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Author Topic: GP height over ground  (Read 574 times)
MM0TWX
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Posts: 2




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« on: January 13, 2014, 07:04:23 AM »

Hello,

Researching on the internet, I found precious few references discussing what effect on radiation patterns has the height at which you mount a GP for the HF bands. The one comprehensive analysis (based on modelling) says that heights between 0.25 and over 1 WL are a big no-no, as most of the energy is radiated at high angles.

Can anybody please confirm, or share additional wisdom.

Thanks and 73.

Pete MM0TWX
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W5WSS
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Posts: 1688




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« Reply #1 on: January 13, 2014, 07:29:18 AM »

Hello Pete, The quarter wave vertical section and a quarter wave grouping of symmetrically placed horizontal radials is radiating from the vertical section exclusively when the radials are properly installed and held symmetrically.

This means the radials being half the antenna can radiate but do not when they are cancelling themselves as is the expected case for the ground plane antenna.

The elevating of the ground plane antenna does involve pattern changes relative to the earth surface so yes the ground plane goes through pattern evolution relative to it's base height above the surface of the ground.

There are graphs that demonstrate the evolution relative to percentage in wave lengths.

The graphs reveal a simple point to be understood.

That with height above ground the pattern evolves into multiple lobes and nulls while maintaining an Omni directionality simultaneously.

Yes you can see that you get more lobes AND nulls with height.

If you want to present a lobe at a target with a ground plane then a specific height can be chosen yes even though it is Omni directional around the circle different power express as field strength are manifest in angles upwards towards the horizon.

A Ground plane at 1/4 wave length of base height is a good DX choice with power trajectory held within about 12 to 16 degrees of angle upwards....when installed higher and the pattern begins to include nulls AND lobes as a subset within the Omni directional overall foot print.

73

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KB4QAA
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Posts: 2334




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« Reply #2 on: January 13, 2014, 08:37:38 AM »

"Pattern Evolution" a wonderful description.  Thanks. b.
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W5WSS
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Posts: 1688




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« Reply #3 on: January 13, 2014, 08:48:06 AM »

 Smiley Glad to invent new terminology designed to be easier to understand for laymen such as myself...lol.

73
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