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Re: LF: Hoar-Frost and Antenna Losses

To: [email protected]
Subject: Re: LF: Hoar-Frost and Antenna Losses
From: Rik Strobbe <[email protected]>
Date: Mon, 13 Dec 2004 12:34:45 +0100
In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Hi Tom,

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 "magnetic loss" while at the antenna it is the dielectric loss that counts.
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 ;-)

73, Rik  ON7YD

At 19:18 12/12/2004 +0100, you wrote:
Dear LF Group,
 
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.
 
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.
 
Some calculations showed the following values for the total loss resistance of the antenna system:
 
-  no frost, normal conditions:  R = 24 Ohms
-  frost:  R = 18 Ohms
-  hoar-frost:  R = 31 Ohms
 
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.
 
Anyone with a good idea?
 
73,
Tom, DK1IS
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