Topband: Affect of Unequal-length Buried Radials on Monopole Radiation Patterns

[Richard Fry]

>Here is a clip of a post I made on another website in answer to a question 
>there, which might be of interest here also...

Below is a link to a graphic from a NEC4.2 study showing how unequal-length 
buried radials affect the groundwave fields of a 1/4-wave monopole, for 
approximately the conditions given in the opening post.

The h-plane fields are uniform +/- 0.014 dB.

The ~304 mV/m groundwave fields calculated by NEC over these real earth 
paths are rather close to the ~306 mV/m inverse distance field 
("efficiency") that the FCC predicts for this power and distance for a 
1/4-wave, base-fed monopole driven against 120 buried radials, each 1/4-wave 
in length.

Changing earth conductivity in that NEC model to 1 mS/m d.c. 5 (other 
parameters the same) changes the groundwave field to about 259 mV/m at 1 km, 
with a circularity of about +/- 0.12 dB.

http://s20.postimg.org/vn85ii9kd/Monopole_Unequal_Length_Radials.jpg

R. Fry