RF (radio frequency) is a type of radiation. Other types of radiation are sunlight, infrared (like a TV remote control), ultraviolet light (the UV rays from the sun), x-rays, and things called "alpha, beta and gamma particles" that might come from an atomic bomb, and cosmic rays (radiation that is still floating around from the Big Bang when the universe was created). Some of these types of radiation have a low frequency, some of them are very high.

All these frequencies can be measured and put in a graph called the EM spectrum.

Some of these frequencies are not too far away from what you can tune into on your car stereo.

There are only a couple of these that most amateurs are going to be interested in. These are highlighted below:

• ELF - Extremely Low Frequency
• SLF - Super Low Frequency
• VF / ULF - Voice Frequency / Ultra Low Frequency
• VLF - Very Low Frequency
• LF - Low Frequency
• MF - Middle Frequency
• HF - High Frequency
• VHF - Very Higher Frequency
• UHF - Ultra High Frequency
• SHF - Super High Frequency
• EHF - Extremely High Frequency

Most car radios cover part of the MF range. This is from 300kHz to 3MHz. Often you will hear about an AM radio station broadcast say something like "ABC Sydney on 702". This means frequency 702kHz.

The next step up is HF. This is a very interesting range. It is from 3MHz to 30MHz. The reason it is so interesting is that a signal can travel around the world with very low power because the signal bounces off the higher layers of the atmosphere and back down to earth. It can do this several times. Many old army radios operate in these bands, and can be easily modified for amateur use. This is how many hams got into radio.

VHF is from 30MHz to 300MHz. There is a band at approximately 50MHz used by amateurs called the "6 metre magic band". It's best in summer due to the way the weather affects the atmosphere, and can travel long distances, but not as far as HF. A lot of hams classify 50MHz as HF, though technically it is VHF. Many multi-band amateur transceivers will share the 50MHz antenna connector with the HF connector. There is also a band at approximately 144MHz. In the US there is a 220MHz allocation that is nicknamed the "action band".

UHF covers 300MHz to 3GHz. There are three amateur radio allocations in UHF, one at approximately 430MHz, one at 1.2GHz and another at 2.4GHz, which shares some frequencies with WiFi standards. This actually permits hams in Australia (and other parts of the world) to transmit much high power for a WiFi network than most regular consumers would be allowed. This is where the real-world practicality ends for ham radio, though specialist groups do operate in higher bands.

SHF covers 3GHz to 30GHz. These frequencies are bordering the limits of what most amateurs are able to play with given that specialized equipment is required to build, maintain and use radios, antennas and cables in this range.

EHF is 30GHz to 300GHz. Very expensive commercial systems used for satellites and military systems work in this range. They are so expensive because of the technology involved and the difficulty in making this stuff work. There is nothing to prevent a ham from building a transmitter in this range except for engineering skill and ability. Because of this, there may be nobody else up here to talk to!