L. Fiar said:
I see your problem, it seems to be about perception. The antenna
signal does use a ground, and that ground is part of the antenna
system... you just have to recognise it.
A loop antenna should be easy. Being balanced, it does not have a
ground, the two ends are equal but opposite and DC coupled.
The basic dipole antenna is also balanced, with two sections, each
having an equal but opposite signal upon it.
With the ground plane antenna, this may appear to have just a single
vertical element, but has an image reflected in the ground. The
reference point is the ground.
Your problem is in the concept of that ground, which may be true
ground or an artificial ground made up of a plate, radials, etc.
In the case of a car, the vehicle body is that ground. There are
antennas that have radials pointing out from the base of the
antenna - this is then the ground.
Efficiency is traded off against practicality and, in some cases, the
ground may be as small and simple as the radio ground. Not the most
efficient situation, but practical for portable equipment.
There are several radio handbooks available, which may go into more detail
on RF radiation, propagation, and antenna theory. The Internet is fine, but
nothing beats a good technical book.
Believe me I have looked in books, they do not have
what I am asking. Even the link posted here talks
about antennas but does not answer my question.
Again, I have seen many interesting
answers here so I will reply here rather than reply to
all the senders. Firstly people seem to be talking about
loop antennas. Can we get a fix on terminology, is
a loop antenna the same as an fm telescopic antenna
because if it isn't then sorry but I am not really
interested in loop antennas.
Now, let me explain, ... if you connect a coax cable
to a t.v. vhf antenna, the antenna has two points and
this is very sensible, since the voltage is induced on
the two ends of this ellipse-like loop. Now, ... with
my fm radio there is this piece of extendable antenna
and it seems that there is one wire coming out of it
if one opens the cover and looks inside. Supposing
I wanted to connect a coax to this antenna, I have
only one wire, this is my question, where is the other
wire because a voltage must be between two wires.
Now, ... I think your answer was that the circuit
board, being made up of a lot of copper wires,
becomes the other polarity of the antenna, is that
what you mean, if so, this may make sense
because also in the Half Wave Dipole Antenna
as seen in Jay's link the two halfs of the antenna
are not physically connecetd.
I think the thing that is confusing me is that in t.v.
vhf antennas both sides of the output come from
the same piece of metal, i.e. they are physically
conneceted, whereas with a Half Wave Dipole
Antenna the two sides are physically isolated,
there is something not intuitive about this.