[TowerTalk] Anomolous ground conditions
w8ji at contesting.com
Mon Nov 7 18:45:25 EST 2005
>I moved to my mountaintop QTH in New Mexico, and before I
had any towers
>erected I put up 20 and 40 meter dipoles. They weren't
very high - in
>the 20-30 foot range. To my surprise, I couldn't get the
SWR below 2:1
>at any frequency. Did the usual things - changed coax,
>lengths, changed SWR meters, etc. Nothing would get them
close to 50 ohms.
What balun are you using? Are the antenna in the clear?
>The real reason I care is to try to improve my 160 meter
signal. I have
>a full-size vertical, with 10 ground radials. To Europe,
it feels like
>it's down 6-10 dB from my 160 antenna at my Colorado QTH
>sloper, good ground conditions).
That's not much of a ground system. Also, you are just going
by a feeling. To be truthful, most people can't feel several
dB if it is biting them on the rear like a Pit Bull.
>Anyone care to speculate on what my ground looks like to
RF, and why it
>would appear that a low dipole would have a radiation
resistance of ~25
>ohms (or ~100 ohms). If the ground was lossy, shouldn't
>resistance be closer to 50 or 75 ohms ?
Which is it? 25 or 100? That would be important to know.
>Unrelated side note: I occassionally hear hams on the air
>how wonderful it would be to have an antenna farm on a
You hear Hams talk about all kinds of things, that's mostly
what we do. Talk. ;-)
>USA's 2nd largest open-pit copper mine is 2 miles from
here. My wife is
>an engineer there. She says that at best, this mine has
2% copper in
>the ore. I can't believe that rock with 2% copper would
>discernable effect on RF.
It doesn't. However, if you extract the copper and lay it on
the ground in a sheet.....
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