How does radio really work?

             I'm studying to take the exam for a technician class ham radio license, and have been reading up for it.  However, the book just gives practice, not theory.  For example, it says that radio energy is carried down a coaxial, window, etc. cable between the two conductors, but it doesn't say how this actually happens or works.  I know what radio does, but I'm a little lost when it comes to theory regarding its transmission, being carried in cables, filtering, SWR, etc.  Answers are appreciated.  Thanks!

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Here's how it works. Your wire antenna is receiving all sorts of radio signals, but because you are so close to a particular transmitter it doesn't really matter. The nearby signal overwhelms everything else by a factor of millions. Because you are so close to the transmitter, the antenna is also receiving lots of energy -- enough to drive an earphone! Therefore, you don't need a tuner or batteries or anything else. The diode acts as a detector for the AM signal. So you can hear the station despite the lack of a tuner and an amplifier!
(Answering from what I've seen here that I believe to be true) All I can answer is transmission. The energy that jumps off the antenna alternates from electric field to magnetic field etc. It's an alternating from of energy. When that energy jumps off that wire at a particular frequency, it will resonate (or something like that) at that frequency. The electric field generated creates a magnetic field around it. That magnetic field creates an electric field around it. Then cycle repeats until you've received the signal on the receiver. The frequency at which you transmitted must be the frequency at which you receive (everyone who operates radios already know that). For that signal to give you any sort of information, it has to be modulated. Some sort of device at the receiving end interprets the modulation as data sent over the radio and turns it into sound, light, color etc. That's the reason why that steel mesh wire on our windows (to keep the bugs out) kills off my cell signal (theoretically by draining the electric charge transmitting, or by blocking the signal because of those tiny holes that coincidentally filter out the signal thats coming from my phone like it filters out air and insects). A quick net search about Standing Wave Ratio tells me that I only understand Voltage Standing Wave Ratio, but then I don't understand what's a standing wave (physics) is in the first place!
There are 3 types of radios. 1 is a crystal set that uses just a diode, coil antenna, and variable tuning capacitor and it connected to a outdoor wire antenna and a ground rod set in the ground in the Earth. The crystal set receives only local and semi local signals depending on what antenna you use. 2 is the regenerative receiver that uses transistor or tube circuits that has a control knob that requires tuning the regeneration oscillator for best sensitvity, it's better than the crystal set. 3, is the superhetrodyne radio receiver that uses a tuning circuit, oscillator circuit, a mixer circuit, and 1 and 2nd IF then to the detector circuit to the amplifier. The AM circuit mostly uses 1N34 or 1N60 diodes, while IC's have detector circuits, the tube does not use any diode just the tube it self the diodes are inside the IC chip. When you tune a radio the coil and variable tuning capacitor works together as a tank circuit L/C and it resonates and receives the signal you want to hear, most todays circuits use PLL (phase locked loop) technology to resonate the ferrite rod coil . For FM a diode discrimator is used instead of diode.detector, mostt FM radios use transistors and silicon diodes and others use FM IC's. To receive DX you will need an antenna for AM it can be a loop antenna, ferrite rod antenna, or long wire, for FM it's a dipole or whip or yagi antenna. Wish you the best on your Ham Radio exam, I hope this helps. Study the ARRL Handbook 2010 and 2011.
Another think you might want to know is what A.M. and F.M. radio stand for: A.M. Is amplitude modulation which modifies how high/low the wave is and F.M. stands for frequency modulation which modifies how fast waves are being made. (Kind of hard to describe that without pictures.
f-156 years ago
first non of yall are right.
a satellite picks up a signal from the raidio station and the intina on your raidio picks up that signal and plays that on your raidio
No, your wrong. Satellites are used in any sort of radio except MAYBE some sort of military long distance radio. Radio towers are used. There is really no use for satellites in short range radio. It would just waste a lot of money, and make a lot more lag in your radio.
You forgot about xm satellite radio, but true.
Satellite radio still goes through a tower first lol
Marsh7 years ago
Here's another way of looking at it that may make it easier to understand.
Let's start with the most basic form of radio, the Continuous Wave, or CW. Transmitting voices, sounds and pictures over radio is a very advanced concept that require you to modulate the radio signal. There are many ways to accomplish that, so let's just look at the fundamentals for now.
You have an electric current running through a wire. The current flows in one direction at a time. Change (or oscillate) the direction of flow. Change it again. Keep changing it faster and faster. Eventually, once you reach a particular speed of oscillating the current, the energy jumps off the wire!  Let's say the frequency of this oscillation is 20,000 times per second. That would be the same as 20 KiloHertz (KHz). This is the origin and frequency of your radio signal and it fans out in all directions from the point of origin. Using an antenna you can shape the radio wave and influence it to go in one particular direction.
If you have another wire (antenna) within range of the transmitted signal, some of that energy will fall onto it and using a special detector you can hear it. The detector is nothing but an amplifier that is tuned by the use of an inductor and a capacitor so all it sees is the particular frequency you're looking for. In this example, 20 KHz.
That's Radio. Modulation of a radio signal is a whole new can of worms.
Radio waves are NOT a form of light.
Arano Marsh7 years ago
but radiowaves and light are both forms of electro-magnetic-waves
Obi-Wan14 Arano7 years ago
No, radiowaves are a form of electro-magnetic-waves but light is particles (fotons) in an wave pattern. their wavelenght decides what color they are (red blue UV ect.)
Sorry, Obi-Wan14, Arano is right. It's only a difference in frequency.
Photons are the massless, discrete particles light appers to be made up of when absorbed. But, yes, yes radio is just VERY low frequency light. Light is a meta-morph between a wave and a particle, it is NOT particles moving in a wave pattern.
Arano Obi-Wan147 years ago
hehe a foton is not a particle... fotons only exist in motion... they are quantumobjects(don't know if correct translation) which have characteristics of particles and waves...
Photons are discrete, massless, particles.
Dr.Bill Marsh7 years ago
The detector is actually a switch when used in a radio app.
The coil, tuned to ground, receives the signals through the antenna.
This sine wave signal is then sent through a diode such as a 1N34 to make the sine wave signal turn on and off.
The on and off signals are pulses that are turned into sound by the use of an earphone.
The diode is the detector. Not the coil.
We use a diode now instead of the cats wisker and galinium x-tal.
In the past all kinds of things were used as detectors.......
A rasor blade. A very tarnished quarter (.25c). Or any thing else that might have something that passes for a P/N layer.
With a crystal set it is possible, with the use of tunable tank circuits, to light and modulate an LED !
there is 2 types of radio, analogic and digital. ANALOGIC: radio transmisors create a high frequency (80 to 120 MHz) and they add to that the frequency of the audio they want to transmit. then the reciver takes of the high fequency and amplifys the audible one.
Smoke and mirrors, my friend. B)
Dr.Bill7 years ago
You need to find an "Elmer". An Elmer is usually a local ham that is willing to "Hold Your Hand" through the learning process. You will find a local radio club through the ARRL out in Connecticut. The Phone number is 1-888-277-5289 they can help you find a local club in your area where you can find an Elmer.
 radio waves are a form of light, and it's the lowest wave length on the spectrum, and like sound it can make objects resonate, like if you were to sing the exact resonant frequency of a wine glass it would start to vibrate, it's the same thing with radio, the tuner on you radio literally "tunes" the radio to resonate at a certain frequency/amplitude and whatever wave hits it at that frequency/amplitude will be picked up and turned into sound
TheZuke!7 years ago
When Albert Einstein was asked a similar question, he stated.

