[Lf] Ground Losses

[Andre' Kesteloot]

Steve Rawlings wrote:

> Laurie G3AQC wrote:
>
> > I have just measured my TX ant impedance(R term) and it is 120 ohm!
> > much higher than I originally thought.  It is of course all ground
> > loss . . . .
>
> With the simple verticals which I use on 136 kHz, I have always tried to
> minimise the proximity between the radiator itself and earthy objects
> such as our house; the garden fence; and nearby trees.  From earlier
> contributions to this Reflector (thanks are due to Peter Martinez G3PLX,
> and others), I learned that the parallel loss caused by the proximity
> between the radiator and lossy ground translates into a
> series-equivalent resistance - which, in turn, contributes to the [120
> ohm] "ant impedance".  [I hope I have learned my lessons well, Peter!]
>
> So improvements to your ground system may help, but it might also be
> worth taking another look at your antenna to see whether there are
> opportunities for increasing the distance between your antenna system
> and nearby (earthy) structures.
>
> > . . . .  I wonder whether anyone can offer me comparitive
> > figs for impedance and details of ground systems?
>
> Before pruning trees in my neighbour's garden:
> **********************************************
> ANTENNA CONFIGURATION      WET DAY     DRY DAY
> 12 m vertical              160 ohm     130 ohm
> 20 m vertical              130 ohm     100 ohm
>
> After pruning trees in my neighbour's garden:
> **********************************************
> ANTENNA CONFIGURATION      WET DAY     DRY DAY
> 12 m vertical              130 ohm     100 ohm
> 20 m vertical              100 ohm     75 ohm
>
> Ground system
> *************
> Shack earth is isolated from the antenna ground connection using a
> matching transformer.  'Cold' end of transformer secondary winding is
> connected to outside water tap.
>
> For more information, see:
> http://www.alg.demon.co.uk/radio/136/experi_vert.htm
>
> The trees (prior to pruning) can be seen just behind (apple tree), and
> to the right (flowering cherry tree), of my vertical antenna at:
> http://www.alg.demon.co.uk/radio/136/pictures/expvert1.jpg
>
> Regards to all,
> Steve GW4ALG