Reg Edwards wrote:

"Roy Lewallen" wrote
Reg Edwards wrote:

Ian, Oh yes they do.

Next to each half wavelength of line there is another half
wavelength
of line in which the current is in antiphase with it. And so, in
the
far field, the fields from adjacent half-wavelengths of line
cancel
each other out.
. . .

No, they don't. They cancel only in two directions, directly normal
to
the plane containing the wires. Radiation occurs in all other
directions, because the fields don't add in antiphase. An example of
an
antenna which uses two closely spaced elements carrying equal
out-of-phase currents is the W8JK.

Roy Lewallen, W7EL

=================================

Roy, I've never head of a W8JK. You are confusing the issue.

The problem is concerned with a LONG balanced transmission line and its
terminations which form part of the whole radiating system. And as we
can agree it is incorrect to consider parts of the system in isolation.

To simplify the questions, wthout loss of rigor, it is best to consider
the line itself as being lossless with matched terminations.

I have stated that power radiated from the system is independent of
line length and nobody has disagreed.

Here on the back row, there's always been a hand raised in disagreement
on that point.

No argument that it's very, very small. But exactly zero - definitely
not.

Indeed, a radiating power calculating formula from reputable authors
(of which I was unaware) has confirmed this.

If you mean the Sterba reference, then please re-read it. All the
endorsements of the formula that you quote are peppered with caveats
such as "an approximation" and "providing that operations are confined
to wavelengths other than those within the ultra-short-wave region."

This is for the very good reason that some small amount of transverse
radiation does exist. Transverse radiation in the plane of the line is
small because the vector components of radiation from the two parallel
lines are equal in magnitude and almost exactly opposite in phase - but
never exactly opposite.

I am probably the only person in this discussion who has actually USED
parallel-wire lines "within the ultra-short-wave region". If you can
maintain good balance, the losses due to transverse radiation are
negligibly small for engineering purposes.

But to claim they are exactly zero is a physical absurdity... and I'll
always disagree with those.

(Sorry, I'll have to be out of this discussion again for a while.)

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek