Re: high earth resistance

dansawyeror <dansawyeror@xxxxxxxxxxx> wrote in
news:lMednY_woZ84NYbbnZ2dnUVZ_sWdnZ2d@xxxxxxxxxxx:

Owen,

Are you referring to the coil alone? You are correct the coil accounts
for a significant part, probably between 4 and 8 Ohms.

I don't recall that you have told us where the coil is located, and I am
not going to build a model to discover something that is relevant and
that you could have told us.

You have told us the coil had an "impedance" of 60uh. If it had an
inductance of 60uh, it would have an impedance of 1500/Q+j1500 where Q at
3.9MHz for a practical coil is likely to be above 100 and less than 300.
The resistive component of the coil has to be referred to the feedpoint
so that you can deduct it from the total feedpoint Z. The best way to do
that is your NEC model.

You should be able to form a better range for the equivalent coil loss at
the feedpoint than you stated above (since you seem to have the means of
measuring the coil and inserting the values in your model).

I am measuring real values between 52 and 56 Ohms with 0j. This varies
mainly with moisture.

So let's say the total antenna is 12 Ohms. If the measured value is 52
that says the ground is 40. This puts us back to the original
question: why is the ground so high?

You also previously said "... Even if the antenna were 6 to 8 Ohms the
ground loss would be at least 42 to 44 Ohms."

I read this to mean total system R is 50 ohms.

In this post it is reported between 52 and 56.

The other issue that Frank raised is the elevated feedpoint and whether
you modelled that correctly. The radiation resistance you quoted seems
(without checking) reasonable for a short monopole over ideal ground, but
one expects it would be higher for an elevated feed point. Have you
modelled the antenna you built, or have you build an antenna you cannot
model accurately and are applying model results incorrectly to the thing
you have built?

Though you see only one question, "why is ground 40 ohms", you haven't
disclosed enough information in your posts to convince me that it is 40
ohms. If you ask the wrong question, you might not get a useful answer.

Is ground 40 ohms?

Owen
.

Relevant Pages

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  • Re: high earth resistance
    ... he impedance of the coil measures about 60 uH. ... The resistive component of the coil has to be referred to the feedpoint so that you can deduct it from the total feedpoint Z. The best way to do that is your NEC model. ... So let's say the total antenna is 12 Ohms. ...
    (rec.radio.amateur.antenna)