Re: [Discuss-gnuradio] lowest power of the signal that LFRX can receive

[Marcus D. Leech]

On 16/03/2011 1:37 AM, Yan Nie wrote:
> On 03/15/11, Alexandru Csete<address@hidden>  wrote:
> > On Wed, Mar 16, 2011 at 1:07 AM, Marcus D. Leech<address@hidden>  wrote:
> > > > Dear all,
> > > >
> > > > What is the lowest power of the signal that LFRX can receive?
> > > >
> > > > Really appreciate any of your help
> > > >
> > > > Yan
> > > The LFRX has almost no gain, so you're limited by the noise floor of the
> > > ADC.  In the USRP2, you can probably reliably detect
> > >   signals down to about -60dBm or so.  In the USRP1, you need somewhat more
> > > signal, about -50dBm or so.  But those are
> > >   ballpark numbers.  But it depends on the details, and what kind of signals
> > > you're trying to detect, and whether you want to
> > >   demodulate them, or merely detect their presence, etc.
> > Using a signal generator I could measure the "CW sensitivity" down to
> > about -90 dBm. Using a 2 kHz filter this produced a tone clear enough
> > for me to decode morse code. With a tuned vertical antenna ~10 meters
> > long, I get very good reception of AM broadcasting and ham radio
> > traffic around 7 MHz. I was using USRP1.
> >
> > Alex
> Really appreciate your reply. The signal that is trying to be detected is 
> -117dBm, which turns out a larger amplifier is need in my case.
>
> I have another question really need your help: how to corresponds the amplitude 
> set by program to the Vp-p of the front end output of LFTX? Also the same 
> question with receiver side, how to corresponds the amplitude to the received 
> signal Vp-p. The amplitude at transmitter side is set by the program and at 
> receiver side the amplitude is the one of the signal after DDC.
>
> Really appreciate your help
>
> Yan
The only way to do this is to measure and calibrate.  The 
USRP+Daughtercard family aren't precision measurement instruments.  
There's significant variability in the analog components.  So, the only 
way to do is to use already-calibrated measurement tools, and construct 
your own calibration tables.