What is Radio waves: Definition and 126 Discussions

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 gigahertz (GHz) to as low as 30 hertz (Hz). At 300 GHz, the corresponding wavelength is 1 mm (shorter than a grain of rice); at 30 Hz the corresponding wavelength is 10,000 km (longer than the radius of the Earth). Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atmosphere at a close, but slightly lower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects.
Radio waves are generated artificially by transmitters and received by radio receivers, using antennas. Radio waves are very widely used in modern technology for fixed and mobile radio communication, broadcasting, radar and radio navigation systems, communications satellites, wireless computer networks and many other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the earth (ground waves), shorter waves can reflect off the ionosphere and return to earth beyond the horizon (skywaves), while much shorter wavelengths bend or diffract very little and travel on a line of sight, so their propagation distances are limited to the visual horizon.
To prevent interference between different users, the artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunications Union (ITU), which defines radio waves as "electromagnetic waves of frequencies arbitrarily lower than 3 000 GHz, propagated in space without artificial guide". The radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses.

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  1. R

    B Radio waves -- Tissue Refractive Index

    The refractive index of tissue is approx. 1.4 for light, but with with lower frequencies the refractive index decreases. What is the tissue refractive index for radio waves 1 Hz - 1 MHz?
  2. sol47739

    Am vs Fm variable capacitor receiver, what is the difference?

    What is the difference between a variable capacitor in a AM receiver and a variable capacitor in a FM receiver? I understand that Am is amplitude modulation and that the signal is carried over a changing amplitude and that the frequency is constant. And the opposite in FM signals. And a variable...
  3. J

    Understanding Destructive Interference in Radio Waves

    The solution pretends that the ship is a two point source emitter, one h above the water, and one h below the water. The one below the water is out of phase by half a wavelength. I don't understand why then d sin θ = λ - wouldn't it be d sin θ = (1/2)λ since it is out of phase? Thank you.
  4. S

    Trying to find old story: radio waves = angels carrying messages

    I wonder if anyone could help me identify a short story I read back in the 1960s. It might have been in an old (1950s) copy of Astounding Science Fiction magazine. I think the story involved a sea journey but the main thing I recall is that that radio wave communications was interpreted as...
  5. bbbl67

    I Do materials have a refractive index for radio waves?

    It's been stated that the index of refraction of materials varies with frequency throughout the EM spectrum. What are the index of refraction for various materials in the radio frequency?
  6. jaumzaum

    I Radio waves and height gain in fading zones

    Hello Guys! I'm studying radio waves and I can't understand the following: Radio waves propagates through Earths surface as a ground waves, line-of-sight waves or skywaves. There is a phenomenon that occurs with line-of-sight waves (and maybe with ground waves?) known as height gain, in which...
  7. ergospherical

    I How do submarines communicate with radio waves?

    Treating water as having a conductivity of ##\sigma \sim 5 \ \mathrm{Sm^{-1}} \gg \omega \epsilon_0 \epsilon_{\mathrm{r}}## then Maxwell ##\mathrm{III}## implies\begin{align*} \nabla \times \mathbf{H} = \sigma \mathbf{E} + \epsilon_0 \epsilon_{\mathrm{r}} \dot{\mathbf{E}} = -i \omega \epsilon_0...
  8. EnergyInMotion

    Reflection of Radio Waves by a Mirror-like surface

    Hey guys, I'm new to the physicsforums. I wanted to share some videos I made and see if anyone was interested or wanted to discuss what they see. In this video I show in a manner in which is VERY easy to see, that a reflective surface will reflect not just light but also radio waves (and most...
  9. Mircro

    Radio waves in air and water - difference in path

    Hello, this is an assigment form the 4th grade high school physics in Croatia, concerning electromagnetic waves. Radio waves of wavelength 12m propagate from the source. The source is on the surface of the water and two waves propagate from it: one through the air and the other through the...
  10. K

    Exploring the Ray Model for Radio Waves: Does it Apply to Longer Wavelengths?

    I have never seen ray model of light being considered for radio waves, or waves of larger wavelengths. I have a feeling that this model does not apply to them. Am I right?
  11. B

    Does Planck's relation apply to radio waves?

    I have some doubts about whether Planck's relation (E=hf) applies to radio waves. This has been bugging me because trying to apply Planck's relation to radio frequency results in some inconsistencies that I've been unable to resolve. BTW, I have no physics training, so please go easy on me...
  12. A

    Understanding Radio Waves & Oxygen Absorption at 60GHz

    Homework Statement: I am having difficulty understanding what exactly is happening when radio transmissions are being absorbed by oxygen at 60GHz at the atomic level. Homework Equations: Refraction/reflection, oxygen absorptions/attenuation, frequency I have tried to find the answers online...
  13. A

    Understanding Polarization-Dependent Phase Shifts of Radio Waves

    I've seen this video: There it is explained that an electromagnetic (here radio) wave has a phase shift if it was radiated in horizontal polarization, but it does not experience the phase shift when it was emitted vertically polarized when it gets reflected on the ground. When reading up on...
  14. Akshaya dhakal

    Can we see radio waves or other invisible waves with our eyes?

