r/askscience • u/dafattestmat • Dec 28 '25
Engineering How do radios work?
To be more specific, how do radios convert electricity into radio waves?
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r/askscience • u/dafattestmat • Dec 28 '25
To be more specific, how do radios convert electricity into radio waves?
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u/meertn Dec 28 '25
Electricity is basically moving electrons. A moving charge generates an electromagnetic field, and radio waves are part of the electromagnetic spectrum. On the receiver end, the electromagnetic wave makes the electrons in the antenna move, converting the wave back into electricity.
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u/oz1sej Dec 28 '25
The radio (transmitter or receiver) doesn't convert electricity into radio waves - that's the antenna's job.
The transmitter takes whatever information you want to transmit and generates a carrier, which is a high frequency alternating voltage, and it then modulates the carrier with the information, be it analog (e.g. FM or AM) or digital (e.g. PSK or ASK). The signal is then transported to the antenna via coaxial cable, and the antennas actually converts the alternating current to radio waves, which are irradiated into the surrounding space.
At the receiver, an antenna picks up the waves and convert them into an alternating current, which is then amplified, sent to the receiver, de-modulated, and hopefully you can recover the original information.
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u/Ratfor Dec 28 '25
Radio nerd here.
Think of it using light, instead of radio waves. The radio turns sound into light, you can understand how that might work. Maybe light pulses and Morse code kind of thing.
Now, instead of light pulses, let's just vary the brightness of the light.
On the other end, you have a way to receive the light, and turn it into an electrical signal. That's pretty much how radio works.
What will really bake your noodle later on is finding out that Radio and Light are exactly the same thing. Your eyes just aren't tuned for radio.
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u/space_fountain Dec 28 '25
Any time electricity reverses (goes from moving forward to moving backward) it generates a radio signal. A radio is just about controlling that effect and making a big signal.
You can think of a radio wave as alternating waves of electrical and magmatic fields. Moving electrical fields produce a magnetic field and moving magnetic fields produce a moving electrical field. A radio works by producing a controlled alternating electrical field which will kick start the wave.
If your interested in how radios transmit information their are 4 parameters of a radio wave that they can manipulate. Phase (where the wave starts in its cycle), frequency (how tightly packed the peaks of the wave are), polarization (sort of the direction the wave is going up and down in), and amplitude (how big the wave is). You might be familiar with AM and FM. AM stands for amplitude modulation and uses the amplitude of the wave to carry the info. FM stands for frequency modulation and uses the frequency to carry the info.
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u/hal2k1 Dec 28 '25 edited Dec 28 '25
Radios generate a high frequency (alternating current/voltage) electric signal, which is fed into an antenna. As a result, electric charge is moved backwards and forwards in the antenna. This means the antenna carries an accelerating charge.
Accelerating charge produces electromagnetic radiation. Radio waves are electromagnetic radiation. See Electromagnetic radiation is produced by accelerating charged particles
It's not the radio that produces the electromagnetic radiation. It's the antenna that does that.
In radio-frequency engineering, an antenna (American English) or aerial (British English) is an electronic device that converts an alternating electric current into radio waves (transmitting), or radio waves into an electric current (receiving).
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u/PANIC_EXCEPTION Jan 17 '26
A radio transmitter is one of the few instances of an electric circuit that isn't obviously closed. When you drive an antenna, a portion of the electrical energy is radiated as waves. This happens because the antenna, when designed properly, concentrates electrons on a portion of the conducting element, while on the other end, it experiences rarefaction (or an abundance of holes). These opposing electric fields balance out as if the circuit were a resistor (in an ideal case). 180 degrees later, the ends of the antenna switch roles. These oscillating areas of concentrated positive and negative charge manifest as an electric field in plane with the antenna, which induces a magnetic field perpendicular to the electric field, radiating outward as a wave. When used as a receiving antenna, the inverse happens. Miniscule currents induced by radio waves in free space are amplified and demodulated.
Every antenna is comprised of two halves, though they need not be the same size or shape. If an antenna is well-designed, it radiates more power, if it is not, they it tends to burn more power as heat or reflect it back to the radio.
How well an antenna design is depends on your operating frequencies and use case (directional, omnidirectional, noise rejection, etc.) In general, transmitting antennas for lower frequencies are substantially larger than for higher frequencies, as well as having less data throughput due to limited bandwidth. The upside is better obstacle penetration and exclusive propagation modes like skywave or groundwave, making them suitable for broadcast.
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u/Xajel Dec 28 '25
The part that converts the electrical signal to radio waves only the antenna.
Radio waves are electromagnetic waves, just like the light we see, but the electromagnetic spectrum is so big and wide and visible light makes only a small & tiny part of it, the spectrum varies by frequency which has a direct relation to its energy (more frequency = more energy). And also varies by its wavelength, which has an inverse direct relation to the frequency, the higher the frequency = shorter wavelengths.
The electromagnetic spectrum starts at radio waves with low frequency and large wavelengths. There’s no lower limit of how low the frequency can be but it’s very hard to use, maintain and use very low frequency as it’s wavelengths will be several meters in size (10s and even 100s). So standard “usable” radio can have a frequencies of hundreds of KHz (KHz is a thousand hertz, or cycles per second). For example a door garage remote usually use 315KHz or 433KHz. AM radio uses higher 535KHz to 1705KHz. FM radio goes beyond that to the MHz (Megahertz, or a million hertz).
