[Lf] Earthing the mast]

[Andre' Kesteloot]

Mike Dennison wrote:

> A few weeks ago there was a discussion about whether to earth
> masts, or leave them 'floating'.
>
> In the continuous search for more dBs I tried earthing my mast on
> Saturday.
>
> I have a 14m (45ft) mast attached to the brick wall of the house by
> 'T' and 'K' brackets, standing off about 300mm (1ft). Its base is
> 600mm (2ft) above ground level. The vertical part of the antenna is
> about 1m (3ft) away from the mast.
>
> I connected the mast to the wire which runs from the Tx to the earth
> stakes. I expected the capacitance between the mast and the
> vertical to change the tuning. The change was in fact very small, but
> the first thing I noticed was the variometer tuning became much
> more critical. The second thing was a 10 per cent increase in
> antenna current. Conclusion: the Q of the antenna had increased.
>
> I was still prepared to believe that I had simply added a capacitor
> from the antenna to earth, but when I checked the receive
> performance the signals improved by 1-2dB (tested by monitoring
> DCF and detuning until one of the 'S-meter' LCD blobs flickered,
> then noting  that the blob stayed on with the earth connected), and
> the local noise level reduced at the same time.
>
> Another effect, in the short time since I made this change, has been
> the antenna current has been stable. Before, it would vary by
> between 10 and 20 percent from one day to the next, depending on
> the weather, and I assumed this was absorption by trees.
>
> It seems that the mast/wall was acting as a resistor to earth,
> absorbing a different amount of RF from day to day.
>
> I also earthed the mast at the far end of my inverted-L and
> connected the two with a wire, but this had much less effect. This
> mast is already stuck in the mud at its base so was probably already
> earthy.
>
> What to do next?
>
> Mike, G3XDV (IO91VT)
> http://www.lf.thersgb.net