What does radio am mean?

am in the radio means Amplitude Modulation, which is amplitude modulation; amplitude modulation is also commonly known as medium wave, ranging from 530-1600KHz; amplitude modulation is an electrical signal that changes the pitch of sound into amplitude; transmission The distance is relatively long, but it is greatly affected by weather factors, so it is suitable for broadcasting by inter-provincial radio stations.

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The AM on the radio is Amplitude Modulation, which is amplitude modulation. FM on the radio is Frequency Modulation, which is frequency modulation.

AM amplitude modulation (Amplitude Modulation) is amplitude modulation. AM is also commonly referred to as medium wave, ranging from 530---1600KHz. Amplitude modulation is an electrical signal that changes the pitch of a sound into an amplitude. The transmission distance is long, but it is greatly affected by weather factors, so it is suitable for broadcasting by inter-provincial radio stations. Most of the early mobile communication stations in the VHF band used amplitude modulation. Since channel fading will cause additional amplitude modulation in the analog amplitude modulation, causing distortion, it is also easy to be eavesdropped during the transmission process. It is rarely used now. Currently, it is still used in simple communication equipment. For example, the AM band in a radio is an amplitude modulated wave, and the sound quality is poor compared to the FM band frequency modulated wave.

FM (Frequency Modulation) means frequency modulation. It is customary to use FM to refer to general frequency modulation broadcasts (76-108MHz, 87-108MHz in China, and 76-90MHz in Japan). In fact, FM is also a modulation method, even between 27-30MHz in the shortwave range. As a band used for amateur radio, space, and satellite communications, frequency modulation (FM) is also used. FM radio is FM radio.

Extended information

Amplitude modulation classification:

1. Double-sideband amplitude modulation

Only in double-sideband amplitude modulation signals Contains two side frequencies, no carrier component, and its frequency bandwidth is still twice the frequency of the modulation signal.

2. Single sideband amplitude modulation

The single sideband amplitude modulation signal only contains one side frequency.

3. Vestigial Sideband Amplitude Modulation

Residual sideband amplitude modulation refers to the amplitude modulation method in which the signal transmission signal includes a complete sideband, a carrier wave and a small part of another sideband.

Basic combination method of composite frequency modulation:

1. Multi-carrier combination with independent modulators (Additive carriers with one modulator)

This combination includes two or More simple FM instruments work simultaneously, and the effect obtained is the sum of the outputs of each FM instrument (in the legend symbol abbreviation, al represents the amplitude of carrier 1, fl represents the frequency of carrier 1, and d1 represents the frequency offset of modulator 1 , that is, the amplitude of modulation body 1, f1 represents the frequency of modulation body 1, a represents the carrier amplitude, and other abbreviations in the figures are also distinguished accordingly).

2. Multi-carrier combination with only one modulator (Additive carriers with one modulator)

The effect obtained is the sum of the output of each carrier.

3. Single carrier with parallel modulators (Single carrier with parallel modulators)

4. Single carrier with multiple (step-by-step) modulators (Single carrier with serial modulators)

5. Self-modulating carrier

The so-called self-modulating carrier modulates its own frequency with the output of a signal oscillator. The oscillator's output signal is multiplied by a feedback factor (denoted fb), adding a frequency value (fm) before being re-entered into its own frequency input. The feedback factor (denoted by fb) can be viewed here as a modulation index.

Since the self-modulation processing technology always works in a 1:1 frequency ratio, a sawtooth-like waveform is always generated. The amplitude of the harmonic partial changes in proportion to the feedback factor value (fb).

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