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Re: Topband: Skywaves from Monopole Surface Waves

To: <topband@contesting.com>
Subject: Re: Topband: Skywaves from Monopole Surface Waves
From: "Tom W8JI" <w8ji@w8ji.com>
Reply-to: Tom W8JI <w8ji@w8ji.com>
Date: Tue, 9 Oct 2012 10:31:27 -0400
List-post: <topband@contesting.com">mailto:topband@contesting.com>
So again my question - if this low-angle ground-wave (aka surface-wave) energy dies off so quickly (e.g. down 20dB at just 20 miles), how does any of it get to the ionosphere where it can be useful for topband DX?

Is the disagreement about how useful the really low angles are, or is the disagreement about if a low angle measurement (groundwave) is meaningful in determining changes in radiation at useful higher angles?

Groundwave has no value at all for working long distances, and under nearly all conditions extremely low angles have no value on 160 meters for DX.

On the other hand, I don't think many would dispute a groundwave measurement of FS changes between various vertically polarized radiators would be closely tied to FS at usable higher angles. The exception would be those cases where high angle horizontal propagation is a dominant mode.

I have about ten pages of ABC tests from here to VK/ZL and I'm pretty comfortable that angles at or below 20 - 30 degrees dominate almost all of the time, with the most common exceptions only at sunrise or during geomagnetic disturbances. This even compared a dipole at about 280 feet effective height above ground, so there was "lowish" angle horizontal polarization in the test.

Groundwave is a very good way to evaluate vertical antenna efficiency, but certainly not a horizontally polarized mode. I know someone who measured a horizontal antenna at a modest distance and claimed he improved efficiency 10-20 dB by removing his balun and altering feedline length. :-)

We never want to measure in a null or on the slope of a null. That's why we can't measure low horizontally polarized antennas at very much distance, but why verticals are fine.

73 Tom
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