How does Amplitude Modulation acutally work with the two side bands and carrier?

Question

Why are different frequencies needed above and below the carrier frequency? Why can't a sound signal simply be sent over one frequency (the carrier). What is the purpose of the carrier anyways?

I'm assuming people that are interested in space know everything about radio waves.

There is no category for amateur radio questions.

So then does the frequency furthest away from the carrier represent the highest pitch of sound and the frequency closest to the carrier represents the lowest sound pitch?

Answer 1

This question is totally off topic for the area you placed it in, Astronomy & Space. Your chances of getting an answer will be much better if you place it in the right area.

Answer 2

As usual too much information in answers that are not strictly true.
The carrier is a radio wave that can be transmitted to a remote receiver. Frequencies below 200kHz have very low distance capability.
In AM modulation the Amplitude of the carrier is varied (Modulated) by the amplitude of the signal. The signal is usually a band of audio frequencies that make up the audio spectrum you wish to transmit.
The side bands are just an annoyance to AM transmissions and some old military and amateur transmissions used suppressed side band transmission.
The only place side band is useful is to narrow the bandwidth of the transmitted signal to increase signal to noise ratio,( SSB transmission)

Answer 3

Answers are anywhere you seek - AM radio transmissions use a "carrier" signal because the audio cant be sent by itself. As you know radio waves vary in length and amplitude. So to transmit (xmit) a signal, the audio is piggybacked as sidebands and central band to the carrier. The amount of signal varies as the audio varies, the carrier being steady at the radiated output power.

In amatuer and CB radio xmissions (remember above?) you have a carrier and 2 side bands. CB uses the three all at the same power (legal) of 4 watts. Switching to sideband where you send one channel only with the carrier you have three separate 4 watt signals giving you 12 watts output.

Answer 4

Okay...

In viewing the way a transmitter works, you must realize that some form of frequency determining circuit must be used to place the RF Signal at your desired spot in the frequency spectrum. The spectrum (or range of possible frequencies) will depend upon the design of your particular fadio set. Some work on a range of frequencies from 0.5 to 1.75 Megahertz (the AM Broadcast Band), some work on a range
of frequencies from 1.6 Megahertz to 30.0 Megahertz (the MF and HF Bands), and others work on:
30.0 - 54.0 Megahertz (Low Band VHF)
54.0 - 108.0 Megahertz (Low Channel Television,
& FM Broadcast Band 88.0 - 108 Mhz)
108 - 135 Megahertz (AM Aircraft Band)
etc., etc., etc.

You need to position your transmitted signal somewhere in
the appropriate range of frequencies where people will expect to tune in and receive what you are sending. The device that does that frequency setting is called an oscillator.
Many types of oscillators exist, fixed frequency oscillators,
variable frequency oscillators, synthesized oscillators, etc.
All of them do one thing...they output an RF Signal on one particular frequency. If you amplified that signal and sent it through a tuner out to an antena it would be a constant carrier signal.

Now The object of transmitting a signal is normally to convey some kind of information to a distant point where it will be received and the information retrieved by a listener who has an appropriate receiver. A constant carrier signal can only signal "the ON Condition." It just sits there and goes Blahhhhhhhhhhhhhhhhhhhh... or Beeeeeeeeeeeeeeee...

Using a keyer, you could interrupt the carrier signal and send a prearranged kind of code like in Morse Code using long and short key down pulses from the transmitter. At the far end someone who knows what particular code you are sending could decypher your transmission and hand the information to the designated recipient. Voila, working code transmitter and receiver set up.

However, not everyone knows the code, and if you want the transmission to be heard and understood by the masses of people out there in radio land, you probably ought to send your transmission using Voice.

To do that, you use some form of microphone, and audio amplifier to influence the current going into the final RF Amplifier in the transmitter. As you speak into the mike, the audio amplifier's power is added and subtracted to the normal current flow of the RF AMplifier and this results in added energy on the carrier frequency which is called side bands. If you speak, the side bands show an energy burst higher and lower than the center frequency (which is the carrier). Depending upon the exact method (circuitry) of adding the audio to the carrier transmitter there may or may not be additional fluctuations in power of the actual carrier signal also as you speak into the mike.

At the distant receiving location, a special Demodulator circuit strips the audio off of the incoming carrier signal and sends it to an amplifier and speaker for people to listen to audibly. There are many types of Demodulators that perform this function.

As it happens, the information content in the Upper Side Band is the same as the information contained in the Lower Side Band. So, in the interests of using as little frequency spectrum as possible, many modern transmitters use special circuitry to suppress one or the other of the two sidebands, and even the carrier. The result is that all of the power that is generated gets dumped onto the remaining side band and a very potent and narrow transmitted signal results. This is called Single Sideband. Many, many more of those signals can be packed into a given chunk of frequency bandwidth than signals with the standard carrier and two side bands.

Hope this helped you understand Side Bands better...

Zah

Answer 5

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Answer 6

In AM, the amplitude of the carrier wave is varied with the information.
This generates the sidebands.
If there was no sidebands there would be no information.
The Carrier is 'literally' the carrier of the sidebands, though it can be suppressed and one sideband removed (i.e. as in single sideband).
Look up modulation in a decent radio reference book.