|Subject:||Re: [Discuss-gnuradio] feedback loop for bpsk carrier recovery ?|
|Date:||Thu, 23 Oct 2014 09:50:40 -0400|
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
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