RadioBanter - View Single Post

May 19th 06, 07:02 PM posted to rec.radio.amateur.antenna

On 19 May 2006 10:14:30 -0700, wrote:
I would like to hear from someone who has actually measured the
linearity of a simple antenna. I have not done this, so would only be
one guy with an opinion. Plenty of us around.

Hi Glenn,

Then you have a point in that regard. Bench work is rarely offered
here and when it is, we are lucky if it is accompanied with the
particulars of measurement so that it could be assessed or
re-performed. It took very many years between cfa antenna claims, and
legitimate field work by cfa proponents to show that their claims were
unsupported.

By 'simple antenna' I mean an antenna such as a wire dipole without
traps, baluns or other things that could degrade linearity. Since the
linearity of antenna systems in general is in question, the simplest
setup that answers the question would be best.

Well, a BalUn is one of those elements that would be welcome so as to
enforce the simplicity you demand, and so as to not disturb what is
being measured. The BalUn (more properly, a choke) for this purpose
would be for isolating the antenna from the transmission line.

In the absence of measurement, can anyone comment on the modelling
software? Does it assume and model a linear system? If so, do we know
of any substantial nonlinear departures from the modelling software?

The modelers using NEC generally obtain results that conform to
observable phenomenon. The modelers are supposed to be neutral
observers. In other words, the non-linearity shown by the lack of
congruence to the Cosine curve is not a presumption of non-linearity
by the modeler; it is merely reporting an analysis. It may be noted
that this analysis has been supported by a combination of bench work
and theory.

All of this is the long way of saying non-linearity has been
demonstrated, that is has been measured, and that it has been long
explained. There are no surprises here.

73's
Richard Clark, KB7QHC