> At 09:03 AM 7/10/02 -0400, Pete Smith wrote:
> >it can be useful to have these numbers, even though we know the
> >experimental accuracy may be in the 1 dB range.
> For some reason, the reflector strips out the mathematical symbols for
> plus or minus. That's what I meant, "plus or minus 1 dB."
Hi Pete and all,
My point is best illustrated by the A-B comparisons of Rick, N6RK, by
comments from I4JMY, and by my own experiences.
Rick (as I have) has found the losses in verticals not as bad as
predicted in actual tests, and documented what appear to be
discrepancies in ground effects. I'm sure there are probably cases
going the other way.
The problem is, we give exact answers based on models (and
measurements) that are never exact. We often model antennas and
assume they are within a dB or two of the real world, but I'd wager
that is not true in many if not most cases. I'd also bet many of us
even assume they are so perfect even the tenths of a dB count!
I'm sure the models are very accurate if the antenna is far from
earth (in wavelengths) or over a large conducting reflector, and if
nothing goes outside the limits of the model. But in the case of a
simple vertical or an array of verticals near earth (within 1/4 wl or
so of earth) I would expect discrepancies that could sometimes be
significant to making decisions.
Worse yet we have a tendency to compare system hundreds of miles
apart with different equipment, locations, and operators to decide
what antennas "work well" and what antennas "don't work".
I am concerned an over-reliance on computer models that we assume are
"absolute" has collectively given us the impression that we can
predict the real world, and we are as a group losing touch with
understanding how to make valid comparisons between systems.
The same changes are creeping into the ionospheric soup, where we see
silly things like 20-dB coupling loss that can't be measured.
Over reliance on models and under reliance on common sense or a feel
for what is physically happening in a system doesn't exactly push us
towards greater knowledge. A lot of the things we now assume are
concrete numbers are really nothing but best-case trends with many
73, Tom W8JI