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Old 09-11-2010, 03:14 PM   #13
sptrout sptrout is offline
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Sep 2007
Spring, TX
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"Generally speaking, the sound pressure level in free field such as an anechoic chamber drops by 6dB everytime you double the distance from the souce."

Just a brief change of subject, but kind of along the same line. The 6dB rule applies not only to audio, but the entire RF spectrum well up into the microwave region and above. This is one of the reasons that it really does not matter all that much how far the distance is between the transmitter and the receiver assuming all the losses are "free space" losses (no ground obstructions). The drop is 6dB every time you double the distance. So a 100 mile path has only 6dB more loss than a 50 mile path. 20,000 miles has only 6dB more loss than a 10,000 mile path, and so on. If you can avoid ground obstructions (a high antenna for one) you can communicate a long, long way. Avoiding ground obstructions is not all that feasible on earth (except mountain top to mountain top), but point the antenna towards the sky and the "sky is the limit" (within reason).
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