How does a radio signal work?
So I understand the basics about transmitting a signal and receiving a signal. The part that I'm stuck is how we can encode voice, music, >Update:
Ya Vampire I've been looking at those terms. A lot of technical language. I guess it's tough to really understand it without seeing it. I know that a radio signal is basically an oscillating current being transmitted into space and that on top if it you need modulate the wave so that it contains a given information. If I speak my voice has a certain modulation and that modulation is superimposed onto the sine wave of the transmitter and then decoded on the other end. What I'm still unsure about is how that works. Surely my voice has a certain amplitude and frequency yet only one of those is used to modulate the radio signal. At first I thought that certain type so information require FM and certain types require AM but a normal radio can transmit voice and music using both FM and AM. Does the radio signal transmitting an amplitude modulated wave ignore the frequency of the sound that is being transmitted? Does the sound get altered as a result? I guess it'll be easiest
Comments
google the terms amplitude modulation (AM) and frequency modulation (FM). Basically in the first instance the amplitude of the signal is modulated (or varies) according to the intelligence (speech,music etc) being imparted on to it, while in the second instance the frequency of the carrier is modulated. At the receiving end, the signals are amplified and processed and the intelligence is plucked from the signal. This is very simplified and if you as an engineer are interested in the complete discussion, suggest you google the terms.
The radio signal itself is all a data stream. That is it. There is no intentional modification of the sound whichever modulation method is used.
The transmitting station will modulate the sound's audio signal onto the transmitted radio wave
The receiving station will then demodulate the radio wave into an audio signal, and then the speakers produce the sound.
An overall block-diagram would look like this:
(think of the statements in brackets as devices, think of everything else as a physical format)
Sound from the radio talent
------- [microphone] ------->
Electrical audio signal
-----[modulation circuit]---->
Electrical modulated signal combining the carrier frequency and the audio
----[transmitter]------>
RADIO WAVE
----- [receiver] ----->
Electrical signal received
------ [demodulation circuit] ---------->
Electrical audio signal
------- [audio control circuit & speakers] ----->
Sound for the listener to enjoy
Of course, the exact details of the modulator and demodulator circuits are complicated, and obviously too much for this box to explain.
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"At first I thought that certain type so information require FM and certain types require AM but a normal radio can transmit voice and music using both FM and AM"
Not true at all. The radio signal has absolutely no idea what the contents of the audio are.
AM is more primitive and cheaper to build the transmitter and cheaper to operate the transmitter.
FM is less susceptible to signal errors from background electrical equipment and naturally existing radio noise. FM signals also do not cause the audio received to loose volume upon getting farther from the transmitter.
As a result, FM is much more popular among the audience, and thus a premium to operate. But it certainly pays for itself by capturing a larger audience, and providing them with a better quality product.
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"Does the radio signal transmitting an amplitude modulated wave ignore the frequency of the sound that is being transmitted? "
You really need to take a look at the waveform diagrams to see what is going on. The deal is, the CARRIER SIGNALS (those that serve as the name for the radio station) are so much higher in frequency than human hearing, that the human hearing frequencies can be carried just by successive pieces of data.
Here is an ANALOGY for you.
Suppose you have an electric guitar that has both a whammy bar (which can tighten and loosen strings) and a volume knob (which can make the music louder and quieter).
If you just play a raw guitar string tone (suppose a 330 Hz tone) and let it ring, that is analogous to a radio transmitter transmitting SILENCE. There is no modulation in either amplitude or frequency.
To make an AM station representation, you would wiggle the volume knob. Suppose you wiggle the volume knob in 3 complete cycles per second. You've then just modulated a 3 Hz signal onto a 330 Hz carrier. This could be analogous to modulating a 6 kHz audio signal onto a 600 kHz AM radio signal. That is what AM is. In sound vocabulary, this is referred to as TREMOLO.
To make an FM station representation, you would instead wiggle the whammy bar, tightening and loosening the string. Still you use the 330 Hz carrier as the guitar string frequency, and still you wish to modulate onto it a 3 Hz signal. Instead of making the output louder and quieter like you did with AM, you make the output higher and lower in frequency. That is what FM is. In sound vocabulary, this is referred to as VIBRATO.
Your voice or most any other sound is a complex mix of many frequencies that together form a complex waveform. The only time radios or other electronics use a single (modulation) frequency is when ann engineer is testing the hardware. The microphone electrical signal is an analog of the sound pressure it is exposed to, ie the waveforms are just as complex or just as simple. They have the same frequencies.
In AM modulation, you can think of that microphone signal creating a envelope in the shape of the sound signal, or you can analyze it as a collection of radio sidebands, two (one on each side) for each sound frequency. Any modulation creates sidebands, but AM is the simplest and easiest to understand. Look for a "Oscilloscope" program for your sound card and look at the waveforms of your own voice and other sounds. If you make an Ooooh sound, it will be almost a sine wave because there are few harmonics in that sound. An A sound has much stronger hamonic frequencies so the waveform is more complicated.
http://en.wikipedia.org/wiki/Sideband
http://en.wikipedia.org/wiki/Real-time_analyzer
http://en.wikipedia.org/wiki/Single-sideband_modul...
http://en.wikipedia.org/wiki/Harmonic
In the case of AM radio, we simply increase the amplitude of the radio signal when the sound is strong and we lower the amplitude when the sound is quiet. At the receiving end we just have to detect the amplitude of the RF signal and that is the audio signal. Other types of modulation are different, but they all use variations on that theme.
At the transmitting station,sound will be converted into electromagnetic waves and transmitted and at the receiving station these electromagnetic waves will be converted back into sound waves again !
Read this...........
http://en.wikipedia.org/wiki/Radio