[TowerTalk] Dipole gain?

[Herbert Schoenbohm]

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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