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Re: [TowerTalk] THANKS....Phased Verticals 40m......

Subject: Re: [TowerTalk] THANKS....Phased Verticals 40m......
From: Jim Brown <>
Date: Mon, 01 Oct 2012 08:50:15 -0700
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On 9/30/2012 7:29 AM, John Frazier wrote:
Thank you, to all who took the time to offer good insight and experience.

Another important point, John. The DX performance of any antenna is strongly dependent on how it interacts with the earth, and the quality of the earth in the miles around the antenna. The vertical pattern of a VERTICAL, especially the low angle performance, is the result of the first reflection from the earth adding in phase to the direct radiation. The strength of that first ground reflection depends on soil conductivity -- the difference between very good soil and poor soil can be as much as 6dB, and sea water adds another 6dB.

When we add radials to a vertical, we reduce the earth losses in the NEAR FIELD -- that is, within a quarter wave or so, which launches a stronger signal (2-3 dB for a serious ground system), which makes the TOTAL signal stronger, but it doesn't help the SHAPE of the vertical pattern.

Horizontal antennas are very different -- height determines the SHAPE of the vertical pattern, but soil conductivity doesn't change the STRENGTH of the far field signal. SO -- those who say their vertical arrays are outperforming high dipoles probably live in areas where the soil conductivity is very good and have put very good radial systems under them, and those whose high dipoles work better have less wonderful soil.

When we talk about "high" dipoles, we're generally talking about more than a quarter wave above ground. Raising a dipole from one-eighth wavelength to a quarter wave is good for only 1dB at 10 degrees elevation, but getting it up to a half wave is good for ANOTHER 5dB.

In addition, there's the issue of terrain. Horizontally polarized waves interact with the terrain in ways that are rather predictable, and some ground slopes are much "nicer" than others. N6BV's HFTA (High Frequency Terrain Analysis) program, which comes free with the ARRL Antenna Book, is quite good at studying this effect. Those of us who live in places where the land isn't flat have found it quite useful (and accurate) in planning antenna heights. .

73, Jim K9YC

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