why the FM broadcast reciever is much better more than AM broadcast reciever?

Answer 1

By transmitting on higher frequencies, they can have more bandwidth and that translates to higher frequencies in the sound. Old AM technology, working between 550 and 1550 KHz gave a bandwidth of only about 5 KHz for audio. That means one channel, not stereo, and audio about like a telephone. FM at 88 to 108 MHz has a bandwidth of about 20KHz, on which they can put two (stereo) good quality audio channels. The only disadvantage is that FM frequencies do not benefit from atmospheric skip and are limited to perhaps a hundred miles maximum range. Old AM stations could be heard at night because of atmospheric skip across the continent. San Francisco stations were regularly heard in Alaska.

Answer 2

Zorch is on the right wavelength. Most QRN - interference from natural sources and a fair bit of QRM - man made interference has a spectrum which is similar to amplification/ amplitude modulation. That is the noise gets stronger and weaker without changing frequency much. This is similar to the signal on an AM transmission. The receiver cannot distinguish between the two so you can hear noise on an AM signal, particularly if it is weak.

An FM receiver is not very sensitive to rapid changes in signal strength at a single frequency but is designed to detect rapid changes in frequency over a small range. There is little natural or man made interference that does this.

The problem with FM is that it consumes bandwidth like there is no tomorrow. OTOH this does give a higher quality audio. Since only a small band is available (by long international agreement) on the medium wave broadcast band only a few FM stations could fit on it. So FM stations were kicked off medium wave up to the VHF regions where more bandwidth was available. This had the advantage that there is little natural noise and there is or was little man-made noise in the band.

Given greater bandwidth, an AM signal could be as good in audio quality as an FM. Likewise there is narrow bandwidth FM which has an audio quality which is lower than that of standard AM stations. This is used for communications, not entertainment.

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

Answer 3

-lesser noise interference
signal is propagated as frequencies, which external inteferences will not affect(lightning spikes affect amplitude of signals)

-lesser power required for transmission,which allows a broader transmission with the same amount of power used in AM transmission.

Answer 4

Simply less noise.