What does AM mean in Chinese? Thank you.

If it is time, of course, it is morning and afternoon is PM.

But there are others:

What is AM/FM?

What bands of radio waves are used in radio broadcasting and television? How do they spread?

At present, AM radio broadcasting is divided into three bands: long wave, medium wave and short wave, and the signals are transmitted by radio waves in the corresponding bands.

Radio broadcasting in China has only two major bands: medium wave and short wave. The frequency band used in medium wave broadcasting is roughly 550kHz- 1600kHz, which is dominated by ground wave propagation with some sky waves; The frequency band used in short-wave broadcasting is about 2MHz-24MHz, which is dominated by sky waves and accompanied by ground waves at close range.

Most FM broadcasts use VHF radio waves to transmit signals, with a frequency of about 88MHz- 108MHz, and mainly rely on space waves to transmit signals.

At present, terrestrial radio and television is divided into VHF (very high frequency or meter wave) and UHF (ultra high frequency or meter wave) two frequency bands. In China, the frequency range of VHF TV is 48.5MHz-3MHz, divided into 1- 12 channels, and the frequency range of UHF TV is 470MHz-956MHz, divided into 3-68 channels. They are basically propagated by space waves. There are six frequency bands of satellite radio and television in the world, and the main frequency band is 12 GHz, which is also spread by space waves.

What is AM/FM? What is FM wave?

The modulation method that makes the carrier amplitude change according to the modulation signal is called amplitude modulation. AM radio waves are called AM waves. It maintains the frequency characteristics of the high frequency carrier, but the shape of the envelope is similar to the signal waveform. The amplitude of amplitude modulated wave is determined by the intensity of modulated signal. AM waves are represented by the English letter AM.

The modulation method that makes the carrier frequency change according to the modulation signal is called frequency modulation. The frequency variation amplitude of the modulated wave is determined by the amplitude of the modulated signal, and the variation period is determined by the frequency of the modulated signal. The amplitude of the modulated wave remains unchanged. The waveform of FM wave is like a spring that is unevenly compressed. FM waves are represented by the English letter FM.

What is the sending and receiving process of radio communication?

Radio programs are broadcast on radio stations. The sound waves of broadcast programs are converted into audio signals by electro-acoustic devices, which are amplified by audio amplifiers, and oscillators generate high-frequency equal-amplitude oscillation signals; The modulator modulates a high-frequency constant-amplitude oscillation signal with an audio signal; The modulated high-frequency oscillation signal is amplified and sent to the transmission line, converted into radio waves and radiated.

The reception of radio broadcast is realized by radio. The receiving line of the radio receives the radio waves in the air; The tuning circuit selects the signal with the required frequency; The detector restores the high-frequency signal to an audio signal (i.e. demodulation); Amplifying the demodulated audio signal to obtain sufficient driving power; Finally, the broadcast content is restored through electro-acoustic conversion.

To sum up, the transmission and reception of radio communication (broadcasting also belongs to the category of radio communication) can be summarized as three mutually opposite conversion processes, namely, transmission information-low-frequency signal, low-frequency signal-high-frequency signal and high-frequency signal-electromagnetic wave.