Stacking dipoles like in the FM radio world produces significant gain of
course. If the dipoles are of the same polarity and properly stacked and
fed you can double your radiated power every time you double the number
of radiating elements. I would like to add that one of the simplest ways
to get gain from a wire antenna is with the the legendary Bobtail which
consists of three vertical 1/4 wave wires hung from a full wave
horizontal wire. (a single vertical drop on each end of the flat top
and a 1/4 wave feed wire from the exact center) This fixed wire non
rotatable antenna produces a broadside pattern , great for DX, and
doesn't break the bank in the process. On 40 meters only two wooden 40
foot poles space 130 feet apart are all that are required required as
metal towers tend to ruin the pattern. So either your friend at the
telephone company or off to the lumber yard after renting a post hole
digger is about all that is required.
Herb Schoenbohm, KV4FZ
On 12/10/2014 1:12 AM, Jim Brown wrote:
On Tue,12/9/2014 1:46 PM, Ken wrote:
In actuality, “gain” in a non rotatable antenna is a myth.
False. Gain for antennas is usually expressed as dBi, meaning dB
referenced to an ideal isotropic radiator. Gain is not a single number
(unless the antenna is isotropic) -- it varies with both vertical and
horizontal angle.
An ideal (lossless) dipole in free space has a PEAK gain (that is,
broadside to it) of 2.18 dBi. Mount that dipole horizontally over real
ground and the earth provides a reflection in the far field that
creates a vertical pattern. Assuming no earth losses, the Peak gain
will now be 3-6 dB greater at the vertical angle where the direct wave
from the antenna combines precisely in phase with the wave reflected
by the earth.
The shape of the vertical pattern will be entirely dependent upon the
height of the horizontal dipole as a fraction of a wavelength, but
will be almost independent of soil conditions.
Mount that same dipole VERTICALLY and it will interact very
differently with the earth, and will be VERY dependent on the quality
of the soil. There are some tutorials about all of this on my
website. k9yc.com/publish.htm
http://k9yc.com/VerticalHeight.pdf
http://k9yc.com/VertOrHorizontal-Slides.pdf
73, Jim K9YC
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