Topband: T Top Verticals and yagis

[Augie "Gus" Hansen]

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