Neil Carr G0JHC wrote:
>I have had good success with EWE antennas on 160m 12.5 x 5m, but appreciate
>over average ground the take off angle is around 35 degrees when using
>nothing more than a copper 1-2m ground rod. ON4UN (latest book, Chapter 7
>"Receive Antennas") suggests one can lower this angle of reception to be
>more DX orientated by installing a better ground and radials.
>
>Here is my question.
>
>An EWE has 2 grounds, would I only be interested in improving the ground and
>running some radials off the ground rod in the direction of reception, or
>would I benefit from radials to lower the reception angle at both the
>resistor termination side and the 9:1 feed point?
>
>Neil G0JHC
>
>
>
My simulations do not show the ground resistance making any significant
difference to the take-off angle for an EWE. A really poor ground made
the take-off angle of a single element version go up by only 1 or 2
degrees. With a two element version the take off angle actually went
down a small amount with a poor ground. However there are other effects
with a poor ground that are not desirable. The gain decreases, the
front to back ratio decreases, and determining the proper value for the
termination resistor becomes more difficult because it is difficult to
figure out how much of that termination the ground contributes and how
stabile that is going to be. A less obvious effect occurs if the
feedlines are not very well decoupled by transformers having a high
degree of common mode rejection. A poor ground will cause more common
mode currents from the feedlines to be injected into the signal path.
There are benefits to be gained by improving the ground at both ends of
the antenna. If you use radials instead of ground rods, run them
perpendicular to the antenna, not in line with it.
You just reminded me of something I was going to do, improve the
grounding on my 4 element EWE (2 elements used at a time). I don't have
a common mode problem, and the antenna works very well, but I could use
that extra 4 dB gain and 8 dB front to back I am loosing because of a
poor ground. My 4 ft ground rods measured 375 ohms each. Sounds like a
good spring weather project.
Jerry, K4SAV
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