I worked on a WWVB receiver a few years back. Then realized that I'm in an apparent "null" in the WWVB transmit pattern. Even
my commercial WWVB clocks cannot receive it. Sigh.
on May 15, 2014, Iain Young, G7III <g7...@g7iii.net> wrote:
Hi Everyone,
In recent days I had the idea to plug my LF preamp and antenna into my
192k Soundcard. Even with Nyquist being his usual pain, that still gives
me DC to 96kHz. Perfect for certain time stations :)
I lashed up a linear receiver, put it on 59kHz, and what do I hear ?
"pip pip pip" from MSF. Switch to 76.5kHz, and hear DCF's simpler 100ms
and 200ms "pip pip pip". Thought I'd get adventurous and tried 66.666k,
and I hear pips again (not quite the same, more of this later)
I lashed up a quick Goertzel filter at 250Hz, and re-tuned so I was
250Hz off from MSF. Hacked up some code to actually decode the
output of GRC to the timecode bits for MSF. It decodes perfectly,
even without parity checking!
DCF, I haven't quite got around to that bit yet, but it was detecting
the 100mS and 200mS very well, despite the periodic (relatively) wide
band noise that was around last night.
In case anyone is interested, the flow graphs are located at
http://hal.g7iii.net/GRC/Radio_Clocks/
They are in .grc format, and .png Feel free to use them, however be
aware as well as device changes, you will probably have to fiddle with
the threshold and squelch levels, but they might be a useful starting
point for anyone wanting to do a WWV/WWVB/JJY/BPM decoder.
Now, RBU, There's a thing. It is a little more complex, as rather
than just a carrier, it uses two tones. Only each 100mS is divided,
and there are periods of time with an unmodulated carrier, and even
no carrier at all within each 100mS period.
The gory details are located at
http://en.wikipedia.org/wiki/RBU_%28radio_station%29
This is challenging. The best I have come up with is in the RBU
flowgraphs at the same URL using the CTCSS Squelch block (incl
with a Goertzel filter ahead of it), but I get missing 100mS "packets"
[for want of a better term], and even some times when it thinks both
the 100Hz and 312.5Hz tones are active at the same time! (This is most
likely one squelch not closing before the other opens)
Is this the approach other folks would take with trying to decode
RBU ? Or are there other approaches that might work better ? Suggestions
would be welcomed, and if anyone wants a recording of RBU to test
their own code with, just holler.
Iain
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