On 8/3/2015 5:10 AM, Jeff wrote:

This has been explained previously. A dipole is not balanced when it is
connected to the coax. The shield outer surface presents a third
element which makes the shield side of the dipole different from the
center conductor side. In the case of the resistor the current flowing
in one side must flow out the other, so it is balanced no matter what.
The dipole has no such requirement. If you restrict the current running
into one side and not the other it can do nothing about it.


No, a dipole is still balanced, the coax outer does not create a 3rd
element other than by coupling. If the coax is taken off at right angles
the coupling will be low as similar to both elements of the dipole. The
dipole will never be perfectly balanced but can be a very close
approximation.

Ok, don't call the shield an element.

A balanced antenna does not imply balanced current. The load of the
antenna element on the coax will be equal, but the coax also has a
parallel load from the shield outer surface. The two loads in parallel
result in a different voltage on the end of the coax shield than on the
end of the coax inner conductor. This different voltage causes the
different current flow in the antenna element.

A good illustration showing this can be seen near the top of the web
page linked below.


It your contention about the coax acting as a 3rd element were true then
there would be severe distortion of both the impedance of the dipole and
to it radiation pattern. This is not seen in practice and it is also
demonstrable that there is little current flow on the coax outer when
the dipole is well matched to the coax.

I can't say for myself what happens in practice, but others here and on
the web say there *is* severe distortion in the antenna pattern. See
this link about halfway down the page. This is a EZNEC+ simulation. ymmv

http://www.tomthompson.com/radio/EHa...ommonMode.html

--

Rick