From: kevin.strom@revilo-oliver.com   
      
   Testing the flat Earth idea with broadcast FM radio signals (roughly 100   
   MHz):   
      
   If the transmitting antenna is on a mountain near Los Angeles, for   
   example, at 300 meters high, and the receiving antenna is on a Pacific   
   island on a hill at say, 300 feet, with only ocean in between, there   
   would be no mountains or other obstacles to alter our calculations.   
      
   Let us say that the FM broadcast transmitter is running 50,000 Watts   
   (+77 dBm) into a unity-gain antenna, the receive antenna is also unity   
   gain, and the goal is a 20 dB signal-to-noise ratio, good enough for   
   decent high-fidelity reception. This would typically take a signal   
   strength of -73 dBm at the receiver antenna terminals. Therefore, the   
   allowable path loss is 150 dB.   
      
   The question then is, how far away could the island be from Los Angeles?   
      
   On a flat Earth, you would only be limited by path loss; the horizon   
   could never block anything at surface level or above. So path loss   
   strictly follows the inverse square law rule (loss increases 6 dB every   
   time you double the distance). Running the numbers, the island could be   
   4,700 miles away and still give you perfect reception.   
      
   On a spherical Earth, the radio horizon must be taken into account. For   
   the antenna heights given, the radio horizon is at 60 miles. The signal   
   would still be more than adequately strong at 60 miles, but would   
   attenuate very precipitately beyond that distance. So, on the real   
   Earth, the island could be no more than 60 miles away.   
      
   There actually is a Pacific island in just the right place to use Los   
   Angeles FM stations to test whether or not the Earth is flat. It's   
   called Oahu. It's 2,560 miles from LA.   
      
   If Los Angeles FM stations are booming in all the time there, the Earth   
   is flat.   
      
   If they are not, then the Earth is not flat.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)