There are many ranges of frequencies (bands) allocated to the amateur radio service from 135 KHz to 250 GHz. Different bands lend themselves better to different activities and amateurs can take advantage of them all.
The 160 meter (1.8 to 2 MHz) band is not for condo dwellers. A half wave length antenna is over 260 feet long! This band is generally noisy in the summer months. It is usually uncrowded and you are likely to find some good ‘ole boys on the air.
The 80 meter (3.5 to 4 MHz) band is good for night time communication. The lower frequency is reflected off the ionosphere even though the sun is down. Higher frequencies tend to pass right through the ionosphere and head out into space without the suns radiation. This band is so large that it is difficult to configure an antenna that will be resonant at both ends.
The 40 (7 to 7.3 MHz) meter band is good for day time communication. It is less crowded than the higher frequencies and occupies a sweet spot between ionospheric reflection (good) and absorption (not good).
The 20 meter (14 to 14.350 MHz) band is probably the most used in the HF range. Only 2 meter VHF is busier. You can find activity on this band whenever conditions permit. A maritime mobile net is held at 14.300 MHz every day from noon til evening.
The 6 meter (50 to 54 MHz) band is considered VHF. When this band opens there is always a lot of activity. When it closes there is virtually none. All VHF and higher frequencies are open to technicians. No general license is required.
The 2 meter (144 to 148 MHz) band is the most popular band by far. It is used for local communication and there are repeaters all over the planet to extend the range of mobile and portable radio equipment. Many repeaters are linked through the internet allowing world wide communication from your car or a handy-talkie.
The 70 centimeter (420 to 450 MHz) band is not as popular as 2 meters but it is generally used the same way. Some amateurs like to make contact on 2 meters and then switch to this band for a rag chew. There are many repeaters supporting this band.
The 33 centimeter (902 to 928 MHz) band is also less supported by amateur equipment manufacturers. You’ll still find activity on this band with commercial radio equipment that has been modified or reprogrammed for amateur use. You may even find a repeater or two in your area.
The 23 centimeter (1.24 to 1.30 GHz) band is not for the faint of heart. But even at this frequency you will find high speed data transfer and EME (earth to moon to earth) communications going on.
The 2.3 to 2.45 GHz bands are generally used for high speed data over very short distances. Amateurs have reprogrammed WiFi routers and other equipment to create ad hoc data networks capable of supporting high speed data such as streaming video, voice over ip (phone) and email systems.
3.3 GHz and Beyond
The 3.3 GHz and higher bands are used at very low power. Groups specializing in this activity call themselves weak signal societies. Surprising distances have been achieved from mountaintop to mountaintop. Radio equipment is more difficult to find. You must usually start with a lower frequency radio and add a transverter to boost the frequency.