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@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.
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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