The RF Spectrum

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 (l ) = speed of light (c ) / frequency (f ), or wavelength in metres = 300 / frequency in MHz.

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
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

As well as these narrow band applications,new networking standards such as ZigBee (Section “ZigBee (IEEE 802.15.4), p.273)” will make use of the FCC spectrum allocation for ultra wideband radio (UWB — see Section “Ultra Wideband Radio p.119 ”)that permits very low power transmission across a broad spectrum from 3.1 to 10.6 GHz.
Radio Frequency Spectrum Regulation The use of the radio frequency spectrum,in terms of the frequency bands that can be used for different licensed and unlicensed services,and the allowable transmission power levels for different signal formats,are controlled by regulatory authorities in individual countries or regions . Although there is an increasing trend towards harmonisation of spectrum regulation across countries and regions,driven by the International Telecommunications Union ’s World Radio Communication Conference, there are significant differences in spectrum allocation and other conditions such as allowable transmitter power levels which have an impact on wireless networking hardware design and interoperability.
As an example,in the 5.8 GHz ISM band used for IEEE 802.11a networks,the FCC in the USA allows a maximum transmitted power of Radio Communication Basics RF band Wireless networking specification 915/868 MHz ISM ZigBee 2.4 GHz ISM IEEE 802.11b,g, Bluetooth, ZigBee 5.8 GHz IEEE 802.11a

Radio Frequency Bands in Use for Wireless Networking
  • USA FCC Federal Communications Commission
  • Canada IC Industry Canada
  • Europe ETSI European Telecommunications Standards Institute
  • Japan ARIB Association of Radio Industries and Businesses