ectrum The radio frequency, or RF, communication at the heart of most wireless networking operates on the same basic principles as everyday radio and TV signals. The RF section of the electromagnetic spectrum lies between the frequencies of 9 kHz and 300 GHz (Table 4-1), and different bands in the spectrum are used to deliver different services. Recalling that the wavelength and frequency of electromagnetic radiation are related via the speed of light, SO that wavelength (A) = speed of light (c) / frequency (f), or wavelength in metres = 300 / frequency in MHz. Table 4-1: Subdivision of the Radio Frequency Spectrum Transmission type Frequency Wavelength Very low frequency (VLF) 9-30 kHz 33-10 km Low frequency (LF) 30-300 kHz 10-1 km Medium frequency (MF) 300-3000 kHz 1000-100 m High frequency (HF) 3-30 MHz 100-10 m Very high frequency (VHF) 30-300 MHz 10-1 m Ultra high frequency (UHF) 300-3000 MHz 1000-100 mm Super high frequency (SHF) 3-30 GHz 100-10 mm Extremely high frequency (EHF) 30-300 GHz 10-1 mm Chapter Four Beyond the extremely high frequency (EHF) limit of the RF spectrum lies the infrared region, with wavelengths in the tens of micrometre range and frequencies in the region of 30 THz (30,000 GHz). Virtually every Hz of the RF spectrum is allocated for one use or another (Figure 4-1), ranging from radio astronomy to forestry conservation, and some RF bands have been designated for unlicensed transmissions. The RF bands which are used for most wireless networking are the unlicensed ISM or Instrument, Scientific and Medical bands, of which the three most important lie at 915 MHz (868 MHz in Europe), 2.4 GHz and Space Space Earth Fixed Mobile Research Operation Exploration Space Research Fixed Mobile Amateur Broadcasting Satellite Mobile Radio Location Amateur Fixed Mobile Radiodetermination Satellite Mobile Satellite Broadcasting Fixed Satellite Earth Radio Space Astronomy Research Exploration Satellite Aeronautical Meteorological Radionavigation Radio Location 2.9GHz Figure 4-1: FCC Spectrum Allocation A