Hi Stefan,
> > Hmm, my understanding is that a DC measurement won't be too useful as
> > it will suffer from polarisation problems. When you do a DC
> > measurement, try to reverse the polarity and let me know what happens
> > to the resistance you are measuring compared to the previous polarity.
> >
> I know about the effect of an extra voltage drop on the surface of an
> electrode into soil. Thus i recommend to use a larger voltage. Why do
> you expect a different DC resistance when changing the polarity?
> I can do that test you suggested but i don't expect a difference. It
> could be interesting to rise the voltage from 0 to say 50V in small
> steps and note the current and then draw a graph. Then you would see the
> nonlinearity. I would expect that it is only visible below 10 V.
What I was thinking is the induced polarization phenomenon in
geophysical ground measurements. It has to do with mobilization of
ions near the electrodes in the ground due to the constant electric
field which results in a measurement that changes with time. If the
time constant is low, perhaps that's not a problem but until you
check, you can't be sure. I think it's worth while doing that polarity
change next time you are doing measurement and report back on your
findings. Do that test you suggested, from 0 to 50 volts and then
repeat it using 0 to - 50 volts and plot them on the same chart..
> Very well. Cucumber, a word i had to learn. Do you know how to bridge
> the PA to get another 3 dB of output power?
Yes, it's quite simple however I will need one isolating transformer
as the output is given from the two non-grounded output terminals of
the two channels. That shouldn't be a problem. Alternatively, I can
ensure that no part of the loop is grounded, however that's more
difficult.
73, Dimitris VK2COW
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