Re: confusion about path loss calculation for zigbee

Richard Clark wrote:
On Thu, 11 Dec 2008 09:43:05 -0800, Jim Lux <james.p.lux@xxxxxxxxxxxx>
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.
.

Relevant Pages

  • Using A "Combiner" For A SDR
    ... Have 2 scanners working off of a single Scantenna antenna. ... Also have a hardware hf receiver, ... Thinking of getting a new "toy," perhaps a WinRadio SDR receiver. ... each input to the combiner would be fed by a "T" where the ...
    (rec.radio.amateur.antenna)
  • Re: DVD-Recorder mit DVB-T?
    ... Zeit die in's zusammensuchen der Hardware gesteckt haben. ... nicht immer beides programmieren muss (sondern nur den Receiver ... Im Prinzip will man ja vor dem Ueberspielen auf DVD evtl. ... der kann ja auch kurz die Platte ...
    (de.rec.tv.technik)
  • Re: Receiver sensitivity and IF bandwidth??
    ... and therefore its sensitivity, if we simply narrowed the IF's ... bandwidth down from, let's say, 1MHz to 1kHz!! ... Noise figure compares the receiver noise with the noise from a purely ...
    (sci.electronics.design)
  • Re: ADT and SSC speed increase, need help!
    ... The 57,600 bps is the rate at which the hardware transfers data. ... IIgs' serial hardware can handle that speed. ... IIc is a little off of the standard so at higher speeds the receiver ...
    (comp.sys.apple2.programmer)
  • Re: Client/Service relationships & Flow of Requirements.
    ... and it seems as though there is some confusion about various terms. ... the postcondition tells the Sender what the Receiver guarantees ... demanding that the Sender inform it of a particular condition. ...
    (comp.object)