Topband: Short radials?

[W2XJ]

Richard

The data is indisputable but I think for the average ham about a dozen 45 degree radials will produce about 3 DB less than theoretical. That is less than an S unit. The other difference is that all this information is based on ground wave propagation. There is nothing that addresses higher angle sky wave propagation common for 160 M operation. 

Sent from my iPad

On Sep 27, 2012, at 7:38 PM, "Richard Fry" <rfry at adams.net> wrote:

> Guy Olinger wrote:
> 
>> Can you pass along your source of information that BL&E was done over 4 mS/m soil, ... Or are you using the FCC map for typical soil conductivities and presuming a common New Jersey value and no variation at the site?
> 
> It is my presumption that for their cost and logistics, and with my 15 years of insight as an RCA Broadcast field engineer (1965-1980), the BL&E measurements were made near Princeton, NJ.  I'll try to confirm that, and advise. Princeton was the corporate facility containing the office/laboratory of George H. Brown.
> 
> If those tests had been made at some physical location where earth conductivity at/near the test site was significantly better than in New Jersey, this would have been evident in their measured data.
> 
> For an example of this, if earth conductivity at/near the test site was 30 mS/m, then even relatively few/relatively short buried radials in contact with that earth would enable higher radiated fields than shown in the BL&E data for those radial numbers and lengths. This is illustrated by the NEC4 study using a short monopole on 1.85 MHz at this link: http://i62.photobucket.com/albums/h85/rfry-100/10m_Vert32Buried_Radials.jpg .
> 
> Even for an earth conductivity of 4 mS/m, the BL&E data show that monopoles ranging from about 45 to at least 90 degrees in physical height, driven against an r-f ground system consisting of at least 113 x 0.412-wave buried radials, produces a groundwave field at 3/10 of a mile that is within several percent of the maximum theoretical value possible for a perfect monopole driven against a perfect ground plane, for that applied power.
> 
> The bottom line in all of this is that the worse the earth conductivity within 1/2-wavelength of the base of a monopole (especially a short monopole) while driving that monopole against a set of buried radials, the more important it becomes to use a large number of such radials of lengths approaching 1/2 of a free space wavelength. 
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