Envelope-to: dave@picks.force9.co.uk
Delivery-date: Thu, 17 Nov 2005 12:56:22 +0000
Message-Id: <5.1.0.14.0.20051117135923.012d1078@u0019445.kuleuven.be>
Date: Thu, 17 Nov 2005 13:59:28 +0100
To: rsgb_lf_group@blacksheep.org
From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
In-Reply-To: <6.1.0.6.2.20051115135604.01e10ae0@127.0.0.1>
References: <000901c5e9d2$c0cd9670$1f03210a@Hugh>
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 <1132001620.4378f95428c87@webmail.ukonline.net>
 <000901c5e9d2$c0cd9670$1f03210a@Hugh>
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Subject: Re: LF: Re: How measuring Ground conductivity ?
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At 13:56 15/11/2005 +0100, you wrote:
>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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