[Lf] [Fwd: LF: Ground Losses]

[Andre' Kesteloot]

James Moritz wrote:

> Dear LF Group,
>
> Some more info for the 'ground' loss database:
>
> As a follow on to the Puckeridge antenna experiments of a couple
> of months ago, I put up the same 42m long wire as I used for the
> 'small' antenna at Puckeridge, in my back garden, and made some
> measurements. The ground system in both cases was 4 x 1m
> copper pipes, spread out 2m around the antenna downlead.
>
> The soil at my QTH is heavy clay, overlying chalk that seems to be
> saturated with water (if you dig a hole, it will usually fill up). That at
> Puckeridge seemed to be identical. The QTH is surrounded by
> large trees on 3 sides, plus various houses and agricultural
> buildings. At Puckeridge, the small antenna was put up in an open
> field.
>
> At Puckeridge, the loss resistance was 25ohms. At home, this rose
> to 40ohms. I compared this to my usual LF antenna, which has a
> ground system using about 12 ground spikes spread all over the
> garden, plus pipes and mains ground in the house - loss resistance
> 50 ohms.
>
> You could argue that the low losses at Puckeridge might be due to
> the ground spikes being close to the main antenna earth mat,
> although to affect the loss resistance, only the ground very close
> to the antenna will have much effect. However, the slightly better
> efficiency of the small antenna compared to my usual antenna at
> my home QTH strongly suggests that actual loss in the ground is
> not the main factor - it was possible to position the 42m wire
> further from the trees than the two wires of my usual antenna, so I
> intend to experiment further along these lines.
>
> on 73kHz, the loss resistance of my usual antenna is about
> 100ohms. I have not tried the 42m wire on 73k yet.
>
> Incidentally, after taking reduced antenna current into account, the
> radiated signal from the 42m wire was about 3 - 4dB down
> compared to at Puckeridge. If one adds the loss of efficiency, the
> antenna radiates about 6dB less signal at home than it did at
> Puckeridge.
>
> The loss resistance measurements are not of high precision, due
> to the need to take into account the loss in the loading coil as well,
> but the trend is definitely real.
>
> I have previously observed that the loss resistance rises as the
> weather gets warmer, as has been reported by others, too. If
> anything, the ground has been getting wetter as we go towards
> summer, so this ought to bring ground losses down.
>
> Cheers, Jim Moritz
> 73 de M0BMU