For educational purposes, I am investigating a carrier recovery scheme for BPSK demodulation. I have synthesized a BPSK modulated signal, assembled a hardware carrier recovery scheme which works well (squaring the modulated signal, bandpass filtering and dividing, aka Costas loop) which I now want to implement as SDR in GNURadio. To do so, I acquire the BPSK modulated signal, extract the carrier by squaring the I/Q data flow and bandpass filtering, all this work fine. Before squaring the signal, I insert a Xlating FIR filter whose NCO frequency will act as the tunable VCO in the hardware version of the carrier tracking circuit.
Question: how can I feedback the output of the lowpass filter (ie error signal of the PLL) to the NCO of the Xlating FIR Filter ? (I have found, following http://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorial_PSK_Demodulation the Costas loop block which works very well with my real signal, but I'd like to implement it manually -- or can't gnuradio-companion close a feedback loop ?) Additional question: since gnuradio-companion 3.7.5 I see a grey "freq" tab in the Xlating FIR filter block, but cannot find any associated documentation or what the use of this input is. Is this the functionality I am looking for ? Thank you, JM -- JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe, 25000 Besancon, France _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
