At 08:40 AM 7/10/02 -0400, Tom Rauch wrote:
>The REASON we have models is the actual system is too complex to
>consider. While the models are certainly very good in some aspects,
>they always miss some things.
This is certainly true, but there is another good reason, and that is that
the sheer magnitude of the task required to accurately measure a phenomenon
is impractical.
I remember that back in the 60's and 70's VOA used to employ people whose
job involved monitoring VOA transmitters' signals at various locations
around the globe. Expensive, if you're going to compile a large-enough
data set to be more than anecdotal. They adopted VOACAP as their standard
for propagation analysis and transmitter siting in the 80's, presumably
after satisfying themselves that its results were sufficiently consistent
with the empirical data.
I've always wondered, though, how they made their decisions on their big MW
installations, since these would be near or below the threshhold of
accuracy of VOACAP.
One final comment, on the utility to giving NEC model results to two
decimal places. For those of us who are still learning how to use these
programs effectively, it can be useful to have these numbers, even though
we know the experimental accuracy may be in the +/- 1 dB range. For
example, one important source of error in these models is not using enough
segments to get convergence. If I look at Bill's results, and they aren't
the same as mine, then I want to know why, and in the process I can learn
something.
73, Pete N4ZR
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