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.
Gus Hansen
KB0YH
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|