2006-12-21 10:39:38 · 6 answers · asked by adarba66 1 in Consumer Electronics ➔ Other - Electronics
FM or ''frequency modulation'' signals, when transmitted by a radio station's tower, tend to follow the curve of the earth there by staying close to the ground where you and i are receiving the signal. AM or ''amplitude modulation'' signals are cast out in sort of a ''sphere'' from the tower, the signal is sent in all directions and as a result is much weaker than FM. In fact most of the time when you're listening to AM radio that signal you are receiving is not directly from the tower, it's probably a ''reflected signal'', having bounced off clouds, buildings and the like. As the signal ricochets off objects it picks up unwanted ''signal noise'' we call static.
2006-12-21 10:54:32 · answer #1 · answered by Anonymous · 0⤊ 0⤋
I need to mention a couple of other things before I leave the discussion of how radio works. We've talked about AM and FM radio, but we haven't explained the real difference.
In fact, there is a lot of difference — and not just a difference in the station numbers on your radio dial.
The first type of radio service — the one we've been talking about in the last couple of modules — was AM radio.
The term modulation refers to how sound is encoded on a radio wave called a carrier wave; or, more accurately, how the sound affects the carrier wave so that the original sound can later be detected by a radio receiver.
In the top-left of this drawing the RF energy (carrier wave) is not modulated by any sound. There would be silence on your radio receiver.
Sound transmitted by an AM radio station affects the carrier wave by changing the amplitude (height) of the carrier wave, as shown on the left.
Unfortunately, this type of modulation is subject to static interference from such things as household appliances — and especially from lightening storms.
AM also limits the loud-to-soft range of sounds that can be reproduced (called dynamic range) and the high-to-low sound frequency range (called frequency response, to be explained below).
FM radio, which came along in the 1930s, uses a different approach than AM. It's virtually immune to any type of external interference, it has a greater dynamic range, and it can handle sounds of higher and lower frequencies. This is why music, with its much greater frequency range than the human voice, sounds better on FM radio.
Note on the left that when the carrier wave of FM radio is modulated with sound, that the distance between the waves, or the frequency of the carrier wave, changes.
Thus, AM radio works by changing the amplitude of the carrier wave and FM radio works by changing the frequency of the carrier wave.
2006-12-21 18:43:54 · answer #2 · answered by JoeyFine 2 · 0⤊ 0⤋
F.M. has more music channels and A.M. has more talk radio, news and sports. If you like music then f.m. is for you. But if you like news and talk radio them a.m. is for you.
2006-12-21 18:46:35 · answer #3 · answered by Trapped in a Box 6 · 0⤊ 0⤋
Radio noise looks more like an AM signal than an FM signal, so you hear the noise worse with AM. However radio noise does contain FM noise modulation components as well.
2006-12-21 18:44:06 · answer #4 · answered by bobweb 7 · 0⤊ 0⤋
AM is a lower frequency than FM which is a higher frequency - less susceptible to interference and has a shorter range.
2006-12-21 21:47:09 · answer #5 · answered by Anonymous · 0⤊ 0⤋
Because FM is broadcasted locally and AM is heard in more than one state.... sometimes nationally broadcasted.
2006-12-21 18:43:38 · answer #6 · answered by Charlene L 2 · 0⤊ 0⤋