Radio Waves as Photons

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KW4UP, Oct 9, 2017.

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  1. KW4UP

    KW4UP Ham Member QRZ Page

    Dear reader, please keep in mind that photons and electrons at different frequencies exhibit varying degrees of magnetism, induction, field effects and susceptibility to those forces. Some of the terminology utilized herein may be presented in other literature with different connotations. I appreciate your flexibility with my usage of the terminology presented.

    Radio signal radiation is a product of alternating current between electrically coupled conductors within an induction field. The induction field is enhanced by conductor proximity and frequency resonance. As a transmitter energizes a conductor* the electron shells of the conductor's atoms alternate between high and low energy states. Photons are emitted on each fall of the electron shell energy state which peaks on both halves of the radio frequency cycle (from the top of the sine wave peak back towards zero as well as the negative peak return back towards zero). This phenomena is exactly the same as photon generation in fluorescent lighting utilizing the excitation of mercury atoms between higher and lower energy states to produce visible light.

    Radio waves are photonic and not electronic, no electrons travel through free space outside of the antenna's induction field and even then the term "free" infers plasma in its purest state and well above the energy levels that are likely to exist in the circumstances Of this discussion. The electrical current between an antenna's conducting elements is a closed loop, electrons are not the medium by which radio signals propagate. The closed current loop facilitates the excitation of atoms and the subsequent production of photons. Much like the two support wires of an incandescent light bulb deliver power to the filament that produces photons in the human visible spectrum, the conductors of an antenna facilitate the electron flow that produces photons at radio frequencies. Within this analogy the bulb filament is equivalent to the induction field between the two antenna conductors.

    Just like the light emitted from an incandescent bulb, radio waves are not influenced by the path of the electrons in the antenna circuit, radio waves radiate outward from the antenna elements based solely on the element's geometric orientation.

    Another analogy is a needle, heated to incandescence by a blowtorch, produces light that is unaffected by the physical flame.

    When radio waves come into the charge field of loosely bound electrons typical of metallic conductors, photons are absorbed and drive the electrons into a higher energy state. This action induces voltage changes within the receiving conductor and those changes are detected and amplified.

    Keep in mind that the mechanism by which photons are emitted and absorbed by electrons is not known at this time, however the effects of the phenomena itself is well known. Those desiring to confirm the veracity of these statements need only to check online by searching, "Radio waves are photons.

    Thoughts, comments, corrections or hysterical laughter?
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  2. W5DXP

    W5DXP Ham Member QRZ Page

    From QED by Feynman:
    "So now, I present to you the three basic actions, from which all the phenomena of light (including RF) and electrons arise.
    - Action #1: A photon goes from place to place.
    - Action #2: An electron goes from place to place.
    - Action #3: An electron emits or absorbs a photon."
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  3. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    In my book "Propagation and Radio Science" I have a chapter, "Walking the Planck," which describes why, at HF frequencies, photons are essentially non-existent. Although you COULD define HF radiation in terms of photons, Planck's Constant is going to guarantee that the quantities are minuscule....and non-measurable.
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  4. KW4TI

    KW4TI Ham Member QRZ Page

    Ok, I am going to take a shot at explaining why the photon nature of electromagnetic fields is generally unimportant at radio frequencies and classical behavior dominates. However this is not always the case, an exception being the discrete nature of microwave photons in superconducting junctions like Josephson junctions.

    The energy of a photon is proportional to its frequency. Energy = Planck's constant X frequency. The frequency of a visible light photon, for example green light, is about 600 THz. The frequency of a microwave is about 1 GHz, or 600,000 times less. Planck's constant is 6.62 X 10^-34 J/Hz, so a single green photon has an energy of about 4 X 10^-19 J, and the microwave photon is 6.6 X 10^-25 J. These are very small amounts of energy. It is easier to talk about electron volts (eV), or the energy required to move an electron up a potential of 1 volt. In this case, the green photon is 2.5 eV, while the microwave photon is 4 micro-eV = 0.000004 eV.

