1:As per theory FM signals have infinite sidebands.Still why do these signals have a limited reception area?

Question

precise answers,websites needed

Answer 1

Theortically FM signals have infinite sidebands...but that is a property of the modulation. But what you need to worry about for reception area is the propagation. In the USA, broadcast FM operates between 88MHz and 108MHz. At these frequencies, propagation is limited to ~50mi, due to Earth's curvature. The signals are not reflected by the ionosphere, as their frequency is too high. Occasionally, you can get propagation over longer distances due to weather conditions. If temperature inversions occur, the signals can get refracted (referred to as troposheric ducting, or simply "tropo"). Also, the ionized trails of meteors reflect these signals, but that is of no help form broadcast FM... however, enterprising amateurs have used the effect to detect meteors, and thee are commercial outfits that do burst communication using reflection off of meteor trails. Of course, low power transmitters will have a shorter range. If you were to run a FM transmitter at lower frequency, say 10-30MHz (you would need to run narrow-band due to regulatory restrictions), it would propagate much further.

Answer 2

When a carrier is frequency modulated the result is a "comb-like" frequency spectrum - hence the term infinite side-bands (AM only has two). All except the lowest side-band are filtered prior to transmission to limit band-width.
This has nothing to do with the propagation of the signal which is not good for the carrier frequencies normally used in FM transmission.

Answer 3

The answers that u have are good but they missed a very critical point.With all the sidebands that are created it would be a miracle that anybody could communicate,but they have not taken into consideration the capture of the limiter. When the capture occurs at 3dB above the other signal it suppresses all other lesser signals.

Answer 4

As per theory FM signals have infinite sidebands

Answer 5

Because of the frequency used in FM (radio) they do not bend around the atmosphere (as AM signals do)

A Google search on:

"fm signal propagation"
will give you all the web info you need.

Answer 6

Radio propagation is a term used to explain how radio waves behave when they are transmitted, or are propagated from one point on the Earth to another.

In "free space", all electromagnetic waves (radio, X-rays, visual, etc) obey the inverse-square law which states that an electromagnetic wave's strength is proportional to 1/(x2), where x is the distance from the source. Doubling the distance from a transmitter means the strength is reduced to a quarter, and so on. High frequency propagation on Earth is not only affected by the inverse-square model, but by a number of other factors determined by its path from point to point. This path can be a direct line of sight path or an over-the-horizon (radio horizon) path aided by refraction in the ionosphere. Lower frequency long-distance propagation (between 30 and 3000 kHz) have the property of following the curvature of the earth (the "groundwave") in the majority of occurrences. A variety of phenomena make radio propagation more complex.

FM frequency bands (for commercial radio applications) are limited to 88.0-108.0 MHz. This effectively puts them into the VHF range, which results in line-of-sight propagation. In contrast, AM frequency bands are 520-1710kHZ (0.52-1.71MHz) ... which puts them squarely in the "groundwave" phenomena bracket.

Answer 7

Your FM system does not have infinite frequency response.