Reply To: Radio Q&A

  • Farm-Ranch-Homestead

    February 29, 2024 at 10:47 pm

    What is the radio “spectrum?”

    The radio “spectrum” is the range of frequencies that radio signals are transmitted over. These frequencies range from just above zero Hertz (cycles per second) to the Gigahertz range, in excess of 1,000,000,000 Hertz. The allocation of these frequencies is managed by the Federal Communications Commission (FCC) in the United States, and is divided up amongst the many radio services that exist today.

    Those radio services include, but are not limited to, broadcast radio and television, cell phones, military, police, fire, aviation, railroads, business, forestry, and civilian services like CB, FRS, GMRS, and Amateur (Ham) radio. All of these services (and those I didn’t mention) have designated segments of the radio spectrum assigned to them.

    For the purposes of this post, I will be focusing on the civilian services, which are available to all civilians in good standing. These services include Citizen’s Band Radio Service (CBRS), Family Radio Service (FRS), General Mobile Radio Service (GMRS), Multi-Use Radio Service (MURS), and the Amateur Radio Service, commonly referred to as “Ham” radio. Of these services, both GMRS and Amateur Radio require licensing by the FCC.

    The Citizen’s Band service operates in the range of 26.965 to 27.405 Megahertz (MHz). It is authorized for use on 40 channels, each of which has a designated frequency within the range above. Most CB radios operate on the AM mode at a maximum legal output of 4 watts. As of 2023, the FCC now allows operation on the FM mode, also with a maximum legal output of 4 watts. Another mode allowed for use on CB radio is Single Sideband (SSB), with a maximum legal output of 12 watts. CB radio is good for short distance communications of up to a few miles in favorable conditions, and occasionally at distances of several hundred to over one thousand miles when atmospheric “skip” conditions exist.

    The Family Radio Service operates in the 462 MHz and 467 MHz range. This radio service offers 22 channels within the designated frequency ranges. These channels are shared with GMRS. FRS radios are limited to a maximum of 2 watts, but may only emit ½ watt on certain channels, and the radios have a fixed (non-removable) antenna. These radios are best used for short distance communication, generally at a distance of up to a mile. Although frequently advertised as having a range of up to 20 miles or more, those distances are generally only achievable under optimal conditions, which are rare in the real world.

    The General Mobile Radio Service operates on the same 22 channels as FRS, but allows higher power operation (up to 50 watts) on some channels, as well as allowing the use of repeaters to increase range. GMRS requires users to be licensed, while FRS and CB do not. These radios are also best used for short distance communications of up to several miles, although the higher power provides greater range than FRS. With the use of a well placed repeater, GMRS can have a useful range of 20 miles or more in favorable conditions.

    The Multi-Use Radio Service operates on five channels in the 151 MHz and 154 MHz bands. Each channel has a specific assigned frequency. This service allows up to 2 watts maximum transmit power, and is best used for short distance communications of up to a few miles.

    I will explain the Amateur Radio Service, modes of operation, and several other topics in greater detail in future posts.