Understanding ham radio (or any radio) is impossible without also having a general understanding of the purpose of radio — to send and receive information by using radio waves. Radio waves are just another form of light and travel at the same speed: 186,000 miles per second. Radio waves can get to the moon and back in 21⁄2 seconds or circle the Earth in 1⁄7 of a second. An electric field and a magnetic field carry the energy of a radio wave. These fields affect charged particles, such as the electrons in a wire, and make them move. Electrons move in specific ways: They move parallel to electric fields and in circular motions in response to magnetic fields. These moving electrons (that is, current) also create moving electric and magnetic fields (in other words, radio waves) and vice versa.
Transmitters cause electrons to move so that they, in turn, create the moving fields of radio waves. Antennas are just structures for electrons to move in to create radio waves. The electrons in an antenna also move in response to radio waves launched by other antennas. Receivers then detect the electron motion caused by the incoming radio waves. The energy is just transferred from electrons to radio waves and back to electrons at the other station.
Frequency and wavelength
The radio wave-electron relationship has a wrinkle. The fields of the radio wave aren’t just one strength all the time — they vary between a positive and a negative value, or oscillate, like a vibrating string moves above and below its stationary position. The time a field’s strength takes to go through one complete set of values is called a cycle.
The number of cycles in one secondis the frequency of the wave, measured in hertz (abbreviated Hz).One other wrinkle — the wave is also moving at the speed of light, which isconstant. If you could watch the wave oscillate as it moved, you would see that the wave always moves the same distance (one wavelength) in one cycle. The higher the wave’s frequency, the quicker a cycle completes, and the less time it has to move during one cycle. High frequency waves have short wavelengths and low frequency waves have long wavelengths.
If you know a radio wave’s frequency, you can figure out the wavelength because the speed of light is always the same. Here’s how:
Wavelength = Speed of light / Frequency of the wave
Wavelength in meters = 300,000,000 / Frequency in hertz
Similarly, if you know how far the wave moves in one cycle (the wavelength), you also know how fast it oscillates because the speed of light is fixed.
Frequency in hertz = 300,000,000 / Wavelength in meters Frequency is abbreviated as f, the speed of light as c, and wavelength as the Greek letter lambda, λ, leading to the following simple equations:
f = c / λ and λ = c / f
Radio waves oscillate at frequencies between a few hundred kilohertz, or kHz (kilo is the metric abbreviation meaning 1,000), up to 1,000 gigahertz, or GHz (giga is the metric abbreviation meaning 1 billion). They have corresponding wavelengths from hundreds of meters at the low frequencies to a fraction of a millimeter (mm) at the high frequencies.
The most convenient two units to use in thinking of radio wave frequency (RF) and wavelength are megahertz (MHz; mega means 1 million) and meters (m). The equation describing the relationship is much simpler when you use MHz and m:
f = 300 / λ in m and λ = 300 / f in MHz
If you are not comfortable with memorizing equations, an easy way to convert frequency and wavelength is to memorize just one combination: for example, 300 MHz and 1 meter or 10 meters and 30 MHz. Then use factors of ten to move in either direction, making frequency larger and wavelength smaller as you go.
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