- ?Lv 71 十年前最愛解答
Radio waves carry information by varying a combination of the amplitude, frequency and phase of the wave within a frequency band.
When EM radiation impinges upon a conductor, it couples to the conductor, travels along it, and induces an electric current on the surface of that conductor by exciting the electrons of the conducting material. This effect (the skin effect) is used in antennas. EM radiation may also cause certain molecules to absorb energy and thus to heat up; this is exploited in microwave ovens.
Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. Such frequencies and the belonging wavelength account for the following parts of the spectrum shown in the table below.
Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.
The ELF, SLF, ULF, and VLF bands overlap the AF (audio frequency) spectrum, which is approximately 20–20,000 Hz. However, sounds are transmitted by atmospheric compression and expansion, and not by electromagnetic energy.
The SHF and EHF bands are often considered to be not part of the radio spectrum and form their own microwave spectrum.
Another note of merit is that all objects have their own radio frequency, no matter how minute.
Longwave AM Radio = 150kHz - 280kHz (LF)
Mediumwave AM Radio = 530kHz - 1610kHz (MF)
TV Band I (Channels 2 - 6) = 54MHz - 88MHz (VHF)
FM Radio Band II = 88MHz - 108MHz (VHF)
TV Band III (Channels 7 - 13) = 174MHz - 216MHz (VHF)
TV Bands IV & V (Channels 14 - 69) = 470MHz - 806MHz (UHF)資料來源： From Wikipedia
- 1 十年前
無線電波是頻率介於75千赫和約10吉赫之間的電磁波，也譯作射頻(radio frequency, RF )電波，或簡稱射頻、射電。