On Jun 21, 10:30*pm, "Pete Bertini" wrote:
"You" wrote in message

...



In article ,
"Pete Bertini" wrote:

define "rf ground".

Something that provides a counterpoise for an unbalanced feedline
situation that doesn't result in RF energy being wasted to heat
earthworms, soil, etc. and radiates RF energy efficiently.

the ground radiates? *that's interesting.

so the raised radials on my 80m 4-square would be considered an rf
ground?

I would consider them to be an effective RF ground at their 1/4
wave resonant points, just as would a tuned artificial RF ground
used for stations at elevated locations.

Pete

Actually, a "GOOD" RF Ground will exhibit a very LOW Impedance across a
broad Frequency Spectrum, and NOT just at any single Frequency.... When
designing an RF Grounding System for a particular Site/Antenna System,
it is almost as important to know the Frequencies, and Bandwidths, to be
transmitted on, as it is to know the practical design of the Antenna
itself. Earth Conductivity has a much smaller effect than most folks
think.

Oh dear. What does this say about "Artificial RF Grounds?"
For that matter, is a tuned "artificial RF ground" a real *"ground" or part
of the antenna's radiation system?

Pete

its part of the 'system' but radiating or not can be debated.

There are a couple problems when talking about RF Grounds.

You can not equalize the rf voltage over anything that is an
appreciable fraction of a wavelength using any type or combination of
rods, radials, screens, or rings... it just ain't possible. any
ground system other than the fictional 'perfect' ground will have a
pattern of voltage peaks and nulls much like standing waves in 2 or 3
dimensions. therefor you can not call any particular point on the
ground system 'ground' for purposes of voltage measurements... nor can
you trust any particular point to be equal to any other point, so you
can get rf burns while standing on a 'ground' screen and touching a
coax shield or neutral or 'ground' power cable.

The whole purpose of the 'artificial' ground is to force one of the
voltage nulls to be where it will do the most good... if that means
you have problems with rf getting into your computer keyboard, or get
burnt by the mic when you swallow it, you can 'tune' the ground to
cancel out that effect locally... of course that means that there will
be changes in other places that may cause other problems, but at least
you won't get burned.

Now, on to the 'rf ground' as it applies to something you build under
a vertical radiator.... sorry, this will have to wait... just sleep
on currents going up the vertical having to be equal and opposite all
the currents flowing back into the shield side of the coax... no
matter where they come from, and imagine all the chances for currents
to be where you don't want them.