Paul: The easiest way to convert a single sample into an I-Q representation is to have a two phase local oscillator. You multiply the incoming signal against the primary phase output of the oscillator for the I channel, and multiply the same sample against the 90 degree offset output for the Q channel.
The quadrature oscillator can be as simple as two sine look-up tables, whose entries are shifted by 90 degrees. The only math is in the sample multiply, and creating the look up tables to start with. If there is a ratio of integers relationship between the sampling rate and the desired local oscillator frequency, then you can get a real clean implementation with reasonably small look-up tables. When running there is no transcendental math involved, just a simple multiply. --- Graham == On Sat, Oct 24, 2020 at 7:37 PM paul swed <paulsw...@gmail.com> wrote: > Antenna and filtering are not a problem for me. I use the 10' X 10' square > loop and about 800' of wire with a cap to resonate at 60 KHz and then a > preamp really to drive 140' of coax. Currently using a modified KD2BD > receiver frontend but using a 350 Hz xtal filter. Yes indeed that hamfest > find was amazing. > > Looks like you have to build a costa loop SDR. Looked at lots of documents. > My first question to the group. > Can a single incoming sample be converted to I & Q through math. I sort of > think so. The original sample might be I and then use math to make Q. That > would save an entire analog chain. The teensy has a single chain for mic > level input. Though it does feed left and right channels. Granted there are > two audio chains at line level. > > The teensy has a NCO that can create a quadrature output. The alternate > would be to use that to drive analog switches as a multiplier to form I & Q > samples. > Regards > Paul > WB8TSL > > > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.