On Sat, 17 Apr 2004 12:22:03 -0700, Roy Lewallen posted this:

Ah, just the person I've been waiting for. How do you account for
current bunching on the conductors (that is, non-uniform distribution of
current around the conductors)? What reference, equation, or program do
you use? Nearly all "first principle" calculations of Q I've seen
grossly overestimate Q, and I believe the failure to take this into
account is at least part of the reason. I haven't seen a decent
analytical method of dealing with it, and an anxious to see how you do it.

Then there's surface corrosion and roughness, radiation, and coupling to
nearby objects. How do you deal with those? Have you identified some of
the other factors that often make a simplistic "first principle"
calculation disagree so badly with carefully made measurements?

Roy Lewallen, W7EL

James Meyer wrote:

If you have to "do the math", you might as well just calculate the Q
from first principles and forget the "measurement".

Jim


I was responding to a suggestion that one could do the math to calculate
what the Q would have been if you hadn't tried to measure it. I was pointing
out that if you could do that math, and get it correct, that you could do the
whole exercise with math and forget measuring anything.

And how do you know for sure that calculations overestimate Q when
measuring Q to verify the calculations disturbs the very thing you're measuring?

An engineer knows when to say "close enough". A mathematician is never
satisfied.

Jim