Bands tần số điện từ B. † ITU phân chia phổ tần số vô tuyến (RF) vào tần số sau đây và các dải bước sóng trong khoảng từ 30 Hz đến 3000 GHz | 23 Appendices A. Physical Constants We use SI units throughout this text. Simple ways to convert between SI and other popular units such as Gaussian may be found in Refs. 123-126 . The Committee on Data for Science and Technology CODATA of NIST maintains the values of many physical constants 112 . The most current values can be obtained from the CODATA web site 1330 . Some commonly used constants are listed below quantity symbol value units speed of light in vacuum Co c 299 792458 ms permittivity of vacuum Co 10 12 F m permeability of vacuum Mo 4tt X IO7 H m characteristic impedance Mo Zq Q electron charge e 176462 X 10 171 c electron mass m . IO kg Boltzmann constant k X 10 77 JK-1 Avogadro constant Na L 141 994 X 1023 mob1 Planck constant h 068 76 X IO U J Hz Gravitational constant G 59 X 10 1 m3 kg 1 s 2 Earth mass M X 1024 kg Earth equatorial radius Q-e 6378 km In the table the constants c Jo are taken to be exact whereas o Mo are derived from the relationships Co - -y Mo J MoC MoC2 V Co The energy unit of electron volt eV is defined to be the work done by an electron in moving across a voltage of one volt that is 1 eV 176462 X I 0 17 c 1 V or 1 eV 176462 X 10 J 950 23. Appendices In units of eV Hz Planck s constant h is h 667 27 X 10 - eV Hz 1 eV THz that is 1 eV corresponds to a frequency of THz or a wavelength of fim. B. Electromagnetic Frequency Bands The ITTJt divides the radio frequency RF spectrum into the following frequency and wavelength bands in the range from 30 Hz to 3000 GHz RF Spectrum band designations frequency wavelength ELF Extremely Low Frequency 30-300 Hz 1-10 Mm VF Voice Frequency 300-3000 Hz 100-1000 km VLF Very Low Frequency 3-30 kHz 10-100 km LF Low Frequency 30-300 kHz 1-10 km MF Medium Frequency 300-3000 kHz 100-1000m HF High Frequency 3-30 MHz 10-100 m VHF Very High Frequency 30-300 MHz 1-10 m UHF Ultra High Frequency