"A telegraph is like a very long cat, its tail is in New York and its head is in California. When you pull on the cat's tail in New York, its head yowls in California.  Radio works the same way, except there is no cat!"

Radio is an electro-magnetic wave. Lets break it down:

Electrical - electrical field
Magnetic - magnetic field

Either of these by themselves don't travel far. Electric fields can be felt as static cling, magnetic as pull between two magnets.

Electrical fields are generated by concentrating electrons, which can be stored in capacitors.

Magnetic fields are generated by electrical current, which can be stored in inductors.

This is why the inductor/capacitor, or L-C circuit, is used to create an oscillation. The energy bounces between the inductor and capacitor, alternately being stored as first a magnetic field, then and electrical field. Back and forth, that creates an electrical / magnetic undulation which can move through free space.
mad magoo (author) 7 years ago
        So, basically, couldn't radio be thought of as one big air-core transformer?  As in, The transmitting antenna is the primary coil, sending out modulated electromagnetic pulses at a set frequency, and the receiving antenna is like the secondary coil, receiving those signals through induction and then amplifying them?
 No, because magnetic induction effectively doesn't propagate through space in the same way - it doesn't RADIATE. It was originally thought that induction was usable as a distance communication method, but it doesn't work, again, the maths clearly shows why.

Really, you need to understand the concept of the near and far field to get the handle right.

Fundamentally, if you have a changing magnetic field it creates a changing electric field, which in turn creates a changing magnetic field etc etc..... the solution of the maths that shows this is in Maxwell's equations, which shows, if you can handle the very heavy mathematics, that the resulting fields move through empty space at the speed of light.

One of the best books for an empirical understanding of RF propagation I ever found is


Would make a better advert than "Fly Fishing by J R Hartley"...

Hiyadudez7 years ago

At the radio studio, the sound waves of a program go into a microphone that has electrical current running through it. These sound waves create vibrations in the current as they travel through wires to a control room.

There, technicians control their volume and send them out through a transmitter. An antenna on the transmitter sends these electrical waves out through the air as radio waves. Radio waves travel through space in all directions, just as waves of water spread out when a pebble is dropped into it.

Each radio station is assigned a particular channel, or electrical path, by the Federal Communications Commission. This channel, called the station's frequency, must be followed exactly.

You cannot see, hear, or feel radio waves in the air, but the radio in your home, which has an antenna either on the inside or outside, picks up these waves from many stations at the same time. By turning the tuning dial, you can select the station you want to listen to.

What happens is that the current in your radio tunes in to the same frequency as the radio waves sent out by the station you have chosen. An amplifier in your radio strengthens these radio waves, and the speaker changes them back into the original sound waves that went into the microphone in the studio.

Because radio waves travel at the speed of light, 186,282 miles per second, a listener in New York hears a program broadcast from California a fraction of a second before the audience in the broadcasting studio hears it!

Hope this helps!

NachoMahma7 years ago
ARRL* is a great source for radio/ham info

*American Radio Relay League