    There are many electromagnetic waves. Some of them are visible while other are invisible. Can we see those invisible electromagnetic waves? How Please give with scientific reason.
  15. J

    Stargazing Phase of radio waves received by a radio telescope dish

    I understand that a radio telescope can be tuned to receive radio waves generated by neutral hydrogen atoms present in galactic gas, for example, within the spirals of the milky way. I think I understand that the incoming radio waves will be a mixture of red- and blue-shifted photons depending...
  16. J

    How does a Ruhmkorf coil produce radio waves?

    Does the spark frequency = the interruptor frequency = radio signal frequency. From the sources I have found these frequencies don't seem to match. We use a 9V DC one at school. Many Thanks
  17. T

    How Can I Broadcast a Message Into Outer Space Using Radio Waves?

    Hello! I have been thinking of broadcasting a message into outer space. It sounds silly, I know, but that's just something I'd like to do for and with my niece. She's 8 years old and very interested in physics (as far as she understands it). I have some knowledge in electronics, I think I...
  18. E

    Radio waves interaction with other electromagnetic waves

    when it is asked that why radio waves do not interact with the magnetic field of electric wires or magnets, people say that radio waves are not "matter" and they do not have "charge". i really can not understand this for ex think about 2 magnets. The magnet A has a magnetic field and when we put...
  19. R

    B Effect of Varying Distance on Radio Waves

    Hello - Not sure if this is the correct location for this. I've been thinking about how a radio wave would work as the transmitter travels further away from the receiver. My example is a transmitter on a spaceship traveling 60,000 kph that transmits a loop of my favorite playlist back to...
  20. F

    Exploring How Radio Waves Make Electrons Move

    Hi! What exactly makes electrons in the antenna move to generate an induced current which then can be encoded? Is it radio waves that hits the antenna and makes the electrons move? If so, why/how? :) All I get from this link is that "the radio waves makes the electrons wiggling back and...
  21. shihab-kol

    Can the Doppler Effect Cause Changes in Radio Wave Frequency?

    I have learned that the Doppler effect causes a change in wavelength (and thus frequency) in all types of waves Suppose there is a radio station transmitting waves of frequency 90 kHz and the antennae in my car is tuned to that frequency. Then I start to accelerate and thus I am changing my...
  22. ilyasse

    Differences Between Radios & Antennas for CCNA

    hello people . i don't know if this is the right place to ask , but I'm studding for my cisco ccna and now I'm learning more about radio waves and wifi networks and i fall in love with the subject , what i don't understand is what's the difference between a radio and a antenna , because i asked...
  23. L

    Comparing Radio Waves: Short Wave vs. Phone/Radio

    Homework Statement Flat harmonic electromagnetic wave propagates in the positive direction in vacuo axis y. Vector electromagnetic energy flux density is given by: S(y,t)=Sm *cos(wt-ky)2.Wave value: k=(2*π)/λ=0.41 m-1,Amplitude Sm=26 W/m2.Compare this wave with another wave. Homework Equations...
  24. Iron_Man_123

    Which of the following is not an example of ionizing radiati

    Homework Statement Homework Equations Between Radio Waves and Protons is where my confusion lies; Online I read that Radio waves are non ionizing but if that's the answer then how are protons ionizing? I mean it's no even included in the types of ionizing radiation here...
  25. N

    I If radiowaves are reflected from objects (i.e planets)....

    ...and they can penetrate a bit in the surface, we could image the subsurface right? I do not see the problem... Help please!
  26. N

    B Can we know what exists in planets' subsurfaces?

    imagine this situation: there's a very similar planet to Earth with almost the same atmosphere and surface. we want to know what lies beyond the surface to know if life exists there. so could we send or observe radio waves or microwaves with a similar telescope as arecibo that penetrates several...
  27. GameActuator

    Can amplifiers boost radio waves for stronger signal?

    So I have basic knowledge of radio waves and how they work but how does an amplifier boost the signal? Does it just make the waves stronger (if so how) or does it effect another aspect of the radio wave? Thanks in advance for the assistance.
  28. Geek007

    Infrared rays can't be used outside for communicaiton

    Hi there, We can't use Infrared rays outside for data communication of our home as sun light also contain infrared rays which possible will interfere with it.That's what i read in Data communication book. My Question is , Does sun rays also contain radio wave, microwave ? if yes, then why can't...
  29. N

    Phase plus Antiphase radio waves

    If you produced a focused beam from, say, a cassegrain transmitter which consisted of two waves merged but one inverted what would be the result. I presume there would be destructive interference. My question is, where does the energy go?
  30. T

    What are radio waves and cosmic waves made of?

    what are cosmic waves and radio waves made of? What's the difference between the two? Can waves like them transfer energy ?
  31. T

    Relationship between an EM wave and its current

    Given the following: A directional radio wave transmitting antenna which creates a beam (diameter in mm), a current in volts, and a frequency (Hz), is it possible to calculate the em wave voltage (v/m or w/m2) immediately next to the antenna? and then at a distance of 10meters? What...
  32. kostoglotov

    A tuning fork measured by a police radar gun

    A police radar gun emits radio waves at 10.5 GHz, and measures the beats between this frequency and the returned waves to determine the speed of an object. It registers a tuning fork as "traveling" at 24.6 m/s. What is the frequency of the tuning fork. I can get the answer, but I don't...
  33. C

    Time for radio waves to reach moon?

