Why AM signal reaches over a wide range of distance but why not FM signal?

Answer 1

All radio signals travel just beyond the horizon if they are not absorbed or blocked. Lower frequency signals (below the MUF(Maximum Useable Frequency)) are reflected off the earth's ionosphere and travel back down to earth well beyond the horizon. This may repeat to allow signals to travel around the world. Most commercial FM signals frequencies are higher than the MUF and just travel into space. Meteors and weather events can reflect or duct high frequency signals beyond the horizon on occasion.

Answer 2

The frequency of AM radio is from 0.55 MHz up to 1.60 MHz. The frequency of FM radio is from 88 MHz up to 108 MHz. The two different frequency bands propagate over the Earth in different ways. AM radio travels by 'ground wave'; the radio waves hug the ground and follow the curvature of the Earth over the horizon, so an AM receiver can hear a signal from an AM transmitter that is located relatively far away. In addtion, at night, the ionosphere is thicker and stronger, and this high altitude atmospheric layer acts like a mirror to radio waves in the AM band. So, AM stations can be heard over especially large distances at night. FM signals, at the much higher frequencies of around 100 MHz, propagate only by "line of sight", which means if the transmitter is not visible directly by the receiver, the signal cannot be picked up. This also is the case for broadcast TV signals. That's why FM and TV transmitters tend to be put on hilltops or mountain peaks, or in flat lands, on tall towers or buildings. This gives greater line of sight distance for receivers for these signals. So it has nothing to do with the modulation method (amplitude or frequency modulation). It has to do with the physics of radio propagation over the ground and through the sky.

Answer 3

The difference is frequency.

FM is high frequency (apx 100 MHz) and is 'line of sight' only, at least under normal atmospheric conditions. However, sunspots can sometimes trigger rare events making reception of FM signals over distances of 1000 miles or more possible.

AM is low frequency (apx 1 MHz) and the longer wavelength will bend around the curve of the Earth, often going most of the way around the world. Ironically, solar radiation disrupts this effect, which is why AM stations are best received at night.

Answer 4

AM frequencies have a longer wavelength allowing it to bend around large objects such as buildings and mountains and continuing on its path. an FM frequency is much shorter and simply bounces off those objects and not move around them. Because of the higher frequency though, an FM signal is more clear than an AM.

Answer 5

You can't bend a wave (without a large gravity force) but AM waves do bounce off the middle atmosphere where FM has higher energy and passes right through

Answer 6

Here u can get ur answer if u hav knowledge of shortwaves. Bcoz of this shortwave fundda am goes farther than FM. Most of the answers given above are good but they donot describr the phenomenon completely

Answer 7

That's how the channels are designed. I'm not expert, but FM is local, AM is further reaching.

Answer 8

Waves do bend. The most common causes of bending wave are refraction, reflection and diffraction.