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Re: LF: Earthing the mast

To: [email protected]
Subject: Re: LF: Earthing the mast
From: "Hans-Joachim Brandt" <[email protected]>
Date: Mon, 5 Feb 2001 13:54:58 +0100
References: <3A7E870B.22556.5402A0@localhost>
Reply-to: [email protected]
Sender: <[email protected]>
Thank You for this description!
I would recommend: Keep both masts grounded.

73 Ha-Jo, DJ1ZB


Mike Dennison schrieb:
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





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