Where is this DC offset compensation implemented?
Matt Ettus wrote: > > > You are probably seeing the DC offset compensation removing your signal > when it looks like DC. > > Matt > > WaveMaker wrote: > >>I took a 256,000 samples per second stream from the USRP and directly >>displayed the I/Q stream to the X/Y display of a (slightly modified) >>oscope.py. >> >>With a -60dBm unmodulated carrier as RF input, and with the receiver tuned >>within 0.1 Hertz of the the carrier, I expected to see a tight constellation >>of samples slowly rotating around the origin at the rate of (Fcarrier - >>Flocal_oscillator). >> >>To my surprise however, when the carrier & receive frequencies are within >>0.1 hz of each other, the displayed constellation of I/Q only lives around >>[x=0, y=Amplitude]. >> >>I've been scratching my head on exactly why this is and have concluded it >>has something to do with the finite length of the Hilbert transformer - we >>don't really have true input phase because the Hilbert transformer is of >>finite length. >> >>Can a Wise One put into concise words what's causing this phenomena? >> >> >>Then, a second, even more baffling observation: Every few seconds, the >>phase of the constellation seems to slip by 180 degrees and the >>constellation jumps to [x=0, y=-1] for a while. It seems to me that this >>phase jump is at the rate at which the constellation SHOULD have slowly >>rotated, i.e. the constellation rotation angle is somehow constrained to >>being only around those two points. In other words, instead of the phasor >>slowly rotating at 0.1Hz, it jumps between [0,1] and [0,-1]. Thinking about >>this duzi, I conclude that this is somehow related the the above insight, >>but as for the phase JUMP, maybe someone with good fundamental insight can >>share it in simple words for a simple man? >> >> >>(PS: my modifications to oscope.py was limited to allowing manual scaling of >>both axis in XY mode, so i'm pretty sure i haven't messed up something >>significant in the xy display that could cause the above phenomena) > > > -- View this message in context: http://www.nabble.com/Carrier-Phasor-Slides-to-Zero-Phase-tf1951297.html#a5377797 Sent from the GnuRadio forum at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
