It is precisely the high measured levels with merely 2 radials that
gives me pause.
After publishing the FCP I get new stories almost on a daily basis.
It's very common for two elevated radials to perform abysmally, with
"startling improvements" upon upgrading to a proper field, or changing
to an FCP. I have no success stories about two radials that would
come close to the performance of the two radials in figures 30 and 32
in BL&E.
At the current time, the only way I can explain what happens in BL&E
with the two radials is really rather good dirt. Though I know (after
having been corrected by you) that they were saying 2 mS/m on the
graphs, *I* live in sandy or clay soil with some acid content from
decaying tree leaves and loblolly needles. I might be 3, or 4 at best.
I can tell you for a fact that two radials HERE does NOT perform like
that graph, nowhere close.
The other problem I have frankly is that they produce graphs for both
2 and 10 mS/m. Which was it they were measuring? Or are we looking
at extrapolations on something. Why isn't the actual conductivity
simply STATED and graphed at that conductivity? And then you have the
corollary question, when they made the extrapolations to 2 and 10 from
whatever it really was, what assumptions and math were they using, and
how did they calculate it? That kind of extrapolation would have been
a real bear with 1937 tools.
If that measurement at 3 MHz for two radials was over 4 mS/m, and it
was dead on, and the extrapolations to 2 and 10 mS/m were accurate,
then there is a mode shift or something by the time we get to 1.825,
because two on-ground 1/4 w radials on 160 over what the FCC estimates
is 2 mS/m North Carolina dirt just plain sucks. And merely down 3 dB
or even 6 dB from an overkill radial field like the high count jobs in
BL&E does NOT explain it, or come remotely close.
Something, somewhere, in all of this, does not add up. That graph says
that with two buried radials you only take a 3 dB hit in that dirt at
3 MHz. A new meaning to "not in my backyard".
I do hope you can find some more specific information.
How many old RCA guys do we have on this reflector?
73, Guy.
On Thu, 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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