MadSci Network: Engineering

Re: What can i use to bounce radio signals? And how long could i expect them to

Date: Mon May 2 15:18:06 2011
Posted By: Todd Jamison, Chief Scientist
Area of science: Engineering
ID: 1297630489.Eg

Well this is a very open question. When you say "radio signals" it could mean a lot of different things. Radio signals are electromagnetic (EM) waves. Radio frequencies cover the EM spectrum from a few hundred kilohertz up to the gigahertz range. Above that, you get into signals that behave more like light than radio, but they are still very much the same EM waves. Do you have a specific type of radio signal you would like to bounce? EM waves will either be bounced from a material, pass through the material, or be absorbed by the material. Think of a mirror, a window, and a black wall as examples of these three things applied to light (something we can all relate to).

Generally, radio signals "bounce" off of conducting objects, such as metal. That's why antenna dishes are made of metal, because the bounce the signals back to the receiver located in the locus or center.

Now, your question about bouncing forever: What you say is generally true. However, you must consider that EM waves spread out the farther they go, unless they are well "collimated". (Collimated means that the waves are all traveling in exactly the same direction.) Consider a flashlight. The spot on the wall it creates gets bigger, the farther you are from the wall. That is because the light is spreading out - it is not collimated. Also, the light in the spot gets less bright because the same amount of light has to fill a larger area. Radio waves behave similarly. Now consider a laser pointer. Lasers are well collimated light. You can point a laser and it will create a spot at a very long distance. There are radios that generate collimated waves, but they are uncommon. One type is called a MASER for Microwave Amplification through Stimulated Emission of Radiation. MASERs were invented before LASERs and were used in microwave radio transmission.

Even if you could build a collimated radio source, you would still need to consider that the radio wave has to go through the atmosphere and it will interact with the atmosphere and lose some of its energy. Thus, the radio wave will be weakened. If you were in space, the radio wave would travel forever, but it would likely start to spread out and eventually be so weak that it would not be detectable.

RADAR (RAdio Detection And Ranging) uses the bouncing of radio waves to detect things, like airplanes, ships and raindrops. If you want to bounce radio waves off of things, you might do some research on radar and try to build one yourself. It is not an easy task, though. A simple radar just needs an oscillator, a transmitting antenna, a receiving antenna, and some simple circuitry. I'm sure you can find some instructions on the web.
Good luck,

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