Here is something that I can't see has been written about space junk. This is the debris that is left in orbit from rockets and satellites. There are countless small pieces of metal that are in the news as a danger to spacecraft, since they are typically moving at high speed. But there is a potentially positive side to this space junk.
What about radio communications? These countless pieces of metal will reflect radio waves. By reflecting the waves back to earth this could greatly increase the range of the communication. To the space community, space junk is certainly a negative. But to the radio community it could be a positive.
The principle of reflecting radio waves so that they are not limited in range by the curvature of the earth has long made use of the ionosphere. This is a high layer of the atmosphere where the energy of solar radiation knocks electrons out of atoms, thus creating ions that reflect certain wavelengths of radio waves. This enables radio transmissions to extend far beyond the horizon, and are not limited to line-of-sight.
"Skip" is a term that is used when the waves bounce between the earth and ionosphere, greatly increasing their range, possibly to the entire earth. For waves of the longest wavelength, the ionosphere can act as a "wave guide", rather than reflecting the waves.
The ionosphere actually consists of several layers, from a radio perspective, which are affected by the sun. This means that a wavelength which does not get reflected, so that it gets through to the receiver, during the day may get reflected at night, and vice versa.
It was common for a shortwave radio station to broadcast the same transmission on several different wavelengths so that, for any given place and time of day, at least one of the broadcasts was sure to get through. The band that is used for AM (Amplitude Modulation) in North America is typically from about .5 to 1.6 mhz and it is easy to see that more stations can be received at night than during the day. That is because the signals from distant stations are reflecting off the ionosphere.
The ionosphere is limited in it's usefulness because it doesn't reflect waves shorter than about 10 meters and these are the most useful because shorter wavelengths, which mean higher frequencies, can carry more information. Transmissions with a lot of information, such as video and high-fidelity sound, require these short wavelengths.
That is where satellites come in. Satellites receive these broadcasts and retransmit them back to earth, so that they are not limited to line-of-sight as shorter wavelengths usually are.
Talk radio, or voice telephony, doesn't require as much information as music. In the early days of radio the longest waves, which can carry the least information, were useful only for signalling in Morse Code. Random radio noise, such as from lightning, affects the amplitude of waves. This is why AM (Amplitude Modulation) is most vulnerable to noise. This can be avoided by modulating the frequency (FM), rather than the amplitude. But changing the frequency, over a limited range, of course requires the use of a higher-frequency band.
Radio waves move at the speed of light, about 300 million meters per second. Frequency is measured in hertz (hz), which is a wave cycle per second. This means that a wave with a wavelength of one meter will have a frequency of 300 mhz (megahertz).
Now back to space junk. Electromagnetic waves are reflected by objects that are of similar scale to the wavelength. When you drive under a bridge with the radio on the longer waves, such as AM in North America, it fades because they are reflected away by the bridge. But shorter wavelengths, such as FM, are still received because they are reflected around and under the bridge. Still water acts as a mirror because it's molecules are small enough, relative to the wavelength of light, and are held to a flat surface by hydrogen bonding. The sky is blue because the particles of dust that are small enough to remain airborne are the right size to scatter the blue wavelength of light.
If two, or more, pieces of space junk happened to be placed so that a radio wave from earth encountered them at exactly the same instance, then there should be some reflection of the wave. This could be a whole new frontier for long-distance radio. Admittedly the internet has made such broadcasts less important than they once were but this space junk is effectively a new, and higher, layer of the ionosphere that will reflect longer waves back to earth. Amateur radio operators could explore this new layer. Unlike the ionosphere it wouldn't be affected by the sun.
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