Re: LF: Hoar-Frost and Antenna Losses

[Rik Strobbe <rik.strobbe@fys.kuleuven.ac.be>]

Tom

have a look at this :
http://thayer.dartmouth.edu/other/inductor/papers/hfdeice.pdf

It's a paper named "Using Dielectric Losses to De-Ice Power
Transmission Lines with 100 kHz High-Voltage Excitation"

73, Rik

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