Dear Johnathan, On Fri, Mar 14, 2014 at 2:21 PM, Johnathan Corgan <johnat...@corganlabs.com> wrote: > On 03/13/2014 09:32 PM, Activecat wrote: > >> I try to send square wave from one USRP to another. >> The received signal at the receiver USRP is very different from what >> was being sent. >> This is just a very simple setup. What could be wrong ..? > > What you are seeing is a classic case of frequency/phase offset between > the transmitter and receiver, introducing a "rotation" in the I/Q domain > at baseband equal to the difference frequency. > > In spite of "calibrating" things, you have only made the transmitter and > receiver local oscillator frequencies "close". All real-world receivers > must implement a correction loop to estimate this frequency and > compensate for it, which eliminates the rotation. This correction loop > often takes the form of a phase-locked loop, of which there are several > in GNU Radio. For the type of waveform you are transmitting, the "PLL > Carrier Tracking" loop should work, as your baseband waveform results in > significant carrier energy when upconverted to passband.
I was told that the Ettus SBX daughtercard has built-in PLL capability. In this case is the flowgraph-based PLL still necessary ..? Refer below message from Ettus support engineer. > ---------- Forwarded message ---------- > From: Marcus D. Leech <mle...@ripnet.com> > Date: Sun, Feb 2, 2014 at 8:50 PM > Subject: Re: [Discuss-gnuradio] undocumented SBX behavior > To: Activecat <active...@gmail.com> > >> On 02/02/2014 07:03 AM, Activecat wrote: >> Dear Marcus, >> At the receiver USRP, does the SBX daughtercard have any mechanism of >> phase-lock-loop (PLL) ? >> I guess the daughtercard should have it because PLL is essential for >> quadrature downconversion. >> Please advise, thanks. >> Regards, >> activecat > >Yes, the synthesizers are PLL based. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
