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

[Patrick Yeon]

On 10/7/2010 2:38 PM, Marcus D. Leech wrote:
> Test setup:
>
>    o A signal generator producing -46dBm at 38.1MHz
>    o USRP2 + Basic_RX
>
>    o GRC flowgraph:
>        o An FFT filter, reducing the incoming 250KHz bandwidth to 5KHz
>        o A power detector:
>
>             (I**2 + Q**2)--->single-pole-iir-filter
>
>        o A strip-chart scope display
>
> Using the scope display, I measured the detector output difference
> between nothing connected (which on the BASIC_RX means that
>    the A/D is "seeing" the 50-ohm termination across the input-half of
> the balun transformer), and my -46dBm signal connected.
>
> That difference amounted to a 65dB difference in detected output power.
> Doing the math, does that mean that a "naked"
>    USRP2 + Basic_RX is sensitive down to roughly -111dBm, or should I
> factor in root(5KHz), which brings it up to -92dBm.

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.'

That's at least how I see it. Anybody else care to weigh in?

--
Patrick Yeon
ThinkRF
613-369-5104 x418