7.9 Generation of Radio Waves
219
7.8 Methods for the Production of Electromagnetic Waves
As indicated above, an accelerated charge will generate an electromagnetic wave.
This charge may be a proton inside the nucleus of an atom, an electron in an atom,
an accelerating electron in a piece of metal, ions in a plasma, a charged particle in a
galactic magnetic fields, or a myriad of other possibilities. An electromagnetic wave
can also be made by flipping particles with intrinsic magnetic fields. This behavior
follows the same prediction of radiation by changing the orientation of circulating
charges, such as electrons in atomic and molecular orbits. However, one can show
that the intrinsic magnetic field of electrons and protons cannot come from internal
charge rotating, which always produces integer spin quantum numbers, rather than
the half-integer characterizing electrons and protons. 18
For each frequency range, typical production mechanisms and techniques are
summarized in Table 7.2.
7.9 Generation of Radio Waves
Radio antennae, TV transmitters, and cell phone towers all generate radio waves by
electronic circuits. They all contain resonant oscillators to generate a ‘carrier wave’
using a varying current of the appropriate frequency. This wave is modulated with an
analog or digital variation in either the frequency or amplitude of the carrier wave.
An analog modulation is considered a continuous variation of an original carrier,
while a digital modulation discontinuously changes the carrier.
The modulation of the carrier wave contains the information being transmitted,
called the ‘signal’. Transmission and reception is by antennae. To increase the range
of transmission, the signal is often amplified in a separate part of the electronic
circuitry. If the antenna is a straight wire, it is made of length about a fourth the
wavelength being transmitted or received, so that an antinode will exist where
electric energy is supplied to the circuit. Digitized signals have an advantage over
analog signals in that any intervening or intrinsic noise can more easily be separated
from the signal, and digitized information is more easily stored in packets with
addresses to individual receivers.
Electronic circuits work with currents having oscillation frequencies up to a few
tens of gigahertz, but do not work well with microwaves, because at microwave
frequencies (with wavelengths in the centimeter range), the size of the electronic
components and connections are comparable to the microwave wavelengths (in the
18 Dirac’s relativistic quantum theory predicts that electrons with half-integer spin can exist, and
will have intrinsic magnetic moments. The Dirac theory exactly predicts the value of the electron’s
magnetic moment, indicating that electrons, if they have internal structure, that structure is not yet
detectable even when probed to distances down to 10 −18 m.
219
7.8 Methods for the Production of Electromagnetic Waves
As indicated above, an accelerated charge will generate an electromagnetic wave.
This charge may be a proton inside the nucleus of an atom, an electron in an atom,
an accelerating electron in a piece of metal, ions in a plasma, a charged particle in a
galactic magnetic fields, or a myriad of other possibilities. An electromagnetic wave
can also be made by flipping particles with intrinsic magnetic fields. This behavior
follows the same prediction of radiation by changing the orientation of circulating
charges, such as electrons in atomic and molecular orbits. However, one can show
that the intrinsic magnetic field of electrons and protons cannot come from internal
charge rotating, which always produces integer spin quantum numbers, rather than
the half-integer characterizing electrons and protons. 18
For each frequency range, typical production mechanisms and techniques are
summarized in Table 7.2.
7.9 Generation of Radio Waves
Radio antennae, TV transmitters, and cell phone towers all generate radio waves by
electronic circuits. They all contain resonant oscillators to generate a ‘carrier wave’
using a varying current of the appropriate frequency. This wave is modulated with an
analog or digital variation in either the frequency or amplitude of the carrier wave.
An analog modulation is considered a continuous variation of an original carrier,
while a digital modulation discontinuously changes the carrier.
The modulation of the carrier wave contains the information being transmitted,
called the ‘signal’. Transmission and reception is by antennae. To increase the range
of transmission, the signal is often amplified in a separate part of the electronic
circuitry. If the antenna is a straight wire, it is made of length about a fourth the
wavelength being transmitted or received, so that an antinode will exist where
electric energy is supplied to the circuit. Digitized signals have an advantage over
analog signals in that any intervening or intrinsic noise can more easily be separated
from the signal, and digitized information is more easily stored in packets with
addresses to individual receivers.
Electronic circuits work with currents having oscillation frequencies up to a few
tens of gigahertz, but do not work well with microwaves, because at microwave
frequencies (with wavelengths in the centimeter range), the size of the electronic
components and connections are comparable to the microwave wavelengths (in the
18 Dirac’s relativistic quantum theory predicts that electrons with half-integer spin can exist, and
will have intrinsic magnetic moments. The Dirac theory exactly predicts the value of the electron’s
magnetic moment, indicating that electrons, if they have internal structure, that structure is not yet
detectable even when probed to distances down to 10 −18 m.