Two-Way Radio Frequencies

• Operate on many different frequencies, which often differ in different countries.
• Usually radio frequencies are preselected so that the user does not have to tune into a certain frequency, but can easily choose a frequency by pushbutton.
• In the US there is a block of 22 channels assigned to the General Mobile Radio Service and Family Radio Service.
• The selection of a frequency for a two-way radio system is affected by:
  • Government licensing and regulations
  • Local congestion or availability of frequencies
  • Terrain, since radio signals travel differently in forests and urban areas
  • The presence of noise, interference, or intermodulation
  • Sky wave interference below 50-60 MHz and troposphere bending at VHF
  • In the US, some frequencies require approval of a frequency coordination committee.
• Each country allocates radio frequencies to different two way services. In the US some examples are: Citizens Band, FRS, GMRS, MURS
• Channel numbers are used as shorthand notation for a frequency in two way radios.
• Amateur radio operators nearly always use frequencies rather than channel numbers since there is no regulatory or operating requirement for fixed channels.