Re: [Discuss-gnuradio] More sensitivity tests of the USRP2 + Basic_RX

[Marcus D. Leech]

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