[amsat-bb] Re: Arecibo on 432 MHz Moon Bounce (some calculations)
Robert Bruninga
bruninga at usna.edu
Wed Apr 21 15:57:20 PDT 2010
People need to learn engineering significance. Just because a
calculator spits out 9 digits of precision, using them all shows
a lack of understanding. The value is 244 million watts. The
significance of all the other digits is absolutely meaningless!
The original post was about 400 watts and 60dBi gain. Neither
of those numbers has more than 3 significant digits, Throw in
the gain of a dipole over isotropic which is also a round number
of about 2.14 therefore the answer CANNOT HAVE MORE THAN 3
digits of precision or it is WRONG. The answer given implies a
precision that does not exist.
And if you ask me, the 400 Watts is probably only significant to
maybe 2 digits and from their experience with their Power Amp,
I'd say that they only knew their TX power to ONE significant
digit. So I would not even use the number 244. I would say
"about 200 million Watts" because that is all the precision we
can know from the inputs.
When an engineering student gives me such an answer I shoot them
down hard! Numbers convey not only VALUE but PRECISION. And
implying PRECISION where it does not exist is wrong.
Sorry, but everyone else has given their opinion, so I may as
well say mine ;-)
Bob, Wb4aPR
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