves.

• Wireless Communication

  • These wireless phones use radio waves to enable their users to make phone calls from many locations worldwide.
  • The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g., radio transmitters and receivers, remote controls, etc.) that use some form of energy (e.g., radio waves, acoustic energy, etc.) to transfer information without the use of wires.
  • With infra-red waves, distances are short (such as a few meters for television remote control) while radio waves can reach as far as thousands or even millions of kilometers for deep-space radio communications.
  • Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television, and cordless telephones.
  • These wireless devices use radio waves to enable their users to make phone calls from many locations worldwide.

• Doppler Effect

  • We have a radio transmitter in the primed frame radiating at a frequency $\omega'$.
  • The time between the arrival for two crests of the wave in the unprimed frame is given by,

• Photon Energies of the EM Spectrum

  • Maxwell's equations predicted an infinite number of frequencies of electromagnetic waves, all traveling at the speed of light.
  • Maxwell's predicted waves included waves at very low frequencies compared to infrared, which in theory might be created by oscillating charges in an ordinary electrical circuit of a certain type.
  • In 1886, the physicist Hertz built an apparatus to generate and detect what are now called radio waves, in an attempt to prove Maxwell's equations and detect such low-frequency electromagnetic radiation.
  • Hertz found the waves and was able to infer (by measuring their wavelength and multiplying it by their frequency) that they traveled at the speed of light.
  • Generally, electromagnetic radiation is classified by wavelength into radio waves, microwaves, terahertz (or sub-millimeter) radiation, infrared, the visible region humans perceive as light, ultraviolet, X-rays, and gamma rays.