In radio, propagation just describes how a radio wave travels and behaves. Radio waves are electromagnetic waves and just like light waves are subjected to things such as refraction, reflection, absorption and scattering.
There are many kinds of propagation but the type you might be most familiar with is line of sight propagation. Line of sight propagation means that when the wave is transmitted, it generally doesn’t make it past the horizon and can be blocked by things such as tall buildings or large hills.
This is a popular type of propagation, most cell phones, wifi, walkie talkies and FM radio use line of sight propagation. This type of propagation uses higher frequencies and can be affected by moisture in the atmosphere.
Another type of propagation is ground waves. Ground waves utilize lower frequencies which naturally are able to go farther. These waves can travel beyond the horizon and even around the world when using the very low frequency range and the extremely low frequency range.
AM radio uses ground waves which is why you can generally hear AM radio from a farther distance than you could with FM radio. These low frequencies can even travel through water which makes them ideal for the military trying to communicate with submarines.
The next type of propagation to discuss is called skywave. Up above the earth there is a layer of charged particles called the ionosphere. Because radio waves are electromagnetic, you can actually bounce your radio wave off of the ionosphere and have it be reflected back down to earth. This enables you as a HAM operator to talk to people and places around the world.
Skywave propagation also includes other types of propagation such as meteor scattering, auroral scattering and sporadic E propagation. Opportunities for meteor scattering propagation don’t last very long.
Propagation for HAMs
The cool thing about HAM radio is that we are able to utilize all types of propagation to talk to fellow HAMs. The trick is knowing how to use the different propagations, when to use them, what frequency to shoot for for your specific goal and how to use them.
Line of sight propagation is the easiest and is usually used for higher frequencies, generally above 2 MHz. You can use line of sight for most handheld radios and car radios where you aren’t looking for your signal to travel long distances. You can utilize line of sight propagation any time of the day or year and the taller your antenna, the better.
Ground wave propagation is used for long distance or short distance communication usually at frequencies between 3 and 30 MHz. Ground waves are bouncing back and forth from the ground to the ionosphere and are able to travel a lot farther.
It is best to try your hand at ground waves at night because the reflection characteristics of the ionosphere are better at that time. Using an antenna that is vertically polarized will be your best bet for ground waves because a large portion of the power is radiated at an angle close to the earth’s surface.
The ionosphere is an electrically charged layer of the earth’s atmosphere and is helpful in reflecting radio waves back down to earth’s surface. Skywave also utilizes the frequencies between 3 and 30 MHz and is best used at night when the sun’s radiation hasn’t caused the atmosphere to change in a way that allows the waves to pass right through it.
There are many different kinds of propagation that us HAM radio enthusiasts get to choose from. Propagation in radio just describes how the wave is behaving. We talked about three really popular types of propagation used by amateur radio enthusiasts.
Line of sight propagation only travels as far as the horizon and is easily blocked by tall buildings and hills and works with UHF/VHF ranges. Ground waves can travel farther because of the way they bounce back and forth from the ground to the ionosphere. Skywave works the best at night but is the easiest way to reach distances all the way around the world.