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Monopoles Using Unequal Length Buried Radials

R

rfry

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 graphic from a NEC4.2 study showing how unequal-length buried radials affect the radiated groundwave field 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 monopole driven against 120 buried radials, each 1/4-wave in length.

Changing earth conductivity in that NEC4 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.

R. Fry

Monopole_Unequal_Length_Radials.jpg
 
I know of one directional AM station which, in an attempt to reduce their RF radiation in the direction of their null, severed the ground radials on that side of their array.
It didn't reduce the signal strength in their null. It merely changed the shape of their pattern slightly.
 
WNEX-AM in Macon, Georgia used to do a great job of reaching places like New Zealand, after the city cut half their ground system while building new streets in the neighborhood.
 
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