[RFI] Ground Question
ka5s at earthlink.net
Mon Feb 3 17:27:38 EST 2003
I don't believe this is much better than a plain wire. And that is not
really very good. On frequencies where the ground conductor is a quarter
wavelength long, or an odd multiple of a quarter wavelength, it will
actually ISOLATE the station from ground, and on most other frequencies
will look like some value of inductor or capacitor between your station and
Some people use what's called an "artificial ground." This is actually a
tuner that cancels out the inductive or capacitive reactance of ground
wire, and puts a low-impedance point at its connection to your operating
position. That's fine -- but by maximizing current in the wire, it also
insures it will radiate and maybe interfere with devices it passes near.
While you must have a powerline ground, I feel that an RF ground for
elevated ham-shacks is better had by attaching ones' operating ground to a
large metal object. Its capacitance to Earth should large enough that very
little voltage would be present between it and ground. A four foot by
eight food sheet of aluminum or similarly sized object(s) might do the job.
Tuned counterpoises are good; a quarter wavelength wire has a low impedance
at the station end, and one or preferably two for each of the lower bands
band, plus a smaller metal sheet counterpoise as above, can get rid of RF
problems in your shack.
The reason for using TWO counterpoises is, you run them in opposite
directions, and whatever one radiates is be cancelled at any decent
distance by the out-of-phase radiation from its mirror-image twin.
Counterpoises do not have to be straight, and if you can't get a quarter
wavelength in the shack, may also be tuned with an artificial ground. But
do try to keep them away from susceptible devices.
> [Original Message]
> From: <STRutledge at aol.com>
> To: <rfi at contesting.com>
> Hi folks. My shack is on the second floor of my house. No other
> had the same situation years ago in another house, another city. I was
> getting started in the hobby and several "old timers" told me about a
> of getting a good RF ground on the second floor. It involved using
> capacitors on a piece of RG-8U. You installed one at the shack and at
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