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LF: Hoar-Frost and Antenna Losses

To: [email protected]
Subject: LF: Hoar-Frost and Antenna Losses
From: "Thomas Koelpin" <[email protected]>
Date: Sun, 12 Dec 2004 19:18:34 +0100
Cc: [email protected]
Reply-to: [email protected]
Sender: [email protected]
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?
Tom, DK1IS
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