You can do it that way Bryan you just have to reverse the croc clips quickly
!! :-))
Cheers de Alan G3NYK
----- Original Message -----
From: "captbrian" <[email protected]>
To: <[email protected]>
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 <[email protected]>:
> 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"
<[email protected]>
> >To: <[email protected]>
> >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 <[email protected]>:
> >>
> >>>.
> >>>
> >>>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"
<[email protected]>
> >>>To: <[email protected]>
> >>>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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