Does the signal simply pass through multiple radio towers?
In: Technology
It is done a few different ways. A radio repeater is used, you could think of it as playing whisper down the lane with a device that listens and repeats what it hears. The other main method is to bounce it off the ionosphere, this is kind of like trying to bounce a ball around a corner by using the wall opposite the corner.
Think of radio towers like big lightbulbs changing their color(FM radio) or brightness(AM radio) to send a message, you can see the light from around corners (curves of the earth) from the bulb lighting up the wall and the wall glowing like the lightbulb (atmospheric reflection). Things like the color of the wall (gasses in the air), how bright the room is (time of day), or things on the wall can mess things up(clouds and such), so you can really only use this for brightness and not color(Because the color can be changed and not all colors bounce off the same things). But this doesn’t make the light brighter so it will only be seeable for as far as you can see the light normally.
Or you can play a game of telephone by having one lightbulb copy another lightbulb’s message. But this can cause the message to be delayed as each light in the chain needs to repeat what they see.
The main way this happens without the signal being repeated by active devices like a satellite or retransmitting stations is via layers of electric charge in the ionosphere. Radio waves can reflect between these layers and the earth multiple times to make the trip. They can also scatter at angles from sharp features (knife edge diffraction), travel between layers of differing temperature in the atmosphere (ducting), reflect off the ion trails of meteors, aurora, or even the moon. There are many more propagation modes I’m not thinking of right now. All of these modes have a different sound. If your interested in learning more, ham radio is a great hobby that exercises all of these techniques. It’s magical to try this out for yourself either by listening or even transmitting (with a license) to see what you can accomplish.
To overcome the curvature there are basically two methods.
The first one uses reflection. At certain frequencies the higher layers of the the atmosphere will reflect the signal and this way you can reach areas that are over the horizon. Ham radio operators are doing it for example.
The second, more modern method is using satellites. You send a signal to a satellite and it will recieve and forward it
If you are asking about single transmitters, some types of radio waves have trouble piercing the atmosphere and “bounce” off. This allows stations over-the-horizon and out of line-of-sight to pick up the signal.
You’re right that there are more complicated network methods to reliably get a signal to distant places. The signal can be picked up and re-broadcast (at the same or different power). The signal can be picked up, uplinked to a satellite, transmitted from satellite-to-satellite and then either re-broadcast by the final satellite or downlinked to a terrestrial station for broadcast. The signal can be picked up, transmitted by undersea cables and re-broadcast. Lots of network solutions are possible.
Radio can bounce off the atmosphere, and that is a thing that gets done, especially for shortwave radio, but largely you got it right, the curvature of the earth is the general limit for how far a radio signal can go on earth. Things mostly do need repeaters on the ground or to go up to a satellite then back down to go farther.
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