[time-nuts] WWVB Measurements

Lenny Story lenny at Codematic.com
Sat Mar 26 23:53:42 UTC 2011


Chris,

Regarding the decoding method.

As i stated earlier, i'm using a CMMR-60p, which seems to just be a small
DSP.  If i am remotely successful at my current version, my thoughts are
that i would replace the CMMR with a similar DSP, and just FFT the crap out
of the signal at 60khz... but i have no serious experience at this... so i
could be just talking air here...

-Lenny

On Sat, Mar 26, 2011 at 6:54 PM, Chris Albertson
<albertson.chris at gmail.com>wrote:

> Lenny,
>
> You are ahead of me by many months.  I'm building a WWVB receiver
> also.  Actually I expect I will need to build several before I get
> 24x7 coverage.  My breadboard works only at night in the So.
> California area.   My plan is to place the entire receiver, antenna
> and all on a mast far from the house and use an RS422 serial line to
> send the data back to a computer indoors.
>
> Do you intend to publish your work?   I'd be most interested in how
> you decode the signal.   I'm conflicted between two approaches (1) To
> declare the signal "invalid" if there is any error at all or (2) to
> try and extract as much signal out of the noise as I can.  I may do
> the latter and then have some kind of quality indicator.    The WWV
> audio decoder built into the NTP reference implementation can extract
> time code from what sounds like white noise and static to the human
> ear using sophisticated DSP.  My first receiver will use #1.
>
> About measuring the PPS.If you had a nice HP Universal counter with a
> computer interface that would be best.  You put the PPS from a good
> GPS on one channel and the PPS from WWVB on the other.   Lacking that
> and if you only need to get down to uS level you can use two serial
> orts in a Linux box and use PPS line disciplin on each oert the kernal
> will time stamp the PPS when they happen and software can read and log
> the time stamps. Use the command  "ldattach pps <device>" for each
> serial port.  Good to about 1 uSwhich for WWVB might be enough
>
>
>
> On Sat, Mar 26, 2011 at 1:26 PM, Lenny Story <lenny at codematic.com> wrote:
> > Greetings All,
> >
> > This is my first post to this board.
> >
> > I've completed the first run of a WWVB receiver board and Antenna (custom
> > wound quad). Its an 8051 microcontroller, with a serial port really, but
> it
> > can decode the signal accurately pretty much all day long. (I'm just
> north
> > of boston, MA).
> >
> > I'm wanting to evaluate its performance, my guess is i'll have to produce
> a
> > plot of its PPS. In reading the LeapSecond.com site (awesome btw), the
> > "Allen Deviation" is used.  As this is my first technical, experience in
> > this area, is there a resource or method that is preferred by those who
> know
> > this technology ?
> >
> > The code reports the time delta between each detected second. If i log
> the
> > PPS deltas for an entire day (or week) of detected signal, is that enough
> > data to start figuring out how to do the "Allen Deviation" calculations ?
> >
> > Any resources can you recommend to figuring out the graphs i need to
> produce
> > ?
> >
> > Thanks in advance for your help !
> > -Lenny Story
> > _______________________________________________
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>
>
>
> --
> =====
> Chris Albertson
> Redondo Beach, California
>


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