[BC] Class "D" AM Towers

[PeterH]

On Feb 16, 2010, at 6:48 AM, RichardBJohnson at comcast.net wrote:

> For many years the 5/8 lambda tower was called the "anti-fade"  
> tower. When did they change the physics?

Might have been pre-1935, but a true anti-fade radiator is more like  
5/9-wave, not 5/8-wave.

And, we now know, through NEC modeling, that a true anti-fade  
radiator ... the tallest non-sectional with which the high angle lobe  
has not yet become fully formed ... is 195 degrees, not 200 degrees,  
nor 225 degrees.

It is no accident that the average height over all ND-U Class As in  
these United States is 195 degrees, and this height is more-or-less  
the standard for CBS and several independents. There are a few  
taller, such as 880, and s few shorter, such as 640.

And, sectionals, which should be, or were intended to be anti-fade,  
are not necessarily so.

Physics didn:t change, but the interpretation of the results, based  
upon improved modeling and field measurements surely have changed.