Re: Avoiding attenuation in radio waves with vaccuum tube?

Hi Pam,

You are thinking in the right direction. It's not just a thought
experiment. What you describe is known as a waveguide:

http://en.wikipedia.org/wiki/Waveguide_%28electromagnetism%29

Transmission lines and some types of optical fibers also fall into the same
category. As you suspected, waveguides are used to transport
electromagnetic power over long distances with low loss.

Here is some detailed information on transmission lines:

http://en.wikipedia.org/wiki/Transmission_line

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