On Sun, 7 Dec 2008 15:11:33 -0800 (PST), Ginu
wrote:

My current result doesn't
make sense because the power required to transmit at 250 kpbs for
Zigbee is less than the power required to reach the receiver at a
modest 300m away.

This is your first and most significant clue to the failure of
analysis, and it is very "path loss" oriented (the path loss
differences for your two scenarios should be almost infinitesimal).
The disparity in your computations are due to transcription error, or
math error. You should have now been able to put that to rest.

Wouldn't adding to my path loss further deteriorate
my result? I'm trying to wrap my head around this.

This is your confusion factor, and it relates to transcription error
in the abstract: you are using the wrong formulas entirely regardless
of the accuracy or correctness of arithmetic results.

The greater part of discussion has focused on Shannon-Hartley issues
which have their own application to the full mix of your original
problem.

Try unwinding the thread so that you are not trying to force a
solution out of a broken premise. None of this really sounds like
finding the missing decimal point, or the corrupted divisor is going
to solve anything.

If you think this is still path loss related, and you are showing
results in actual implementation (bread-boarded hardware, on the
bench); then you have to open up the discussion beyond the limited
math to include the conventional problems of interference and
multipath.

73's
Richard Clark, KB7QHC