Rick (long answer),
You are most likely mixing RF ground with a 'Mother Earth' ground. They
are quite different. The main reason is that RF does not behave like
low frequency AC or DC. You are not alone - that fact seems to mystify
and confuse many, many hams. I will try to give a conceptual
explanation. First understand that I use RF Ground as any point where
the RF voltage is zero (note that the RF current will be a maximum at
that same point). No other concept of RF ground has ever made any
sense to me.
With a balanced dipole antenna (center fed doublet), a point of RF
ground will occur at the midpoint of the center feed. That is where the
RF voltage crosses zero. If the radiator is fed with a parallel
transmission line, the currents on the two conductors will be equal an
opposite all along the feedline, so that effective RF Ground point is
carried all the way back to the shack along the transmission line.
If one uses coax to feed the antenna, a similar situation exists
*inside* the coax - due to skin effect, the inside of the coax shield
can be considered as a separate wire than the outside of the shield.
The currents on the center conductor and the inside of the shield will
be balanced (just like in the parallel transmission line). The problem
with coax is at the junction of the radiator and the shield. The RF
voltage (and current) on the inside of the shield sees two conductors at
that junction 1) the antenna wire, and 2) the outside of the coax
shield. A current balun installed at the antenna feedpoint will place a
high impedance on the outside of the coax shield while not interfering
with the balanced currents between the center conductor and the inside
of the shield. So, RF ground is maintained inside the coax - it is a
zero potential point that can be visualized as being midway between
those conductors. The item that seems to cause the most confusion is
that the coax shield can be at ground potential for DC and low frequency
AC, but it is *not* at ground potential for RF.
So, you do not need to create an RF ground for your dipole - it already
exists.
For a vertical with an elevated ground plane, a similar RF ground exists
midway between the vertical radiator and the ground plane (yes, the
ground wires radiate and are part of the antenna system - cancellation
of the ground wire radiation must be by the physical orientation so the
radiation cancels due to phase relationships). If a vertical radiator
is ground mounted, the earth takes the place of the ground plane - and
actual earth is not a really good conductor of RF, so we usually augment
that conduction by burying a lot of radials, the lengths are not
critical in those installations because we just want to improve the RF
characteristics of the real earth.
Bottom line is that I make the statement that an actual RF ground is a
property of the antenna system and is not to be equated to a Mother
Earth ground.
73,
Don W3FPR
Rick Dettinger wrote:
If I remember correctly, the base K2 came without the ground screw.
Its been a long time. I think the ground screw came with the ATU.
The K1 doesn't have a ground screw, even with the ATU. I am confused
about the use of an RF ground with a balanced antenna. One of the
advantages of a balanced antenna, verses an antenna that works with a
ground such as a vertical, is efficiency. If I use an RF ground with
a balanced antenna, am I losing efficiency. Especially if the ground
is mediocre? I don't want to put down 60 radials for my center fed
doublet. When I used my K1 or K2 with a battery and a balanced
antenna, I had confidence that most of the power was getting radiated.
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