Richard Clark wrote:
On Thu, 11 Dec 2008 09:43:05 -0800, Jim Lux
wrote:

To transmit at 250 kbps on a 5 MHz bandwidth channel centered at 2.5
GHz to a receiver say 10 metres away, you only require 5.8009e-010
watts. That's the problem. This is the maximum power required. It is
far less than the -3 dBm quoted.
A question you need to ask is what's the receiver bandwidth. The
information might only be 250 kHz wide, but if the receiver is 5MHz
wide, it's seeing 13dB more noise, and it might not be able to "acquire"
the narrow band signal.


Really Jim,

Do you think the vendor would specify a bit rate capacity and then
fail to supply the needed bandwith?

Sure.. it's the other way around though.. they might have a wideopen
front end or IF (e.g. 5 MHz wide) and be looking for a narrow band
signal in that big band.

Particularly if you have a system that supports multiple rates, and you
want a single hardware design without adjustable bandwidth, your
hardware has to support the widest band.

You're left with two design choices:
1) have a "minimum detectable signal" threshold that corresponds to the
higher noise floor
or
2) Have a narrow(er) band detector (implemented in software or hardware).

the first is cheaper, and can be overcome by marketing


Part of this veil is Omar holds all the cards while revealing nothing
(another trolling technique). Simply consult:
http://focus.ti.com/docs/prod/folders/print/cc2431.html
and take any of the several links to specifications, applications,
block diagrams, schematics; and it becomes painfully obvious that any
confusion that Omar suffers, is that advice already posted in
abundance devolves to rather simpler issues than Nyquist, Shannon,
Hartley, or more exotic sources.


Well, this IS true.

The whole thing is quite well documented, although if one just reads the
ad copy, it is confusing. Worse, if your manager asks why you can't do
the high rate and max distance at the same time, and you have to resort
to "laws of physics" arguments.