AM amplitude modulation means: for example, the carrier signal is 500KHz, the amplitude is 10uA, and the acoustic wave range is 20Hz-20k Hz. The sound wave of 10uA is considered to be converted into electromagnetic wave and superimposed on the carrier amplitude. If a person emits sound waves of 600Hz, it is 10UA (carrier) +600uA=6 10uA. The resolution is 1uA.
FM FM: For example, FM carrier signal is 108MHz, and acoustic wave 1Hz is considered as 1Hz electromagnetic wave. When a person emits 600Hz, it means that the carrier signal is108 MHz+600 Hz =108.000600 MHz (this is an FM signal, the amplitude is always the same, but the frequency has changed).
Both analog and digital signals can be modulated by amplitude modulation or frequency modulation.
The digital signal is simple, and it can be modulated by AM or FM 1 and 0. 1 and 0 can be distinguished from the carrier, indicating that the signal modulation is successful.
Analog signals have many bits and low frequency. Bit width x frequency = the amount of information transmitted (low frequency can satisfy the transmission of programs).
The number of digital signals is relatively narrow (only 0 and 1), so the frequency must be high to increase the amount of data transmitted.
Under the same amplitude, the longer the wavelength of electromagnetic wave, the lower the frequency and energy, the weaker the penetration ability and the farther the propagation distance, because the diffraction ability and diffraction ability are strong.
The shorter the wavelength, the higher the frequency, the greater the energy, the stronger the penetration ability and the closer the propagation distance, because the diffraction ability and diffraction ability are very weak and can only travel in a straight line (for example, electromagnetic wave signals above 60GHz).
Hospital X-rays have short wavelength, weak diffraction and diffraction, and can only travel in a straight line, but they have strong penetration ability.
Long wave or medium wave is long and has strong diffraction and diffraction ability, which can spread to all parts of the world along the ground, but its penetration ability is weak.