[TowerTalk] Vertical with 1 radial

Jim Brown jim at audiosystemsgroup.com
Thu May 12 20:06:25 PDT 2011


On 5/12/2011 1:06 PM, David Gilbert wrote:
> For all practical purposes, a vertical with only one radial doesn't have
> "gain" in one direction ... it merely has more loss in all other
> directions.

YES.  It's important to understand the difference between GAIN and 
DIRECTIVITY.  A Beverage may have 10dB or more of directivity, but gain 
of -20dB.

Last summer, I labored mightily to build two sloping verticals for 160M 
using my 120 ft tower as both a support and a passive reflector. One is 
aimed west, the other east. Both are insulated from the tower and fed 
from their base.  I added four elevated radials to each antenna and to 
the tower (later increasing to about 8 per antenna plus the tower), and 
carefully began making MANY observations comparing the new antennas to 
my existing top-loaded Tee vertical.  NEC predicted, and I could very 
clearly observe, F/B of at least 6dB by switching between the two 
verticals, and the slopers were consistently 6dB quieter on receive.  
BUT -- VERY seldom did the slopers produce MORE signal than the Tee 
vertical with 70 radials, and usually they were a few dB down.  I have 
DIRECTIVITY, but the GAIN is probably less than 0dB in the favored 
direction!

Now, antennas have both horizontal and vertical directivity, and there 
have been rare occasions where the slopers have worked someone that the 
Tee would not.

73, Jim K9YC


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