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Post by Boomer on Nov 5, 2017 10:32:33 GMT
Quick reply, good stuff davec, the calculation with 3.2% radiation efficiency, that's a good deal more that ever seen with a base loaded monopole with no top hat. In this game, I've never seen numbers that good, they're usually well below 1 percent efficiency.
Electron Bunker's site is great, the home of the tube AM stereo transmitter, an article I've read over and over in study, as I'm an AM stereo believer.
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Deleted
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Post by Deleted on Nov 5, 2017 16:03:34 GMT
Yes, the top hat can be considerably more efficient than a single wire monopole. But, both types of 3 meter ground mounted antennas are constrained by physics to relatively low efficiency. 0.3% for a CB whip, 1% for a very fat wire, and 5% for a top hat monopole at the high end of the AM BC band.
The popular way to obtain relatively high radiation efficiency is to elevate the "antenna" on a mast or building. As we all know, the mast, or ground lead, becomes part of the radiating antenna. As a first-order approximation the radiation efficiency is proportional to the square of the antenna current-area. The current-area of a 3 meter base-loaded monopole is 1.5 A-m (Ampere-meters) and its current distribution is trianular. The current area of a mast, or ground lead, is equal to its length because the current is uniform along its length; its current distribution is square. A 3 meter mast below the "antenna" has a current-area of 3 A-m and placing the 1.5 A-m antenna on top gives a total current-area of 4.5 A-m. The radiation efficiency is increased by the square of (4.5/1.5) = 9. The formerly 0.3% efficient antenna is now 2.7% efficient. A formerly 0.1% efficient antenna is now 0.9% efficient. Place the 0.1% antenna on a 6 meter mast and its efficiency increases to 2.5%. This continues until the radiation resistance begins to approach the system loss resistance at which point the efficiency improvement begins to level off.
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