Envelope-to: dave@picks.force9.co.uk
Delivery-date: Tue, 15 Nov 2005 15:56:06 +0000
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Date: Tue, 15 Nov 2005 15:54:57 +0000
From: captbrian <captbrian@ukonline.co.uk>
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>
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Subject: Re: LF: Re: How measuring Ground conductivity ?
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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
> >
> 


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