According to ARRL (National Association of Amateur Radio), 73 is known as a “friendly word between operators”. Because Ham Radio (also known as Amateur Radio) is wireless, the operators are more than just enthusiasts. At local levels (10+3), they offer vital assistance during disasters. “For instance, it was the Amateur Radio Service which kept New York City agencies in touch with each other after their command center was destroyed during the 9/11 attack. Ham Radio came to the rescue during Hurricane Katrina, where all other communications failed.”
In addition, the operators are important at a global level (10+7). “Hams are also ambassadors for their country. Radio provides the opportunity for communications with hams in nearly every other foreign country.” There are estimates of 600,000 to 650,000 amateurs (10+5) in the United States and 2,000,000 to 3,000,000 (10+6) around the world. It’s harder to get an accurate count since you don’t have to be a ham operator to participate. You can have a ‘receiver’ and just listen.
With a ham radio, you can learn to talk with someone on your neighborhood (10+3), in your state (10+5), across the country (10+6), on the other side of the world (10+7) and maybe even in space (10+8).
How does Ham Radio work? “During daylight, 15 to 27 MHz is a good band for long-distance communications. At night, the band from 1.6 to 15 MHz is good for long-distance communications. These bands are often referred to historically as short-wave bands (as in “short-wave radio”). Unlike frequencies used by FM radio stations and TV stations, which are line-of-sight and therefore limited to 40 or 50 miles, short-waves “bounce” off the ionosphere from the transmitter to the receiver’s antenna. The higher the frequency is, the “shorter” the wavelength is.”
Here is a helpful diagram from a NASA educational website of how high frequency waves travel through the ionosphere. “The ionized part of the Earth’s atmosphere is known as the ionosphere. Ultraviolet light from the sun collides with atoms in this region knocking electrons loose. This creates ions, or atoms with missing electrons. This is what gives the Ionosphere its name.” Free electrons (10-18) in the ionosphere are how the radio waves can travel so near and far because they can absorb or reflect the radio waves.