Amateur radio is hobby or pastime enjoyed by many. But with readily available cell phone and internet communications it is now usually practiced by an enthusiast rather than for practical reasons. Amateur radio is often used in remote areas where there is little communications infrastructure or when infrastructure is damaged due to a disaster. Amateur radio includes communicating locally or world-wide by two-way radio. It can include striving for "DX" receptions that are challenging, usually because of weak signals due to the distance. Communicating with very low power transmitters (referred to as QRP) is also popular.
Obtaining a license to operate an amateur radio station requires passing an examination covering technical topics and operating procedures. The exact nature of the assessment varies in each country and by the class of amateur radio license the applicant is seeking. In many countries there are different classes of amateur radio license with different privileges.
ITU frequency bands used in telecommunications:[1]
Extremely Low Frequency (ELF) 0.03 Hz – 300 Hz
Ultra Low Frequency (ULF) 300 Hz – 3 KHz
Very Low Frequency (VLF) 3 KHz – 30 KHz
Low Frequency (LF) 30 KHz – 300 KHz
Medium Frequency (MF) 300 KHz – 3 MHz
High Frequency (HF) 3 MHz – 30 MHz
Very High Frequency (VHF) 30 MHz – 300 MHz
Ultra High Frequency (UHF) 300 MHz – 3 GHz
Super High Frequency (SHF) 3 GHz – 30 GHz
Extremely High Frequency (EHF) 30 GHz – 300 GHz
Here are standard antenna lengths for 1/2 wavelength long dipole antennas and 1/4 wavelength long vertical antennas for some of the popular amateur bands:
There are two basic types of antennas, antennas that propagate equal in one direction, i.e. "unidirectional propagation" or antennas that propagate in all directions, i.e. "omnidirectional propagation"