AM and FM in Dictionary

AM and FM, in the world of broadcasting, are acronyms that refer to two ways to modulate the carrier wave of electrical signals. AM corresponds to the acronym of ‘amplitude modulation’, while FM means ‘frequency modulated’.

AM or amplitude modulated

AM means modulated amplitude or amplitude modulation; It is a technique used in electronic communication that consists in varying the amplitude of the radio frequency carrier wave. As such, it was the first technique that was used to make radio.

The AM channel has a bandwidth that is between 10 KHz and 8 KHz. Because they are lower frequencies, whose wavelengths are greater, the range of their signal is considerably wider in relation to that of the modulated frequency.

In this sense, AM waves can measure between 100 meters (3000 KHz) and 1000 meters (300 KHz). This is the type of wave that reaches the ionosphere and bounces on it.

However, the sound quality of the modulated amplitude (AM) is well below that of the modulated frequency (FM). In addition, since they are low frequency waves, they are more vulnerable to noise, since they occur in the amplitudes of the waves. Despite this, it is the most advisable type of wave for mountainous areas.

FM or frequency modulation

FM means modulated frequency; It is a technique that allows transmitting information through a carrier wave, varying its frequency. As such, it was patented in 1933 by the American inventor Edwin Howard Armstrong.

The modulated frequency channel has a bandwidth of 200 KHz. Such a width allows the transmitted sounds (music and speech) to have greater fidelity and quality, and to be cleaner and clearer than in the modulated amplitude.

In modulated frequency, one station transmits in 101.1 MHz (that is, 101.100 KHz), and the next does it in 101.3 MHz (that is, 101.300KHz). This means that between one channel and another 200 KHz remain free. In addition, it allows to send double signal, that is, a stereo signal.

However, the range of the modulated frequency signals is less than the amplitude modulated. This is because the modulated frequency is transmitted between 88 and 108 MHz, that is, at very high frequencies, whose waves can measure between one meter (300 MHz) and ten meters (30 MHz). These types of waves, in addition, have considerably small lengths, so that they move in a straight line and quickly attenuate. Hence, it is a type of wave suitable for flat areas, where waves can be transmitted without obstacles.