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Martin McCormick martin.m at suddenlink.netHere are some real beginner questions that I would like to have a better understanding of concerning SDR in general and the rtl dongles: I understand that the I and Q signals are both 8-bit numbers so each one can have 2^8 possible levels. Is the in-phase value related to the amplitude of the signal such that frequency variations within the pass band don't change it much? Is the Q or Quadrature value something that varies with whether or not the frequency is higher or lower than the center frequency set in to the device? I could imagine that if the Q value responds to changes in frequency that one could get the effect of a discriminator circuit. I bought a couple of the rtl dongles and tried out the rtl-fm program to receive local FM signals and it worked quite well. Finally, what determines the pass-band? It did seem to get smaller if I tried a 12,000 HZ sample rate. I also was surprised at how accurate the frequency is. Other than the fact that I am at the low end of the learning curve, I see all kinds of possibilities. Martin McCormick WB5AGZ