[Lowfer] Beverage ground question

[John RABSON]

Hello Stan,

I will have a think about rainfall monitoring.  Given that it would take time for the water to soak its way through, I could perhaps check the resistance two or three times a day on a regular basis.  I used to use an Amstrad luggable PC (portable if you have the muscles) as an experiment controller, but it has severe limitations (4.7 MHz 8086 CPU, 512K Ram and two 720K floppy disks) and the A: drive has just died.

My resistance meter only works on 980Hz.  I have inherited some General Radio gear which should enable me to measure the impedance at 136kHz, but I have not yet sorted out a suitable source.  My existing signal generator does not provide enough output.

The three existing electrodes are in a triangle.  Chris, G4OKW, has sent me GF Tagg's book on earth resistance and it looks as if there is not an enormous difference between three in a line and three in a triangle.  In any case, I have enough real estate to be able to drive another three electrodes with similar spacing to the existing ones should I need to do so.

73
John F5VLF

*********** REPLY SEPARATOR  ***********

On 28/12/2007 at 08:26 Stan wrote:

>Hello John,
>
>Yes, quite interesting. Reasonably small variation. I also suspect the 
>water content.
>
>The only way, I can immediately think of, to qualify this effect, is to 
>continuously monitor the
>earth to electrode system resistance, before, during, and after a rain 
>storm.
>Would be nice to monitor rate of rain fall or total rainfall.
>
>Can you vary the frequency of the test ? Some testers like a hand crank 
>Biddle
>can vary the freq according to the speed of cranking.  If there is 
>inductance in the system
>the impedance will vary. If only resistive, the resistance (impedance)
>will be the same for any test freq, or cranking speed.
>Less inductance the better, for a lightning protection system and an RF 
>ground.
>
>Other ground testers like the Associated Research  Vibroground unit uses 
>a mechanical multivibrator
>and batteries to set the test freq. More modern solid state units are 
>probably much more freq stable.
>Just saw a Vibroground on ebay, for 1$, with no bidders, was a 3 wire 
>tester.
>Really obscure test equipment, Who does ground testing today ???
>Vendors: Biddle, AEMC, AR...
>
>Is your earth electrode system in a triangle configuration or in line ?
>Probably would not matter because of the very decent separation.
>
>Stan, W1LE   FN41sr   Cape Cod
>
>
>
>
>John RABSON wrote:
>> On 26/12/2007 at 17:05 Stan wrote:
>>
>> [ ... ]
>>
>>   
>>> As an exercise measure your ground rod system resistance in the summer
>>> and then compare to winter conditions.
>>> A good system will have the same resistance in all seasons.
>>>     
>> You might find the following of interest.
>>
>> The ground rod system here consists of three 4 foot rods 20 feet apart
>in at least 10 feet of sandy soil, underneath which is limestone/granite. 
>Over the past 2 1/2 years their combined resistance has varied a little
>(measurements at 980Hz):
>>
>> Q2: 22 to 27 ohms
>> Q3: 20 to 23 ohms
>> Q4: 23 to 31 ohms
>>
>> No figures for Q1.
>>
>> I suspect the variation is related to rainfall, but I have no firm
>information on this.  Would anyone like to comment, please?
>>
>> 73
>> John F5VLF
>>
>>
>>
>>
>>
>>
>>
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