What is Radio signal: Definition and 23 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. DavidCummings

    I Strange radio signal from Proxima Centauri

    https://www.scientificamerican.com/article/alien-hunters-discover-mysterious-signal-from-proxima-centauri/?fbclid=IwAR0HOFRU-cvFaU66Wbqql-hoo91hA1WnCl9Azwqa84ly-zS6cjBiDFzlK8o Excerpt: Most curiously, it occupies a very narrow band of the radio spectrum: 982 megahertz, specifically, which is a...
  2. roybot

    Motion-powered GPS tracker to install permanently inside a bicycle frame

    Briefly, the problem; stolen bicycles are notoriously difficult to recover. Designing a GPS tracker to fit on one is challenging, because bicycles rarely have their own available power source. Whatever GPS unit is used must typically have its own battery as its sole source of power, which...
  3. J

    Estimation of the power in a received radio signal

    I would like to estimate the magnitude of a radio signal received from a transmitter by first principles: Transmitter antenna length ##L=1## m Transmitter antenna area ##A=1\hbox{ cm}^2## Number of electrons per unit volume in antenna ##n_e=10^{28}## Radiation resistance of antenna ##R_R=10\...
  4. S

    B From radio signal to corresponding photons

    Let's assume the following sine signal sent by a low frequency (100 kHz) transmitter. I think with the information that the sending power is 1 watt and the starting phase is 0 the signal is fully described. Are the following assumptions correct?: 1. The frequency of all photons leaving the...
  5. J

    Time for radio signal to get to a receiver

    Homework Statement A radio transmitter is located 17.5 km away. The broadcast signals travel at the speed of light (c = 3.00 x 108 m.s-1) through the air towards a radio receiver. Calculate the time it takes the radio signal to travel from the transmitter to the receiver. Homework Equations...
  6. C

    Creating a Multi-Radio Wave Demonstration: How to Find the Right Machine

    Is there a machine that can emit multiple radio waves simultaneously? I am trying to create a demonstration, but it requires multiple radio waves at once and cannot find any machines that can do so.
  7. A

    A question about radio receivers

    Could somebody explain me why it would not be sufficient for a radio receiver of an AM signal to simply consist in two elements: A very long antenna. A speaker/headphones. The set up would be as follows, the antenna is connected to the speaker and the other part of the speaker is grounded. My...
  8. H

    Receiving/transmitting with a Yagi antenna?

    Hi, I am learning about different antennas like for radio and internet wifi bandwiths and I came to the Yagi antenna. From what I understand, the people use this antenna both for receiving and emitting signal. For example, for pentesting (handshakes and all that) and for radio emitting (also...
  9. physicsEnthu_123

    Can Antenna reduce the radio signal strength when it receive

    When antenna receive the radio signal does it reduce the actual radio signal strength or strength indeed depends on the dispersion loss and other dielectric absorption? If antenna doesn’t reduce the radio signal strength(power), how it generates the current in the receiving antenna circuit? How...
  10. M

    How does an amplifier inadvertently demodulate a radio signal?

    I know sometimes speakers/amps will pick up a radio signal. I'm confused as to how the signal is demodulated accidentally. Are the signals picked up exclusively AM, or do FM signals get picked up as well?
  11. ChipY

    AM Radio signal IS sounding from my wall heater

    I am a video and sound engineer. There is clearly AM radio coming from my wall heater. An earlier thread on this topic discussed the possibilities but ultimately left the subject with an assumed crazy old lady's false perception. I assure you this is happening. There is a 50,000W AM station...
  12. V

    Radio Signal With No Resonator?

    I am a beginner at electronics, and wanted to make a simple (non-audio) radio transmitter and reciever, with no inductor-capacitor resonator, since I don't understand it and I am not making an audio radio. Here is my transmitter, with the input wire to the BJT being the signal: Here is my...
  13. C

    [Question] About the radio signal for Twin Paradox

    There is an example for the radio signal for Twin Paradox from the book "Classical Dynamics of Particle and Systems, Thornton, Marion". Refer "1.jpeg", example 14.5, it said that "However, Frank continues to receive a signal every 3 years for the 8 years it takes the last signal Mary sends when...
  14. K

    Inverting a Signal and How to make a radio signal adjustable, weak and strong

    Two Questions: 1. I am new to electrical engineering but I want to know how I would Invert a signal. By this I mean, how do I turn a weak signal from, let's say a walkie-talkie, and turn that "weakening" signal into a "strengthening" signal. I would like for the signals to be inverted, in...
  15. S

    How to locate source of radio signal?

    What method is usually used to locate exact place of radio signal source? Do exist some type of radio signals, exact place of origin which is completely impossible to locate?Well,at least up to few hundreds of feets?
  16. M

    [Mystery Solved] What household objects can pick up radio signals?

    I have just had a very strange experience, and would like to know if there is an explanation for it. There was a small tin of black olives on my kitchen work surface. I put a teaspoon into the tin, to get an olive. The moment I did this, I heard what sounded like a radio broadcast of a...
  17. S

    AM radio signal superimpostion/modulation

    Homework Statement Describe how the concept of wave superimposition is used to create AM radio waves. Homework Equations The Attempt at a Solution O.K, I am not sure that I understand how this works. In the picture attached it shows the carrier frequency inside of the audio...
  18. R

    Calculating radio signal distances

    If I know the: Frequency Effective Radiated Power Height Above Average Terrain Radiation Center Above Mean Sea Level Radiation Center Above Ground Level of a radio signal / tower, is there a way to determine the rough range of the radio signal?
  19. L

    Relativity radio signal Question

    Homework Statement A spaceship leaves Earth at 12 noon. At that time the spaceship clock is set to be synchronised with Earth time. It travels through space in a straight line at a constant speed 0⋅60 c. A radio signal is sent to the spaceship from Earth at 2pm. A shuttle is launched from...
  20. P

    2.4GHz radio signal through small gaps

    For an engineering project I am trying to place a 2.4GHz RFID tag inside a resin casting of a large seaside pebble. However since the resin is less dense than a real pebble, I need to add some mass of metal (since is is much denser) to the resin before it sets. It is crucial for the casting to...
  21. S

    Wavelength of carrier frequency radio signal

    Homework Statement Your favorite radio FM radio station broadcasts at a carrier frequency of 94.7 Megahertz. What is the wavelength of the carrier frequency radio signal? Homework Equations velocity=wavelength(frequency) The Attempt at a Solution 94.7x10^-6(w)= 3x10^8 w= 3.2...
  22. C

    Spacecraft Traveling Past Space Station: Length and Radio Signal Timing

    A spacecraft (Lo = 80 m) travels past a space station at speed 0.7c. Its radio receiver is on the tip of its nose. The space station sends a radio signal the instant the tail of the spacecraft passes the space station. (a) What is the length of the spacecraft in the reference frame...
  23. M

    How is a radio signal turned into an image?

    Im not talking about TVs, but radio astronomy. We receive signals from say a distant star and turn it into a picture, but how?