Envelope-to: dave@picks.force9.co.uk
Delivery-date: Tue, 15 Nov 2005 16:02:19 +0000
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From: "Alan Melia" <Alan.Melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
References: <000a01c5e938$ec8c8680$0400a8c0@router> <000501c5e93d$83feadf0$1f03210a@Hugh> <1132001620.4378f95428c87@webmail.ukonline.net> <000901c5e9d2$c0cd9670$1f03210a@Hugh> <6.1.0.6.2.20051115135604.01e10ae0@127.0.0.1> <1132070097.437a04d10e22e@webmail.ukonline.net>
Date: Tue, 15 Nov 2005 16:00:33 -0000
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Subject: Re: LF: Re: How measuring Ground conductivity ?
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You can do it that way Bryan you just have to reverse the croc clips quickly
!! :-))
Cheers de Alan G3NYK
----- Original Message -----
From: "captbrian" <captbrian@ukonline.co.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: 15 November 2005 15:54
Subject: Re: LF: Re: How measuring Ground conductivity ?


> Got it . Thanks both. You meant tens of metres - I thought 10s was ten
times an
> algebraic symbol s and didn't know what s represented LOL !!
>
> Its the temp. here that fries the brains.  Guess who tried to measure dc
> resistance between two rods in seawater with an m/ohm meter but didnt stop
to
> think that different metals for the rods generated a voltage which
confused
> everything. Back to the Budweiser head clearing cure.
>
> Bryan
>
> Quoting Dick Rollema <dickrollema@casema.nl>:
>
> > Hello Bryan,
> >
> > The earth resistance is frequency dependent.  Measurement at 50Hz says
> > nothing about the value at 137kHz. For more info  consult ON7YD's web
site:
> > http://www.qsl.net/on7yd/136khz.htm.
> >
> > I measure the earth resistance by inserting an RF bridge between the
bottom
> > end of the loading coil and the earth connection.  Then I  tune the
> > aerial/earth system to resonance in the LF band.  The bridge then
> > measures  the real part of the impedance of the system (so a bridge that
> > cannot measure  reactance is sufficient, for instance a simple homemade
> > noise bridge).
> >
> >  From the value so obtained I subtract the loss resistance of the coil.
> > This has been determined by measuring its inductance and  Q.
> >
> > The remaining value is the earth resistance by a good approximation. Of
> > course  loss and radiation resistance of the aerial itself are also part
of
> > the measured resistance. But these contributions are so small as
compared
> > to earth and coil resistance that they can be ignored.
> >
> > I find for my location an earth resistance at 137kHz of about 22 ohms in
> > winter. During summer it is somewhat higher and also when the earth is
wet
> > with rain.
> >
> > 73, Dick, PA0SE
> >
> >
> >
> > At 11:52 15-11-05, you wrote:
> > >Hello Bryan,
> > >Yes. 10s is twenty or thirty meters.
> > >I designed and built a bit of kit for the purpose of doing some
> > >archeological ground resistance surveys, (although in the end we were
able
> > >to use professional
> > >equipment from the Kent Archeological Society). I tried a frame with
four,
> > 4
> > >inch nails spaced 0.33m apart, in a line, and aerated the the back
garden
> > >with it. I found it quite a good random number generator from about 10
ohms
> > >to 60 ohms.
> > >
> > >I remade the frame with two nails spaced 1 metre apart, one measuring
and
> > >one driven, and using a long cable placed the other two probes well
outside
> > >the area being surveyed. This gave a much more consistent reading of
about
> > >10 ohms, except near the garden path where the reading was higher. This
is
> > >the configuration usually employed by archeologists as it is supposed
to
> > >"see" deeper into the soil.
> > >
> > >My measuring current was 1mA and the polarity reversed at 66Hz.
> > >
> > >You are right that the reading doesn't seem to vary much with probe
> > >spacing - a fact which still amazes me.
> > >My, very limited, knowledge comes mostly from the excellent book
"Seeing
> > >beneath the soil" by Anthony Clark.
> > >
> > >But as John has already observed, the parameter that we are measuring
has
> > >only to do with the ground rod effectiveness, and is not a measure of
RF
> > >losses.
> > >73
> > >Hugh M0WYE
> > >
> > >----- Original Message ----- From: "captbrian"
<captbrian@ukonline.co.uk>
> > >To: <rsgb_lf_group@blacksheep.org>
> > >Sent: Monday, November 14, 2005 8:53 PM
> > >Subject: Re: LF: Re: How measuring Ground conductivity ?
> > >
> > >
> > >>What does s stand for as in 10s of meters ? *(Presumably metres)*
> > >>
> > >>
> > >>I thought distance apart made no difference in homogenous soil ?
> > >>
> > >>Bryan (Floating in a boat on sea-water )
> > >>
> > >>Quoting Hugh M0WYE <m0wye@thersgb.net>:
> > >>
> > >>>.
> > >>>
> > >>>However I got similar readings to you - around 10 ohms - with moist,
> > >>>garden
> > >>>soil.
> > >>>
> > >>>I found the most repeatable readings were when one current and one
> > >>>voltage
> > >>>probe, 1m apart, were seperated by 10s of meters from the other
pair - as
> > >>>is
> > >>>
> > >>>used for archeological ground resistance surveys.
> > >>>
> > >>>73
> > >>>Hugh M0WYE
> > >>>
> > >>>
> > >>>----- Original Message ----- From: "Uwe Wensauer"
<uwe.wensauer@gmx.de>
> > >>>To: <rsgb_lf_group@blacksheep.org>
> > >>>Sent: Monday, November 14, 2005 4:31 PM
> > >>>Subject: LF: How measuring Ground conductivity ?
> > >>>
> > >>>
> > >>>To discuss
> > >>>
> > >>>Measure ground conductivity.
> > >>>
> > >>>
> > >>>I placed two stainless- steel rods ( 3mm dia ) whithin a distance of
7
> > >>>Meters apart abt 80cm deep into soil
> > >>>
> > >>>Powered with 50 Hz.
> > >>>In series with the electrodes is a 10 Ohm resistor. In order to
measuring
> > >>>current, I measure the voltage drop across resistor.
> > >>>
> > >>>Depending on weather I got 8 Ohm / m = 125mS
> > >>>
> > >>>Is this measurement setup ( proceeding ) correct ?
> > >>>
> > >>>Please correct me.
> > >>>
> > >>>Uwe, DK1KQ
> > >>>
> > >>>
> > >>>
> > >>
> > >>
> > >>--
> > >>
> > >>
> > >>----------------------------------------------
> > >>This mail sent through http://www.ukonline.net
> > >
> >
>
>
> --
>
>
> ----------------------------------------------
> This mail sent through http://www.ukonline.net
>