Thanks for the support! Regarding your VLF experiments there's an historically interesting VLF transmitter Grimeton SAQ sometimes active on 17.2kHz. https://alexander.n.se/the-radio-station-saq-grimeton/saq-transmissions/?lang=en
--Albin On Wed, May 8, 2019 at 2:34 PM Brad Hein <linuxb...@gmail.com> wrote: > > 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 _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
