On Tue, May 7, 2019 at 4:19 PM Marcus D. Leech <patchvonbr...@gmail.com> wrote:
> On 05/07/2019 04:05 PM, Ben Hilburn 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 > > I should perhaps have entered this discussion earlier, and pointed out one > of my early applications using a sound-card for VLF work: > > https://github.com/patchvonbraun/SIDSuite > > It's OLD now--I don't think it was ever converted to GR 3.7 > > One of the problems with mag-loop antenna is that they're very high Q, and > thus have very small fractional bandwidths, which means that > they're wildly inefficient at all but the resonant frequency. I made up > for that using a Behringer microphone pre-amp using the balanced input. > That meant I could use a fairly "random" multi-turn mag-loop and not > worry about efficiency very much. > > Thanks Marcus - I'll see if I can get it to compile again. In the meantime I have put together an AM receiver flowgraph using recommendations from this thread, along with what I remembered from the gnuradio tutorials and Mike Osman's video tutorials. https://github.com/regulatre/vlfCoilEperiment Given a 5-minute recording, which I included in the repo, I quickly found that QRM interference will be a hurdle and as you pointed out Marcus, my coil (an old VGA degaussing coil) seems to be resonant at undesirable frequencies. In its current installation it's getting overwhelmed by a steady interference source that sounds like ripples coming from a 60Hz half-wave rectifier. There are some gaps in the noise, and as I tuned around within the baseband using my flowgraph (in the repo above), I was able to tune to various parts of the baseband, but in all cases I had too much interference noise. I have a Focusrite Si2 I could use instead, which would have more gain potential and a very low noise floor, but first I think I'll need to find a way to get away from the noise sources.
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