Discussion:
VLF time station, cheap sdrs
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jimlux
2018-12-05 14:55:40 UTC
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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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Dana Whitlow
2018-12-05 20:52:01 UTC
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I generated a spiral plot of phase and amplitude covering about 3 minutes of
WWVB last fall. It's a good-size file, around 2MB as I recall.

Should I send it?

Dana
Post by jimlux
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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Dana Whitlow
2018-12-05 23:04:24 UTC
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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
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
Post by jimlux
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.
_______________________________________________
To unsubscribe, go to
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
Adrian Godwin
2018-12-06 12:25:01 UTC
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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
Post by Dana Whitlow
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
Post by Dana Whitlow
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
Post by Dana Whitlow
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
Post by Dana Whitlow
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"
Post by Dana Whitlow
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
Post by jimlux
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.
_______________________________________________
To unsubscribe, go to
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
_______________________________________________
To unsubscribe, go to
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
_______________________________________________
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To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.

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