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Old 01-13-2010, 11:44 PM
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n5ims n5ims is offline
Join Date: Jul 2004
Posts: 3,622

Power is only a small factor in the distance that can be covered. On VHF and above (generally) Height and how clear the path is much more important than power, at least once you get pased a 'minimum power level'. Antenna design is also a key factor in most situations (please note that this is 'antenna design' and not just 'antenna gain').

I used to regularly talk over 60 miles using my 4 watt power out HT using the rubber duck antenna. This was when I was on the roof of a the tallest building for 20+ miles (just under 300') to a repeater at the 1100' level which was 60+ miles away. Hams on the International Space Station use an HT attached to a rubber duck antenna stuck in a window for their "hams in space" program and this is easy to hear when they're overhead as well.

Another example on how transmitter power isn't the key factor is on the AM broadcast band (often called MW for Medium Wave). Radio stations are often required to reduce power or change antenna patterns at local sunset to reduce interference with other stations on the same or on close frequencies. Some run 5000 watts of power during the day and have trouble covering their local area fully, but are reduced to running 100 watts (or even less) to keep them from interfering with a station 1000 miles away at night.
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