GNU Radio Notes

• gr_fft_vcc (gr_fft_vcc_fftw): shift parameter swaps two halves of frequency-domain data. Enabled by default, so forward transform ends up having DC in centre of array (like in FFT Sink), which would otherwise be in the first element, and first negative would be in the last element.

• gr_diff_phasor_cc.cc:

out[i] = in[i] * conj(in[i-1]);

• gr_quadrature_demod_cf.cc:

gr_complex product = in[i] * conj (in[i-1]);
out[i] = d_gain * gr_fast_atan2f(imag(product), real(product));

• Random Source:
  • When Byte, full range (min/max) is 0-255.

• GLFSR Source:
  • Outputs unpacked bytes (1 bit per byte), so need to use Unpacked to Packed to re-assemble bytes.
  • Degree defines length of sequence before repeating as 2^degree-1. Also selects pre-defined polynomial bit-mask of same degree if Mask is 0.
  • Mask is XOR'd with shift register after each time LSBit that is shifted off is 1 (if 0, selects pre-defined polynomal based of Degree).
  • Seed sets initial state of shift register.