Ian Jackson wrote:
In message ,
writes
Szczepan Bialek wrote:
Simply same of you do not know that "dipole" is a radiator and counterpoise.
A dipole does NOT have a counterpoise.
As I keep saying, I'm convinced that Szczepan is thinking of a situation
where a dipole fed directly with coax. He may have seen diagrams which
show this, and they have become fixed in his mind.
I think he is totally unable to understand that an antenna and a transmission
line are two different things.
Then, because the coax is (usually) grounded at the TX end, he believes
that the leg of the dipole, which is connected to the coax screen, is
also grounded - and therefore it serves the function of a counterpoise -
like you might use in a situation where the antenna is a directly-fed
end-fed wire situations, and it is not possible to get a good ground
connection.
In a way, Szczepan is sort of right. Consider the situation where a
dipole (no balun) is connected to the TX via essentially zero length
coax, and the TX chassis is not well grounded. [For example, possibly
there is a physical safety ground connection, but it is too long to be
effective at RF.] The 'ground' side of the of the dipole would indeed
function as a counterpoise, which might - or might not - radiate
effectively (depending on its height, its physical relationship relative
to the 'live' leg etc).
That does not change a dipole into anything other than a dipole.
Feeding an antenna with any transmission line ill suited for the antenna
will of course lead to unwanted currents which will radiate to some
degree.
However, the antenna is defined by the geometry of the antenna and the
transmission line does not change the radiation of the antenna unless
you are doing something really stupid like taping the transmission line
to one of the elements of the antenna, which changes the antenna
geometry.
Feeding an unbalanced load such as a ground plane with balanced line
will also lead to unwanted currents which will radiate to some degree,
but the ground plane antenna is still a ground plane antenna.