Message-ID: <17550.200101291220@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Mon, 29 Jan 2001 12:24:30 +0000
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Subject: LF: Earth Rods / Spectrograms
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Reply-To: rsgb_lf_group@blacksheep.org
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Dear LF Group,

I found an easy way to drive in earth rods made from copper water 
pipe is like this: I found a steel rod of a slightly bigger diameter than 
the pipe, put a point on the end, and hammered it in to the ground. 
When it is in deep enough, it can be pulled out, and the copper pipe 
tapped into the hole. When driving the steel rod, it helps to pull it 
out occasionally, and pour some soapy water into the hole. This 
makes it easier to drive in, and easier to get the rod out 
afterwards. You need to fix something to the rod to hold on to when 
you are pulling it out. I used "Mole grips".

As well as AGC effects, another thing that will break up lines on a 
spectrogram display is any kind of limiting or overloading in the 
receiver or soundcard A/D converter. This is important when you 
leave the system running for several hours, and signal or noise 
levels change quite a bit. It's worth spending some time finding a 
gain level that gives signals well over the receiver noise level, but 
at least 10 or 20dB below the onset of overload. 

Cheers, Jim Moritz
73 de M0BMU