    So I was thinking that radio waves travel at the speed of light, approximately 300,000,000 m/s.I was wondering how much time it would take if the average distance from Earth to the Moon is 384,000 km.
  34. M

    Help with radio waves and electromagnetic fields

    I need help explaining that this assumption is not correct or correct: A product uses Radio waves to turn on a LED. Radio waves can be a form of electromagnetic fields therefore, a Hall Effect sensor could be used in this device to turn on that LED.
  35. U

    What's different between a receiver & transmitter antennas?

    Hello, I'm currently working on satellite model for high-school compatition, and I'm not sure if there's a visual difference between a reciver & transmiter antenas (on satellites)... Also, is it possible to satellite to recive a radio wave information from another satellite Thank you
  36. H Smith 94

    Understanding propagation loss: What does this output mean?

    Hi there! I am currently building a simulation to model the propagation of radio waves in seawater in terms of its propagation loss. I have previously discussed the models I've looked at but have settled on a model which depends primarily on the propagation distance ##r##, the carrier wave...
  37. H Smith 94

    How is radio wave propagation modelled in seawater?

    Before I start, I apologise for the information dump that is to follow. I don't expect all questions to be answered or all models to be addressed; I simply feel it is appropriate to provide the community with my current knowledge and stage of research so you may not have to search for it...
  38. P

    MHB How Does the Phase Difference at Detector D Arise from Sources A and B?

    Sources A and B are on the horizontal x-axis and both emit a long-range radio wave of wavelength 400m, with the phase of emission from A ahead of that from source B by 90 degrees. The distance r(A) from Source A to the detector (D) in the y-axis is greater than the distance of r(B) by 100m. What...
  39. J

    Radio waves received at distance <1 wavelength

    So let's say a radio station sends out AM waves with a wavelenght of like >50m. You are standing with a receiver at a distance of <25m, what happens to the signal? Is it different or the same as if you were standing a longer distance away then 1 wavelenght? Thanks
  40. T

    Harnessing Radio Waves Project

    Alright, so for a school project that I am doing right now involves harnessing the power in the air from radio waves and the picking it up with a 75 ft of coated copper wire antenna then having the AC current go through a diode bridge to convert it to DC current and get measured. I did this...
  41. J

    Can electromagnetic waves be turned into each other?

    hey, i was wondering if this can be possible by human force, if so why are we not finding this?
  42. Lord_Segan

    Can I Calculate Satellite Dish Curvature for a Specific Radio Wavelength?

    How can I mathematically determine curvature for a satellite dish for a specific radio wavelength?
  43. psuedoben

    Astronomy: Measuring Radio Wave Distance from Universe

    when astronomers receive bursts of high energy radio waves from distant parts of the universe, how are they able to tell how far they have traveled? does it have to do with the wavelength?
  44. T

    Why don't radio waves interact with magnetic fields?

    I've been told that magnetic field does not mask or influence any GHz transmissions; TV, Radio, Wi-Fi, etc. and should not pose a problem. Can someone explain why they do not interact? Credible documentation such a law or theory? Educational documentation? Thanks in advance.
  45. S

    What particle emits the most radio waves?

    I'm operating with the understanding that everything emits radio waves (electromagnetic/light waves). Is this correct? Whatever the answer is, what particle or element or molecule emits the most/greatest radio waves?
  46. T

    Magnetic Field effect on Radio Waves (Wi-Fi Interference)

    Hello Physics Forum! I'm in desperate need of proof that magnets or magnetic field will not effect the operation or range or wireless access (Wi-Fi). I have 1/2" rare Earth magnets within a metal housing every 5' within the same area as wireless routers and the customer is concerned that it will...
  47. N

    Do we know what radio waves look like?

    A thought occurred to me In precalculus class. At the moment we are learning about sin/cos/tan/cot/sec/csc and their amplitude, periods and phases shifts. I've studied electronics on and off for about a year. I would like to know if we actually know what radio waves look like? do they actually...
  48. nuclearhead

    Radio waves from an antenna using the propagator?

    I want to find a simple example of using the Feynman propagator: 1/(|x-x'|2-(t-t')2) and also to show that no signals an travel faster than light. So I was thinking about waves emitted from an antenna. Tell me if I got this right? Assume a static source in space at x=0 and varying in time...
  49. RAHIL008

    Why Is Binary Modulation Preferred in Visible Light Communication?

    I read that for VLC, they use toggling the LEDs ON/OFF to represent binaries. Why cannot we modulate the visible light like radio waves.
  50. J

    Is electrostatics the cause of radio waves?

    That is probably a badly worded question but I understand electrostatics and I want to send simple but efficient radio signals. If I switch on a strong charge in one place it'll effect a charge away from it depending on "Coulomb's law". How is this equation expanded to explain more efficient...