    Now the important question is: when we are detecting a signal, how many photons are available to detect? The amount of power in the signal to be detected is important, as well as the power in the noise. The noise is determined by the thermal fluctuations at the detector, and the thermal fluctuations depend on the temperature of the detector. The energy of fluctuations in a single "mode" or available receiving state is given by Boltzmann's constant k=8.617X10^-5 eV/K, times the absolute temperature, which at room temperature is about T=300 kelvins. The "fluctuation energy" is kT = 26 milli-eV = 0.026 eV. The energy of the green photon, 2.4 eV, is much bigger than the fluctuation energy, so that there will be very few fluctuations at the energy of the green photon. However at the energy of the microwave photon (0.000004 eV is much less than 0.026 eV), there will be many thermally generated photons, and in the detector this is "Johnson noise" or broadband white noise or "static." The thermal noise obscures the discrete detection of the microwave photon. If however, the temperature is cooled a small fraction above absolute zero, the discrete nature of the microwave photon can be observed in something like a superconducting quantum interference device (SQUID).

    For a given amount of power, there are comparatively fewer photons emitted from a green source of light than a microwave antenna because the energy of the green photon is much greater than the microwave photon. In addition, the wavelength of the green light is much shorter (500 nm or 0.5 millionths of a meter) than the 30 cm wavelength of the microwave photon. If you imagine a cube 1 meter on a side, approximately 37 cubic wavelengths of microwave photons fit in the box, but 8 X 10^18 cubic wavelengths of green light fit in the box. If we try to localize a photon in the box, there are just many many more possible locations for the green photons, and there are fewer green photons to begin with. Therefore it is overwhelming likely if we find a green photon, they will be sparsely placed and infrequently interact with a detector. Microwave photons, being much more numerous, and only in relatively few locations, are much more likely to interact in large quantities with an antenna placed in the box. Because radio waves have much longer wavelengths and much smaller energies, an antenna is likely to interact with numerous radio photons, and when the antenna does, the thermal noise generated in the antenna is going to obscure the quantum nature of the radio photon. Only if an exquisitely sensitive experiment is performed at low temperature can the quantum nature of the radio photon can be detected. On the other hand, a device like a photomultiplier tube can easily resolve individual photon arrivals of green light.

    I hope that helps explain a bit why the quantum nature of radio photons can be generally ignored in almost all cases.


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  5. N0TZU

    N0TZU Premium Subscriber QRZ Page

    I missed the point of the OP. Is he asking for a critique of what he posted? Or just trying to tell us how photons are related to radio?

    It's far more useful to describe radio in classical terms rather than quantum terms with photons. However they are both valid descriptions. At much higher frequencies (=higher energy photons) like light, X rays, etc, the quantum description is very useful and explains phenomena like the photoelectric effect that the classical description can't.
  6. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    I would modify that statement. The RAY is merely a mathematical construct, in the same vein as magnetic "field lines." However the wave nature of radio is very real and certainly appropriate as a model.

    Again, I would reiterate and abet what others have said here, that Planck's constant is so huge (or so small, depending on your point of view) that expressing "normal" radio waves in terms of photons is impractical at best.

    NONE of our familiar physics models are complete in themselves, but that does not diminish their usefulness in the least. The wave/particle duality of matter does not invalidate either one or the other. Both work and both are useful for solving different problems.
  7. N0TZU

    N0TZU Premium Subscriber QRZ Page


    Electromagnetic waves and photons describe the same thing. They are duals of each other. Photons are the quantized particle representation of an EM wave, and vice versa. So when your radio transmits, it is creating an electromagnetic wave which is equivalent to photons.

    Light is an electromagnetic wave, or photons, same as radio, but at a much higher frequency. Green light is roughly 500 nanometers in wavelength which is about 600 terahertz.

    As for the details and math to prove this, it's a little complicated. It took the best physicists of the early 20th century to work it out. There are plenty of references on the Internet and elsewhere about the wave-particle duality if you want to do more research.
    Last edited: Oct 10, 2017
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  8. N0TZU

    N0TZU Premium Subscriber QRZ Page

    Please do.
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  9. W5DXP

    W5DXP Ham Member QRZ Page

  10. N1UV

    N1UV Subscriber QRZ Page
    Geez. Any undergrad student who's completed a quantum mechanics 101 class knows this. Ever heard of the Planck- Einstein equation of E=hf where the energy of a photon is proportional to its frequency (h=Plancks constant). The frequency is not limited to light or above. Please read a highly simplified explanation of the topic here
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