Re: LF: EARTH RESISTANCE

["Dave Pick" <g3yxm@wireless.org.uk>]

Ralph

 

You'd have to use an isolating transformer here because one side of our mains is earthed. Sounds exciting though, I remember testing my earth system when I was a lad, by connecting the live side of the mains to it via an electric fire and seeing how bright it glowed! (not the earth - the fire...)

 

Dave G3YXM

----- Original Message -----

From: Ralph Lane

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, December 17, 2002 12:39 PM

Subject: Re: LF: EARTH RESISTANCE

Sorry about that. Here is the test of my message:

 

Ralph

 

"Ground Conductivity Test" is from the ARRL Antenna Handbook...

The book I have is from 1994....and it is on page 27-35 that's chapter 27 page 35........

Conductivity Soil, Measurement of....

It takes 4 rods.......9/16" diameter and 14 inches long these 4 rods are driven into the ground 18 inches apart in a straight line......drive them in 12 inches...

One side of the 120 AC line to a 100 watt light bulb...the other side of the bulb to a 14.6 ohm resistor.........they say to make up the resistor by paralleling 5 of them...3 of which are 68 ohm 1 watt....the other 2 are 82 ohm 1 watt......then the other end of the resistor goes to rod #1 .......the other side of the AC line goes to the farthest rod.....

You now have two AC voltage test points......V1 is across the resistor. V2 is voltage measured between rods #2 and #3.....

In general these two voltages they say should be from 2 to 10 volts......

Formula for calculation is......

C = 21 x V1/V2
 

This gives you the Millisiemens per meter

----- Original Message -----

From: Dick Rollema

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, December 17, 2002 5:35 AM

Subject: Re: LF: EARTH RESISTANCE

To All from PA0SE

Mike, G3XDV, wrote:

I think this is why people are confused. I believe that Dick measured

"system loss", which includes all losses except inductor loss. Calling it
"earth resistance" simplifies the situation too much. Plainly a wet
environment will increase leakages.

I indeed measured the total resistance of the aerial system (minus the coil loss) as I have explained in my e-mail. I agree with Mike that "system loss" would have been a better _expression_ than "earth resistance".  

Has anyone measured earth resistance alone under different conditions? If I
recall correctly, this can be done with three earth stakes and Kirchoff's
laws.

Indeed, but it usually done at 50Hz. To be meaningful at LF the measurement should be performed at an LF frequency. But I'm afraid that will not be so simple.

73, Dick, PA0SE