How do Radio Waves work when used for FM or AM Radio transmission?

Click For Summary

Discussion Overview

The discussion centers on the mechanics of radio waves used in FM and AM radio transmission, specifically how sound is encoded onto these waves. Participants explore the nature of carrier waves, modulation techniques, and the implications of frequency and wavelength in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about how sound can be encoded onto a continuous carrier wave, questioning the relationship between frequency and wavelength.
  • Another participant suggests researching superhetrodyne radio as a starting point for understanding the topic.
  • AM is defined as Amplitude Modulation and FM as Frequency Modulation, with a brief explanation of each modulation type.
  • A participant explains that AM and FM signals are not fixed frequencies but rather superpositions of the carrier frequency and additional frequencies, with specific bandwidths for AM and FM channels in the US.
  • One participant acknowledges the clarity of an explanation provided by another, indicating a preference for straightforward information.
  • Another participant elaborates on the differences between AM and FM, noting that AM modulation affects the amplitude while FM modulation affects the frequency, and mentions bandwidth considerations for FM signals.
  • A participant introduces a concept regarding the nature of frequencies, stating that pure frequency applies only to infinite constant waves and that variations in time lead to a wider frequency band.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and clarity regarding the encoding of sound onto radio waves, with some points of agreement on the definitions of AM and FM. However, there remains uncertainty and differing interpretations about the implications of modulation and frequency characteristics.

Contextual Notes

Some participants highlight the complexity of modulation schemes and the relationship between signal variations and frequency bands, indicating that further exploration of these concepts may be necessary for a complete understanding.

DCLawrence00
Messages
6
Reaction score
0
I would like to know about radio waves used for FM or AM radio. I have read many articles that say, "The sound is encoded and rides on a carrier radio wave". How is that encoded? I am under the assumption that waves just have a frequency and wavelength and that is all. If a wave is transmitted at 101 Mhz then isn't that wave just a continuous 101Mhz? How does anything get encoded onto a wave of continuous frequency? Aren't wavelength and frequency locked together so that neither can be modified without modifying the other? If that's that the case, how can anything be "encoded"?

I am lost, please help!
 
Science news on Phys.org
Start by reading about superhetrodyne radio.

FM is a different, you can do your own search for that.
 
AM = Amplitude Modulation

FM = Frequency Modulation
 
DCLawrence00 said:
How does anything get encoded onto a wave of continuous frequency?

In both AM and FM, the signal is not a fixed, pure frequency. The signal is a superposition of the carrier frequency (the one that is indicated by your AM/FM tuner) and a range of frequencies on either side. The total width of an AM "channel" in the US is 10 kHz, including guard bands between channels. FM channels are 0.2 MHz wide, again including guard bands.

In AM, the "extra" frequencies are basically a byproduct of the modulation scheme. In FM, the "extra" frequencies are the fundamental nature of the modulation scheme.
 
Thanks jtbell. Simple, clear and to the point. So many things I read refused to just say it.
 
One way to look at the difference in AM and FM is that with an AM signal the modulation is in the power (Amplitude) of the carrier wave where in FM the modulation is in the frequency. On broadcast FM, I might be off , but I believe the bandwidth used in most countries it is up to 75 kHz on either side of the carrier depending on level of audio on the signal.
 
There is one common misunderstanding about frequencies:

Pure frequency applicable only for infinite constant wave.

Otherwise, even if there is a pure sinusoid for some interval, signal still has a frequency band, which width inverse to the packet size.

This is a basic principle of information storage in the signal: More signal variations in time lead to wider frequency band.

http://en.wikipedia.org/wiki/Fourier_transformation
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 12 ·
Replies
12
Views
11K
  • · Replies 36 ·
2
Replies
36
Views
6K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 11 ·
Replies
11
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 16 ·
Replies
16
Views
25K
  • · Replies 4 ·
Replies
4
Views
3K