On 05/08/2019 08:33 AM, Brad Hein 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.
I actually used one of these for my VLF work a few years back:
https://www.amazon.com/Behringer-MIC800-Microphone-Modeling-Preamp/dp/B000KUENNU
On Wed, May 8, 2019 at 4:15 AM Albin Stigö <albin.st...@gmail.com
<mailto: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
<mailto:linuxb...@gmail.com>> wrote:
On Tue, May 7, 2019 at 4:19 PM Marcus D. Leech
<patchvonbr...@gmail.com <mailto: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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