As an avid fan of Raspberry Pi, often putting them to use for DSP applications, I just want to say thank you for your hard work keeping gnuradio working and optimized on the platform!
I've seen some great FET preamp circuits available on the internet, a few of which I've tried out. I'll dust one off and see if I can make it work in this application. On Wed, May 8, 2019 at 4:15 AM Albin Stigö <albin.st...@gmail.com> wrote: > Hi Brad, > > Just some random ideas... What you are trying to do is very doable. Ive > seen a lot of people do it for VLF reception... Usually along with some > kind of FET amplifier before the mic... > > The frequency xlating FIR filter doesn't have great performance on the > rbpi at the moment. > The frequency xlating FFT filter would be better in your case. > > I'm working on a patch that will make these blocks 14 times faster on > raspberry pi so that will also improve things... > > > > --Albin > > > > On Wed, May 8, 2019, 06:06 Brad Hein <linuxb...@gmail.com> wrote: > >> >> >> >> 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. >> >> >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> Discuss-gnuradio@gnu.org >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >
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