[Lf] grounding in a well ?

[Andre' Kesteloot]

Stewart Nelson wrote:

> Hi all,
>
> Thanks to everyone who responded to my query about using a well for
> grounding.  The answers were about evenly divided between "it's
> wonderful" and "it's useless" :)
>
> I suspect that both might be true, depending on how far down the
> water is.  In my case the water comes up almost to ground level,
> so it seemed promising, and I attempted to make an impedance
> measurement at 180 kHz.  I used an audio generator with the hot
> lead connected to the well casing, and the cold attached to a
> shovel driven into the ground about 50 feet away.  A current
> probe showed that I could get about 20 mA p-p to flow.
>
> At first, I connected the scope ground to a second shovel, placed
> about 50 feet away in the opposite direction, and connected the
> channel 2 input to the well.  I saw almost no trace of the 180
> kHz.  There was about 1.5 volts p-p of (badly distorted) 60 Hz.
> It makes sense to see some AC, because the house electrical system
> is grounded to the water piping, but, if my ground resistance
> estimate of 0.5 ohms is accurate, then about 1 A RMS is flowing.
> Is this plausible?
>
> Then, I put a small capacitor in series with the scope to eliminate
> the 60 Hz.  Now there is about 0.5 V p-p of RF.  It's AM broadcast.
> Again, I would expect some, but this much is inconsistent with
> the impedance I measured at 180 kHz, below.  Is is possible that
> the house wiring picks up the RF and couples it to the well?  Or
> that the well impedance is many times higher at 1 MHz than at 180
> kHz?  Or is my impedance measurement grossly invalid?
>
> Next, I rigged a parallel L-C across the scope, tuned to 180 kHz,
> with a suitable series resistor.  Now I can see the signal clearly.
> It's about 100 mV p-p, so the impedance is about 5 ohms.  There is
> more than 45 degrees of phase shift (voltage leading).  A rough
> guess is that there is 3 + j4 ohms.  If valid, this is probably
> much better than ground radials.  But I don't want to go to the
> effort of erecting an antenna here if this is bogus - there are
> better locations if radials are needed.
>
> Also, I noticed that the voltage waveform (using the current
> for sync) appeared as two waves about 10 degrees apart.  Closer
> inspection showed that the phase was varying at a 120 Hz rate.
> Could the AC line current flowing cause the RF well impedance to
> change?  Doing something to the generator path?  Or is this some
> artifact of my test setup?  I don't see the effect when a resistive
> test load is used.
>
> Finally, thanks to Dick Carroll for warning me about possible
> lightning damage to the well pump.  But I am also worried that
> a lesser ground could increase the chances of fire or damage to
> other equipment.  How are most lowfer antennas grounded for safety?
>
> Any ideas appreciated.
>
> 73,
>
> Stewart  KK7KA
>
> To unsubscribe, send to MAJORDOMO at qth.net "unsubscribe lowfer" (Do not
> send to list!!) Send on list submissions to lowfer at qth.net
-------------- next part --------------
An embedded message was scrubbed...
From: "Stewart Nelson" <sn at scgroup.com>
Subject: Re: [Lowfer] antennas
Date: Tue, 1 Feb 2000 20:02:55 -0800
Size: 4434
Url: http://atanasoff.rf.org/pipermail/lf/attachments/20000202/ff79bffe/attachment.txt