On 05/08/2019 08:33 AM, Brad Hein
I actually used one of these for my VLF work a few years back:
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
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.
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
On Tue, May 7, 2019 at 4:19 PM Marcus D. Leech <address@hidden
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
I should perhaps have entered this discussion
earlier, and pointed out one of my early
applications using a sound-card for VLF work:
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
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.
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
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
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