Topband: Anyone purchased the ARRL book on Short Antennas for160???

[Richard Fry]

Dave W0FLS wrote:
> With the radials being 4.9 meters above ground, do the radials literally 
> come up to the tower and then travel down the leg to connect to the ground 
> side of the insulator or do they travel in close to the tower and angle 
> downward?

>From the text of that paper, it appears that the four horizontal radials are 
attached to the monopole by insulated supports at 4.9-m elevation points 
above the earth, and terminate there.  The coax center conductor is bonded 
to the tower at that same elevation, and the coax outer conductor attaches 
to the common point of the four horizontal radials at that elevation.

There is no need as far as system radiation efficiency for any of the 
conductors of this antenna system to have a physical connection to the 
earth.  Probably this system does have conductive paths provided by a static 
drain choke to a "lightning ground" buried in the earth (maybe a few ground 
rods), and an arc gap across the base insulator -- but the paper did not 
include those details.  They would have almost no affect on the radiation 
efficiency of this system, in any case.

> Does a FS measurement taken at 1 kilometer fully reflect the true angle of 
> radiation and overall performance of the antenna for purposes of distant 
> signals?

The relative field (E/Emax) of the vertical plane field pattern radiated by 
__all__ monopoles of ~ 1/4-wave in height and less is very close to the 
cosine of the elevation angle.  The cosine of zero degrees is 1 (unity), 
which means that maximum field is radiated toward the horizon.  The cosine 
of 30 degrees is 0.87, which means that the field at that elevation angle is 
87% of the field in the horizontal plane.  Etc.

Referencing back to Clarence Beverage's data, this means that the field at 1 
km radiated by that system toward a 30-deg elevation angle is 0.87 x 302 
mV/m = 263 mV/m (approx).

The relative values of those fields at an infinite distance over a 
real-earth ground plane no longer have the relationships they had at 1 km, 
but that does not alter the fact that those relationships existed at that 1 
km distance, in the first place.

R. Fry