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On Wed, 20 Apr 2005 19:27:22 -0400, "JimH" wrote:
"Dan Krueger" wrote in message link.net... The difference in four feet (assuming the same gain the the antennae) you will only be able to communicate 1.18 miles further. True, or close to it depending on the db gain you used. ;-) Calculation for Range of an Antenna: 6db Antennas: Square Root of Height (in feet) above water x 1.15= Range in miles 9db Antennas: Square Root of Height (in feet) above water x 1.52= Range in miles So we are talking a range of roughly 3 miles for the 4 foot vs 4.25 miles for the 8 foot. Not a big difference as you said. You have to remember that the db figure is based on a free space formula - in short, an imaginary antenna range - it's all math and perfect performance. In the real world it's not any where near 6 db for a variety of reasons including standing waves, ground conditions, radio performance, height, ground plane, data, data, data. The reason manufacturer's can advertise the specs is because, in theory, that's what the antenna will produce given perfect conditions. Also be careful about the line-of-sight deal. FM also relies on ground wave much as AM does - it's the reason you can receive an FM station more than line-of-sight from the FM station antenna. By the way, there is no such thing as a 9 db antenna unless you are talking about a Yagi. Later, Tom |
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