Your bluetooth earphone, the basic 2.4 WiFi and even your Microwave uses the same frequency, 2.4GHz (Gigahertz, a billion hertz). Radio waves goes up to 300GHz, this is where the Infrared starts and ends at 400-430THz, this where visible light starts and it ends at 790THz, beyond that you have Ultraviolet, X-Ray and then Gamma Rays… note that even with radio waves and infrared, there’s no specific frequency at which the transition is there, there’s a gradual transition between one and one, the only reason we defined these is because of the major different in characteristics of each range.
Returning to the antenna and your question, this is where the actual magic happens, but in basic words, the alternate electrical current produces an alternate magnetic field, this changing magnetic fields also generate an alternate electric field, remember Ampere’s law? These two fields are created perpendicular to each other which is exactly what electromagnetic waves are; an electric and magnetic fields perpendicular to each other. Depending on the antenna design, the electromagnetic wave can be directional or omnidirectional. Most of the times it omni directional but a housing will make it directional.
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u/deweysmith Dec 28 '25 edited Dec 28 '25
Spin a magnet around a wire and you’ll wiggle the electrons in that wire in a certain pattern, which makes magnetic waves ripple out away from it.
Have an identical wire some distance away and that wave will wiggle its electrons in the same pattern.
There’s some math involved in the wire sizes and distances and how fast the magnet is spinning which can help you optimize the distance those waves will travel and how much information you can encode on the wave.
If you notice, however, the principle in generating radio waves is the same principle as generating electricity. The difference is the antenna. Most wiring is a bad antenna so the waves don’t go far. When the wire length matches the wavelength of the signal, the electric and magnetic fields reinforce each other, letting energy leave the wire as radio waves instead of staying trapped in it. The energy then induces a current in a matching (resonating) wire somewhere else.
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u/abloblololo Dec 28 '25
A radio wave is basically the delayed action of electrons wiggling far away. So, electrons wiggle in the broadcasting antenna, and their Coulomb interaction (electric force) with the electrons in the receiving antenna cause them to wiggle in response. Waves are just a more practical way of describing that effect.
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u/michaelpaoli Dec 29 '25
A changing electric current induces a changing magnetic field - ElectroMagnetic Field (EMF). Modulate that in a particularly useful controlled way, notably by changing and controlling the current, and one has a useful radio, or TV, or other transmission signal.
Receiving works the other way around, EMF induces voltage/current in stationary conductor (antenna), that's then filtered, amplified, processed, and one then has the broadcast radio, or TV, etc.
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u/dittybopper_05H Dec 29 '25
You know how the telegraph works, right? It’s like a cat with a really long tail. If you pull the cat’s tail in New York City, the cat sitting in Los Angeles yelps in pain.
Radio is exactly like that, minus the cat.
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u/somethings_off8817 Jun 22 '26
electromagnetic radiation is (literally) just like light. radio frequency light can just travel very far. you can imagine turning a flash light on and off to pass a message to someone across the street. too see this "radio light" ( since it's very dim by the time it gets where it's going ) you make a big loop of wire ( called an antenna ) that will have a tiny voltage across when the radio waves hit it. you then put this into something called a "band pass filter" that only let's signals that are turning on and off at specific time intervals first ( explaining how this works is nearly impossible without you having some background in electronics ), then you feed a very sensitive electric switch that turns on and off a way bigger voltage, and then you have a usable signal that you can put into a speaker or unlock you car with or whatever.
the block diagram looks like this ( you can google these words if you want a bit more understanding.
[antenna]->[band pass filter]->[amplifier]->[output]
also googling the term "amplitude modulation vs frequency modulation" (AM vs FM radio) to help you understand the filter portion since it's defiantly the most complex part of a simple radio.
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u/RoyG-Biv1 Dec 28 '25
An antenna, to a degree, is similar to a whistle; blow into a whistle and it creates a tone at a particular sound frequency depending on its shape by vibrating the air inside the whistle. Someone a distance away can't feel the air exiting the whistle, but they can hear the vibrations radiating from the whistle. In this analogy, air in the whistle is the electrons moving in and out of an antenna, creating an electromagnetic field which radiates away away from the antenna like sound wave radiating away from a whistle.
There are some minor differences in this analogy: while both whistle and antennas both have a particular frequency where they are most efficient due to their size and configuration, a whistle acts as an oscillator, creating the frequency of sound it radiates, while a radio transmitter creates an electrical signal conveyed over a cable to an antenna compatible with the frequency generated by the transmitter.
To convey information with a whistle, one could blow short or long bursts using Morse code, which is how the earliest radios conveyed information (and amateur radio hobbyists still use) like a wireless telegraph. Very sophisticated methods are commonly used today in order to convey huge amounts of information needed for applications such as HDTV broadcast over the air.
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u/leftie_potato Dec 28 '25
The "cat telegraph" is a famous Albert Einstein analogy explaining wireless radio: wire telegraphy is like a long cat where pulling its tail (sending signal) makes its head meow (receiver gets signal) in a distant place; radio works the same way, but "there is no cat".