On 3/1/2020 7:47 PM, Don Kirk wrote:
Hi Rick, One more comment. I believe AM broadcast stations try to avoid phase cancellation between skywave and ground wave, and therefore they try and avoid antennas that have a high angle lobe. I'm pretty sure that's why the AM broadcast stations that tried such things as a 5/8 wave length radiator determined that this caused phase cancellation problems between ground wave and skywave and abandoned radiators that were this tall. (I might have some of the exact details incorrect, but believe I have listed the general problem they ran into which caused them to rethink ground wave versus skywave and their antenna designs).
Correct. The 5/8-wave radiator (225 electrical degrees) suffers the destructive fringe mixing you described. By backing off to a 190 degree radiator, problem solved. Such antennas have the benefit of strong low angle radiation with no higher angle lobe, and are easier to match at the feed point than a half-wave vertical.
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