Yes I am very eager and hankful for the suggestions. Trying to make time to build out the flow graph and give it a go. Hopefully tonight!
[Sent from mobile device] On Tue, May 7, 2019, 4:06 PM Ben Hilburn <bhilb...@gnuradio.org wrote: > Hey Brad - just checking in! This is an interesting experiment, and I > would love to hear how it went! > > Big thanks to Kevin and JMF for providing very helpful guidance, here, too > =) > > Cheers, > Ben > > On Thu, May 2, 2019 at 7:12 PM Kevin Reid <kpr...@switchb.org> wrote: > >> On Thu, May 2, 2019 at 1:22 PM Brad Hein <linuxb...@gmail.com> wrote: >> >>> I took a Raspberry Pi and attached a 48KHz USB sound card, with a big >>> magnetic loop antenna fed into the mic. A little cheesy? yes! But I'd like >>> to try and see if I can receive VLF. It's in a remote location with little >>> to no interference so I'm thinking my chances should be good. The challenge >>> I'm facing is that I need to write the SDR logic to "tune" throughout the >>> 0-24KHz tuning range. >>> >>> My question is, being that a sound card source presents samples in float >>> and not the usual complex data type, can I still apply the same SDR logic >>> that we use for SSB/FM/AM demodulation such as those presented in the >>> Gnuradio tutorials (eg. >>> http://www.csun.edu/~skatz/katzpage/sdr_project/sdr/grc_tutorial3.pdf) >>> and if not, how do I go about translating the float input into something I >>> can use to feed existing AM/FM/SSB demodulator flowgraphs? >>> >> >> The first thing you need to do is a "float to complex" operation (which >> will leave the imaginary/Q part zero). If you were to plot the spectrum of >> the resulting you would see that it is symmetric around 0 Hz, containing an >> extra copy of all the signals you're receiving, but that is no worse than a >> more typical received spectrum where the other half contains unrelated >> signals. >> >> After that, the approach is exactly the same as any other receiver >> flowgraph that supports receiving at an offset from the hardware >> center/zero frequency. You can use either the "Frequency Xlating FIR >> Filter" block (which combines a frequency shift and a low pass filter) or >> the "Rotator" block (which performs a frequency shift and would usually be >> followed by a separate filter), and the frequency shift of that block >> should be under user control for "tuning". Then you have a baseband signal >> that you can demodulate. >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >
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