On Sat, Sep 24, 2011 at 3:30 PM, Guy Olinger K2AV <olinger@bellsouth.net> wrote:
> EZNEC's "fresh water" selection shows a conductivity of .001 (very
> unconductive). So it's talking about Great Lakes fresh water away from urban
> polution.
Leaving the conductivity at 1mS/m and changing only the permittivity
from 10 to 80 in a NEC-2 model of a 160m quarterwave over 20 78 foot
radials gives a big boost to the low angle radiation. About 4dB
improvement at 13 degrees and 7dB at 2 degrees.
>Anybody care to go out in the middle of your local freshwater swamp and
>stick ohmmeter probes down there? The conductivity may even be layered,
>since the water with dissolved materials will weigh more and the more fresh
>will lay on top.
The USGS water data site might be an interesting resource. The stream
near my house always averages between 30 and 60 mS/m (300 and 600
microsiemens per centimeter) for the past six years:
http://goo.gl/7mE5m
"Urban pollution" is certainly a potential issue here... but we can
look around many sites. 30mS/m recently up in the Potomac up in West
Virginia. Here's Lake Champlain @ Burlington VT (probably at an
inlet?)
http://goo.gl/TGSCK
The conductance meters happen to be installed on the couple stations I
care about for other reasons, but maybe not around the rest of the
country. If you click a state and then choose "build sequence,"
simply hit "SUBMIT" under "Site Selection Criteria" and check
"specific conductance" and hit "submit" again you can find all the
stations that have a conductance meter.
I have yet to see anything as low as 1mS/m (10 microsiemens per cm) in
spot checks. Found some in Georgia that went down to 5mS/m when it
rained a lot.
Anyway, just some thoughts.
73
Dan
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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