John's observations are useful. A dramatic example happened to me many
years ago with a second story transmitter having a grounding wire that was
as short as possible: with a change of frequency, the grounding wire became
resonant and caused the transmitter to be very hot - I can still see the
small scar tissue where I touched a knob. The short term cure was to run a
longer grounding wire in parallel, which detuned the first wire.
If you use a reasonably balanced antenna (dipole, yagi, log-periodic,
.... ) it is unlikely that you will have a problem.
If you are to use a doublet fed with open-wire and fairly low power, an
old Johnson Matchbox will be an ideal way to keep your transmitter happy.
Keep us posted. 73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
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"JOHN PASSANEAU" wrote in message
...
Hi Danny:
You are of course correct, but with RF in the shack problems levels are
important. If the level of RF is below some threshold it causes no harm.
Almost all Ham stations operate just fine with low levels of unbalance
and other defects in the antennas.
Just for interest sake I ran some numbers on a model ground system. Let's
assume you have a perfect ground system and you connect to it from the
shack on the second floor using 12' of #6 wire. And it runs in a straight
line, no bends or curls. The self inductance of that wire is about
56.22uHy.
So what will be the reactance of that wire at 3.5 MHz? Doing the math I
get 1,235.7ohms. At the other extreme 28MHz, I get 9,886.52ohms. These
are numbers that hardly make me confident that I have any kind of a RF
ground.
By the way at 60Hz the reactance is 0.021ohms that I think is a good
ground.
Please excuse me for harping on this, but I run the electronics shop in
the Physics dept at Penn State University. I'm constantly seeing many
meter long thin wires tied to some cold water pipe or something in a lab
that is supposed to get rid of all the high frequency noise in some
experiment and it has no chance of helping. If physics grad students have
problems understanding grounding it's no wonder that Ham's do too.
John Passaneau W3JXP