On 10/07/2010 07:26 PM, Patrick Yeon wrote: > > I would spec that configuration as being sensitive down to -111dBm, as > that is the input signal power that is equivalent to the noise power > you're seeing (you can spot signals so long as they're slightly higher > than -111dBm). Of course, as you do some processing, or change filter > settings, this will change. It also doesn't mean that you could demod > a signal at -111dBm (you still need some margin of SNR), and if you > were speccing for a customer, you might bump that up a bit to give > yourself some 'wiggle room.' > Well, in this case, there's no "demodulation" required, since this is for a radiometer. My working assumption in situations like this is that you need about 3dB above the inherent noise power of the detector to reliably detect the presence of excess noise at the input, assuming very short integration times on the detector.
Incidentally, I also did some numerical work based on the data sheet for the LTC2284 A/D that's used in the USRP2. The NVSD of the LTC2284 is roughly 25.5nV/root(Hz), which converts to roughly -145dBm/Hz NPSD, or roughly 28.5dB noise figure (which if this were an amplifier, would be absolutely awful!). What that means for what I have in mind is that I only need a little bit of gain ahead of the A/D to achieve the sensitivity levels I need. > That's at least how I see it. Anybody else care to weigh in? > -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
