What is FM ?

Only the amplitude changes, as the frequency remains constant the entire time.

AM radio in the Americas operates in a range of frequencies from 520 kHz to 1710 kHz. Other countries and regions have different frequency ranges.

The specific frequency is known as the carrier frequency, which is the vehicle by which the actual signal is carried from a broadcast antenna to a receiving tuner

AM radio has the advantages of transmitting over greater differences, having more stations in a given frequency range, and being easily picked up by receivers.

However, AM signals are more susceptible to noise and static interference, such as during a thunderstorm. The electricity generated by lightning produces noise spikes that are picked up by AM tuners. AM radio also has a very limited audio range, from 200 Hz to 5 kHz, which limits its usefulness more towards talk radio and less for music.

it comes to music, AM signals are of a lower sound quality than FM.

FM Radio Broadcasts

FM radio uses frequency modulation. To understand frequency modulation, consider a signal with a steady frequency and amplitude.

FM radio uses frequency modulation. To understand frequency modulation, consider a signal with a steady frequency and amplitude.

The frequency of the signal is unchanged or un-modulated, so there's no useful information contained.

once information has been introduced to this signal, the combination results in a change to the frequency, which is directly proportional to the information. When the frequency is modulated between low and high, music or voice is being transmitted by the carrier frequency.

FM radio operates in the range of 87.5 MHz to 108.0 MHz, which is a much higher range of frequencies than AM radio

The distance range for FM transmissions are more limited than AM – usually less than 100 miles.

However, FM radio is better suited for music; the higher bandwidth range of 30 Hz to 15 kHz produces the sound quality we normally prefer to listen to and enjoy.

FM broadcasts are also commonly done in stereo – a few AM stations are also able to broadcast stereo signals. And although FM signals are less susceptible to noise and interference, they can be limited by physical barriers (e.g. buildings, hills, etc.),

Radio waves are a type of electromagnetic radiation, as are microwaves, infrared radiation, X-rays and gamma-rays. The best-known use of radio waves is for communication; television, cellphones and radios all receive radio waves and convert them to mechanical vibrations in the speaker to create sound waves that can be heard.

Electromagnetic radiation is transmitted in waves or particles at different wavelengths and frequencies.

This broad range of wavelengths is known as the electromagnetic (EM) spectrum. The spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency.

The common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays

Radio waves have the longest wavelengths in the EM spectrum, according to NASA, ranging from about 1 millimeter (0.04 inches) to more than 100 kilometers (62 miles). They also have the lowest frequencies, from about 3,000 cycles per second or 3 kilohertz (kHz) up to about 300 billion hertz, or 300 gigahertz (GHz).

Scottish physicist James Clerk Maxwell, who developed a unified theory of electromagnetism in the 1870s, predicted the existence of radio waves. A few years later, Heinrich Hertz, a German physicist, applied Maxwell's theories to the production and reception of radio waves. The unit of frequency of an EM wave — one cycle per second — is named the hertz, in his honor.

Hertz used a spark gap attached to an induction coil and a separate spark gap on a receiving antenna. When waves created by the sparks of the coil transmitter were picked up by the receiving antenna, sparks would jump its gap as well.

Hertz showed in his experiments that these signals possessed all the properties of electromagnetic waves.

According to the Stanford VLF Group, the most powerful natural source of ELF/VLF waves on Earth is lightning. Waves produced by lightning strikes can bounce back and forth between the Earth and the ionosphere, so they can travel around the world.

Radio waves are also produced by artificial sources, including electrical generators, power lines, appliances and radio transmitters. ELF radio is useful because of its long range, and its ability to penetrate water and rock for communication with submarines and inside mines and caves.