[TowerTalk] Vertical in pond

[K4SAV]

N3OX wrote: An important thing for the original poster: the lake has to 
be very large
for this to work,...............

Also it has to be very deep.  Those gain numbers you got from EZNEC 
assume an infinitely deep lake.  Since the depth of penetration in fresh 
water is about 156 ft (independent of frequency in the HF range), unless 
you live on Loch Ness those numbers are probably optimistic.

Jerry, K4SAV

Dan Zimmerman N3OX wrote:
> On Tue, Mar 17, 2009 at 9:24 AM, Pete Smith <n4zr at contesting.com> wrote:
>
>   
>> Isn't it more likely that the ground characteristics in that location are
>> more favorable than in the previous one?  I can imagine ground well
>> saturated with fresh water as having a sufficient quantity of ions in
>> solution to improve its conductivity considerably.  The fresh water itself,
>> on the other hand, probably doesn't matter.  Or does it?  Anyone have
>> anything beyond anecdotal experience to pass on?
>>     
>
>
>  There should be less field cancellation at very low angles for a vertical
> that looks out over fresh water... look up "Pseudo Brewster Angle" in your
> favorite antenna book.
>
> If I change the earth dielectric constant in EZNEC from 13 to 80 (soil to
> water) underneath a 1/4 wave vertical on 40m, I pick up about 7dB at 1
> degree elevation and 5dB at 5 degrees elevation.
>
> Also, a lake is nice and flat without any scatterers or obstructions.  I
> would imagine that the PBA effect plus lack of scattering obstacles
> intercepting low angle radiation could give you a pretty serious boost.
>
> Of course, some of this would happen even if you were backed away from the
> lake a couple wavelengths. You'd have to look at the geometry in detail to
> see what you might expect advancing from 100m away from the lake to right up
> on the lake, and you have to qualify what stations you're interested in and
> what the takeoff angles to them are.  High angle enhancement is there, but
> it's only to the tune of a dB or two up at 30-40 degrees.
>
> A test for whether or not it's a PBA and reduced ground clutter effect would
> be that you only get enhancement for paths that go over the lake.  Back
> toward land should have no effect.
>
> Improved earth conductivity would give you a boost in all directions.  I'd
> think by the time you got to "lots" of radials, though, you just wouldn't
> have more than a dB or two to pick up even by copper plating the ground,
> even with liberal interpretations of "lots"
>
> An important thing for the original poster: the lake has to be very large
> for this to work, many tens of wavelengths  for the very low angle
> radiation, probably at least a couple for any useful DX angles.  A "pond"
> probably wouldn't hack it.  It only works if the ground reflections that
> correspond to the desired elevation angle paths happen out on the water.
>
> Add that to the fact that it's a pain to install and maintain an antenna
> that's in a pond, and it's not worth it.  If you can mount your vertical on
> the edge of a freshwater lake, it's probably useful, but you wouldn't
> necessarily want to mount it in the middle of one, unless you had a really
> conveniently located small island (less than a wavelength or so in diameter)
>
>
>
> 73
> Dan
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