[TowerTalk] Impact of high water table levels on antennas

[Jim Lux]

On 11/3/13 6:47 PM, Michael Tope wrote:
> I think that would be true for a fresh water lake, John. OTOH, I would
> expect the the conductivity of water saturated soil to depend heavily on
> what materials dissolve into the water from the dry soil.
>

Actually, it's the size of the soil particles that seems to be the 
biggest effect, RF-wise.  Fine Clay is very different than coarse sand, 
for instance.  Partly it's also that clay can hold a lot more water 
without being "waterlogged", because the particles are smaller.

A soil that is 10% water is quite wet.. Get up to 20% water and it's 
positively soggy.

So, if you think about using a simple mixing rule.. at 20% water, the 
other 80% is "rock" and "air", both of which are fairly non-conductive, 
and low epsilon.  Most Rock is in the 4-5 range for epsilon..  Most dry 
soil has an epsilon around 2-3 (half air, half "stuff")..


There's also huge frequency dependencies when it comes to wet/damp soil, 
and the finer the particles, the bigger the variation

If anyone is interested, there's two papers that are sort of the "go-to" 
reference

M. C. Dobson, F. T. Ulaby, M. T. Hallikainen, H. A. El-Rayes, “Microwave 
Dielectric Behavior of Wet Soil – Part II: Dielectric Mixing Models”, 
IEEE Transactions on Geoscience and Remote Sensing, Vol. GE-23, No. 1, 
January 1985

M. T. Hallikainen, F. T. Ulaby, M. C. Dobson, M. A. El-Rayes, L-K Wu, 
“Microwave Dielectric Behavior of Wet Soil – Part 1: Empirical Models 
and Experimental Observations”, IEEE Transactions on Geoscience and 
Remote Sensing, Vol. GE-23, No. 1, January 1985

as well as

W. A. Wensink, “Dielectric Properties of Wet Soils in the Frequency 
Range 1-3000 MHz”, Geophysical Prospecting, Vol. 41, Issue 6, 27 April 2006

> 73, Mike W4EF...........
>
> On 11/3/2013 3:37 PM, john at kk9a.com wrote:
>> I do not think fresh water has much effect on verticals and even less on
>> horizontal antennas.
>>
>> John KK9A
>>
>> To:"towertalk at contesting.com" <towertalk at contesting.com>
>> Subject:[TowerTalk] Impact of high water table levels on antennas
>> From:Rudy Bakalov <r_bakalov at yahoo.com>
>>
>> Ever since I have put up two inv-Vs, one for 80m and one for 160m, with
>> their
>> apexes at roughly 90', I have been puzzled by their exceptional
>> performance.
>> Ditto for my vertical on 40m.  I have done tons of comparisons using
>> skimmer
>> data and my signal seems to be pretty darn close to the big stations I am
>> using
>> as my benchmark. The performance is so good that I have been wondering
>> if I
>> should bother with building 4SQs. I have read tons of books on
>> antennas and
>> the
>> performance of these two antennas simply does not match what the books
>> describe.
>>
>> I shared my thoughts with a friend of mine (a WRTC2014 participant)
>> and he
>> shared a similar experience with his station. He recently relocated to
>> a new
>> place, about 30 miles from his old place, and his antennas at the new
>> place
>> perform significantly better than the old location. Same antennas, tower,
>> feed
>> line, and FLAT terrain.  His only explanation is that the new place had a
>> very
>> high water table that somehow impacted antenna performance.
>>
>> This is when I realized that I also have a very high water table. Even in
>> the
>> driest months of summer, the area around my tower is damp and the
>> grass is
>> very
>> green, growing like crazy. This was the obvious common element between
>> his
>> and
>> my situations.
>>
>> I have not seen anything on high water tables in my antenna books.
>> The soil
>> itself is mostly sandy. The impact I believe I am seeing is mostly on the
>> lower
>> bands, but I am not sure if this is also the case on the upper bands
>> as at
>> 105'
>> my antennas are a bit too high.
>>
>> Is there any rationale in our thinking? Can high water table explain
>> better
>> than expected performance from low band antennas? If so, what is the
>> theory
>> behind it and how do I take advantage of it? If not, any other
>> suggestions
>> for
>> why the antennas work so well?
>>
>>
>> Rudy N2WQ
>>
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