An RF signal is simply an electromagnetic wave propagated into free space by some form of an antenna. RF signals have different frequencies, and by tuning a receiver to a specific frequency you can pick up a signal on that frequency if it is strong enough to be heard.

In the United States, the FCC (Federal Communications Commission) allocates different frequencies for different purposes. It also tests and licenses most services assigned to specific frequency bands. Some allocations are determined by International Treaty. The FCC then enforces these allocations.

When you listen to a ham radio repeater (for example) and the announcement says, "This is NR6CA Repeater on 442.825 MHz," what the announcement means is that you are listening to a radio transmission sending an FM signal at a frequency of 442.825 megahertz, with FCC-assigned call letters of NR6CA.

The term megahertz means "millions of cycles per second," so "442.825 megahertz" means that the transmitter at the radio station is oscillating at a frequency of 442,825,000 cycles per second. Your FM (frequency modulated) radio can tune in to that specific frequency and give you clear reception of that station. All ham UHF repeaters operate in a band of frequencies between 440 megahertz and 450 megahertz.

In the same way, AM radio is confined to a band from 535 kilohertz to 1,700 kilohertz (kilo meaning "thousands," so 535,000 to 1,700,000 cycles per second). So an AM (amplitude modulated) radio station that says, "This is AM 860 KGO" means that the radio station is broadcasting an AM radio signal at 860 kilohertz and its FCC-assigned call letters are KGO.

Common frequency bands include the following:

· AM radio - 535 kilohertz to 1.7 megahertz

· Short wave radio - bands from 1.8 megahertz to 30 megahertz

· VHF - 30 megahertz to 300 megahertz

· UHF - 300 to 3000 megahertz for channels 2 through 6

· SHF - 3000 megahertz to 12,000 megahertz

· EHF - Above 12,000 megahertz

To download a PDF file of the complete US frequency allocation click here: 104K