----- Original Message -----
From: Herb Schoenbohm
Date: Thursday, July 21, 2011 2:10 am
Subject: Re: Topband: water saturated ground effect-MA160
To: BRYON PAUL n0ah VEAL
Cc: "topband@contesting.com"
> Paul, I was trying to suggest that with a good radial ground <BR>> the
> impedance variation should be less variable due to moisture. On
> your
> question, it all depends on the soil. Fresh water is an
> insulator of
> sorts. Depending upon whether your soil is acidic or basic this
> could
> get better or worse. I had an interesting installation at WIRA
> in Ft.
> Pierce, FL where the 1/4 wave vertical was out on a pier on the
> Indian
> River (salt water) with radials in the water and anchored to the
> river
> bottom. Still as the tide would rise and fall the base current
> would
> change accordingly. Now if the river were fresh water and the
> radials
> ran the same way, and since the fresh water is a much lower
> conductivity
> than the copper wire, a change in tide would have made much less
> difference, IMHO
>
What was happening, tide was changing length of "wire" between the feedpoint
and water surface. Radials submerged in the salt water only "work" (connecting
to water surface) to few inches below the surface, rest of radial wire length
below the water gets "chopped off" - water surface takes over the function of
ground plane. Height of feedpoint over water surface has slight effect on
pattern and adding more high current carrying radiator portion with tide
dropping and shifting impedance.
At the www.TeslaRadio.org site, there are bunch of wideband discone verticals,
sitting in salty marsh. Feedpoints are elevated about 4 ft, there is a wooden
"fence" around the base, about 15 ft from feedpoint. Radials are coming from
the feedpoint, to the top of the fence and then dropping into the salt water.
This allows to stabilize the current in the immediate vicinity of feedpoint and
minimize the tide effect. Those radio enginners back in old days new the stuff
without modeling software.
Yuri, K3BU
see you all at Tesla Radiofest BBQ this Saturday July 23
www.TeslaRadio.org
www.MVmanor.com
it is cooler in the mountains and the beer is soooo cool!
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|