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From: Feedback
Date: 07 Jul 1999
Time: 10:25:24
Remote Name: 208.21.129.248
The CFA and a Very Flat Radiation Pattern: * How far can the conic sections be extended ? The broadcast CFA's featured on your pages have a funnel shaped addition at the top which you say flattens the vertical radiation pattern, increasing the effective radiated power in the ground wave. This appears to channel the radiation horizontally, in about the same proportion as the ratio of width to height. An increase of about 3 to 1 in e.r.p. is quoted. Why not go higher? Many Medium & Long Wave broadcasters do not need any upward radiation at all, so the further this idea could be extended the better. How far can it go? Would a much larger, much broader conic section work? Would the principle fall down if, for example, a 20 to 1 increase in e.r.p. were attempted? This would imply a horizontal beam width of just a few degrees, and a conic section perhaps 20 times wider than the height of the CFA, presumably with a corresponding increase in the size of the ground plane. It would be very attractive to AM broadcasters because it would bring them into line with TV broadcasters who also have no need to radiate upwards, and commonly achieve a 20 to 1 ratio of e.r.p. to transmitter power. Even with a different shape and a larger ground plane it should still be smaller and cheaper than a conventional antenna. The increase in overall size might not have to be as much as 20 times, because of the increase in E plate capacitance due to the difference in shape. Also, from comparing the scale of your 80 metre antenna with the Medium Wave broadcast CFA's, it seems that the existing broadcast CFA's are not at the limit of being as small as is practical, so a smaller model might be used as the starting point for a high gain design. But is such a high gain design possible at all?