Message-Id: <5.1.0.14.0.20041213122834.022ec128@u0019445.kuleuven.be>
Date: Mon, 13 Dec 2004 12:34:45 +0100
To: rsgb_lf_group@blacksheep.org
From: Rik Strobbe <rik.strobbe@fys.kuleuven.ac.be>
In-Reply-To: <002b01c4e076$ffa85080$d47cb9d9@pc>
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Subject: Re: LF: Hoar-Frost and Antenna Losses
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Hi Tom,<br><br>
few weeks ago the item of wet wood in/near a loading coil was discussed
and it seemed to increase the losses. But these would be &quot;magnetic
loss&quot; while at the antenna it is the dielectric loss that
counts.<br>
For the data you give it can conclude that the loss increased by 13 Ohm
(from 18 to 31 Ohm), so if you assume that this extra 13 Ohm is caused by
the ice on the antenna wire this would mean that the ice dissipates about
100 Watt. Maybe enough to melt the ice in QRSS10000 mode ;-)<br><br>
73, Rik&nbsp; ON7YD<br><br>
At 19:18 12/12/2004 +0100, you wrote:<br>
<blockquote type=cite class=cite cite><font face="arial" size=2>Dear LF
Group,<br>
&nbsp;<br>
last saturday morning we had the first hoar-frost this year at -6 degree
centigrade. All the trees and bushes in the backyard looked beautiful and
so did my 13-m-Marconi-antenna. Feeder and 33-m 4-wire-topload were
coated by fragile white needle crystals rising the wire diameter from
normally 1 mm to 4 or 5 mm.<br>
&nbsp;<br>
Switching on the TX with te usual settings the antenna current had
decreased from the normally 4.7 A (at frost) to 2.75 A! The antenna
capacity remained nearly unaffected (about 660 pF), but tuning the
loading coil showed a much broader maximum than without hoar-frost.<br>
&nbsp;<br>
Some calculations showed the following values for the total loss
resistance of the antenna system:<br>
&nbsp;<br>
-&nbsp; no frost, normal conditions:&nbsp; R = 24 Ohms<br>
-&nbsp; frost:&nbsp; R = 18 Ohms<br>
-&nbsp; hoar-frost:&nbsp; R = 31 Ohms<br>
&nbsp;<br>
According to some other measurements and observations these values should
be rather realistic. The difference between no-frost and frost is well
known and should mainly arise from the reduced losses in the greens - but
where do the additional losses at hoar-frost come from? Could the
hoar-frost be a lossy dielectric? There were neither visual corona
effects nor seemed the hoar-frost be melted by the antenna current.
Sunday morning it disappeared on itself and the antenna current rose
again to the usual 4.7 A at -3 degree centigrade.<br>
&nbsp;<br>
Anyone with a good idea?<br>
&nbsp;<br>
73,<br>
Tom, DK1IS</font></blockquote></html>