how does a short wave radio allow you to speak to someone who’s in a whole different country?
In: Technology
tl;dr – shortwave radios use comparatively long wavelengths that are harder to disrupt and can travel farther, use a *lot* more power to help signals travel farther, and use antennas to increase the direction that the power is focused to allow it to travel farther.
Most people’s understanding of how radios work comes from the radios they have in their everyday life – WiFi and cell phones. While they both use similar general fundamentals about how radios work, there are some differences that should be highlighted:
* “Shortwave” is a bit of a misnomer these days because the wavelengths they use for transnational and transcontinental contact are actually really long compared to what cell phones and WiFi uses. Shortwave radios will measure their wavelengths in meters – 144 MHz (a common amateur radio band) is 2 meters in length, while 2.4 GHz has a wavelength of 12.5 centimeters. The shorter the wavelength, the easier it is to disrupt the signal. The shorter the wavelength, the more data you can stuff in there which is why modern systems tend to go to higher and higher wavelengths.
* Lower wavelengths can actually bounce off of certain layers of the upper atmosphere, allowing you to bounce signals to hit distant points that would normally be out of range due to curvature of the earth
* Shortwave radios can use a *lot* more power. WiFi uses 100 milliwatts to cover your home; by comparison, the 3.5 MHz amateur radio band (80 meter wavelength) has a maximum power of 1500 watts, or 15,000 more power that can be used.
* The other main difference is the antenna. Antennas are used to radiate power, can different antennas ran radiate power in different distribution patterns, meaning you can point power more in one direction than another. WiFi is designed to be as general purpose as possible, which means that since the radio builders don’t know how people will use it they want to radiate power as equally as possible in all directions. Advanced antenna designs such as a parabolic dish or a Yagi can allow you to reshape the power so >90% gets focused in a small direction, which allows the signal to travel significantly greater distances.
As you know, the Sun emits a stream of electrically-charged particles, which are responsible for the beautiful [Northern Lights](https://i.imgur.com/8DMPaBz.jpg).
The area of the atmosphere these lights occur in is called the *ionosphere,* so named because it’s filled with ionized air due to the Sun’s particles. Shortwave radio is exactly the right frequency that, when the waves hit the inner surface of the ionosphere, they bounce off and return to Earth. This permits shortwave radio to travel a lot farther than you’d expect, allowing radio operators in America to speak to people on the other side of the world.
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