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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