[time-nuts] VLF time station, cheap sdrs

[Adrian Godwin]

Jim mentioned the teensy earlier. This led to a couple of interesting links
:

This thread describes using the internal trim adjustment to lock the cpu
clock frequency onto a VLF transmission
https://forum.pjrc.com/threads/35397-Teensy3-1-as-a-precision-Frequency-Standard

Two SDR implementations on teensy 3
https://hackaday.com/2014/04/25/building-a-software-defined-radio-with-a-teensy/
https://forum.pjrc.com/printthread.php?t=40590&pp=25

and, not teensy but another sdr for MSF
https://www.armms.org/media/uploads/s_day_implementation_of_a_software_defined_radio_for_the_60khz_msf_time_signal.pdf

On Wed, Dec 5, 2018 at 11:05 PM Dana Whitlow <k8yumdoober at gmail.com> wrote:

> Here is my capture of a few minutes of WWVB amplitude and phase from last
> fall.
> It's somewhat larger of a file than I had remembered, more like 3.5MB, and
> it has
> lots of fine detail.  So be prepared for it to take half a minute or so
> (maybe more,
> depending) before it starts to plot.
>
> The data was recorded with an SDR-14 SDR, using a DXE broadband loop
> antenna.  I had to wait until the wee hours to get a decent-looking signal
> in
> my high-line-noise area (Kerrville, TX).
>
> The demodulation was done after the capture was complete, in 'C' SW that
> I've written to make this kind of signal analysis fairly easy and regular.
> Basically
> I examine the spectrum of the raw signal using an FFT, and manually pick
> the
> band limits within which I want to work.  Then I shift that band to roughly
> zero-
> center frequency, and take an IFFT to return to time domain.  At this point
> the
> frequency is invariably a bit off, and I have an interactive graphical
> means of
> correcting the frequency error pretty accurately.  Hence, my "Costas loop"
> is
> really a manual process to de-tilt the phase versus time plot.
>
> Normally I quit there, but realized that I needed a better way to plot such
> a
> long record, so I developed a little program to plot the data in spiral
> form to
> an EasyCAD file, to which I manually added explanatory text.
>
> Thanks to TVB for converting my oversize pdf plot to something reasonable.
>
> Enjoy,
>
> Dana
>
>
> On Wed, Dec 5, 2018 at 4:29 PM Dana Whitlow <k8yumdoober at gmail.com> wrote:
>
> > Here is my capture of a few minutes of WWVB amplitude and phase from last
> > fall.
> > It's somewhat larger of a file than I had remembered, more like 3.5MB,
> and
> > it has
> > lots of fine detail.  So be prepared for it to take half a minute or so
> > (maybe more,
> > depending) before it starts to plot.
> >
> > The data was recorded with an SDR-14 SDR, using a DXE broadband loop
> > antenna.  I had to wait until the wee hours to get a decent-looking
> signal
> > in
> > my high-line-noise area (Kerrville, TX).
> >
> > The demodulation was done after the capture was complete, in 'C' SW that
> > I've written to make this kind of signal analysis fairly easy and
> > regular.  Basically
> > I examine the spectrum of the raw signal using an FFT, and manually pick
> > the
> > band limits within which I want to work.  Then I shift that band to
> > roughly zero-
> > center frequency, and take an IFFT to return to time domain.  At this
> > point the
> > frequency is invariably a bit off, and I have an interactive graphical
> > means of
> > correcting the frequency error pretty accurately.  Hence, my "Costas
> loop"
> > is
> > really a manual process to de-tilt the phase versus time plot.
> >
> > Normally I quit there, but realized that I needed a better way to plot
> > such a
> > long record, so I developed a little program to plot the data in spiral
> > form to
> > an EasyCAD file, to which I manually added explanatory text.
> >
> > Enjoy,
> >
> > Dana
> >
> >
> > On Wed, Dec 5, 2018 at 8:56 AM jimlux <jimlux at earthlink.net> wrote:
> >
> >> https://www.rtl-sdr.com/tag/vlf/
> >>
> >> a fair number of examples -
> >>
> >> As I speculated, the 8 bit RTL-SDR has a problem with strong broadcast
> >> band AM, so you need some sort of LPF.
> >>
> >> There are some examples of "amplified whip into sound card into Rpi"
> >> implementations.
> >>
> >> I didn't see anybody actually decoding or measuring the phase though -
> >> lots of waterfall plots showing the existence of a signal.
> >>
> >>
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> >
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