[time-nuts] New WWVB format...

[paul swed]

Might be a bit of a cost. The SDR runs $1495.
Regards
Paul

On Wed, Sep 26, 2012 at 5:36 PM, Dennis Ferguson <
dennis.c.ferguson at gmail.com> wrote:

>
> On 26 Sep, 2012, at 11:19 , Majdi S. Abbas wrote:
>
> > On Wed, Sep 26, 2012 at 10:13:22AM -0700, Tom Van Baak wrote:
> >> My reading of the document(s) is that the new format will in fact allow
> >> WWVB to be used as a frequency standard with even greater precision then
> >> before, though not with unmodified legacy WWVB carrier receivers. My
> hope
> >> is that one of you will produce a clever reference design for such a T&F
> >> receiver make it available to the group. It sounds like a very fun DSP
> >> project; one that we can all learn from. Bonus points for making it an
> >> open-source Arduino shield. Making it work with both DCF77 and WWVB
> would
> >> also be a plus.
> >
> >       DSP would be good, although I also think an microcontroller
> > implementation could be interesting.  Atmel's ARM MCUs look like they'd
> > be good candidates for this sort of thing.  (Pretty fast, enough storage
> > to do interesting things with it, and a fast enough ADC for 60 KHz.)
>
> This is fine, though to make it maximally useful for time and
> frequency purposes I believe the hardware might need to provide a
> way to synchronize the ADC clock to an external reference, and likely
> some way to time-mark the incoming data (e.g. a quick-and-dirty version
> might feed a PPS signal to the second channel of a stereo ADC, if no
> more elegant solution is available).  A control loop to discipline an
> oscillator's output might use that oscillator to clock the ADC and adjust
> the oscillator to zero the ADC's phase alignment with the input signal,
> if that can be made to work.  A system to measure WWVB propagation delays
> and
> signal levels might instead clock the ADC and the time marker with a
> known-accurate frequency and PPS (e.g. a GPSDO).
>
> RFSpace makes commercial LF/MF/HF SDR equipment with almost the right
> inputs
> for this (an external frequency input and a timing trigger).  What I'd like
> is a tiny-budget version of this just for LF stations.
>
> >       I've got a couple of these that I might use as a development
> > platform:
> >
> >       https://www.olimex.com/Products/ARM/Atmel/SAM7-P256/
> >
> >       Has anyone come up with a reasonable algorithm to implement in
> > a microcontroller?  (DSP development kits are a bit more spendy than I'd
> > like to invest in a prototype. :)
>
> I guess the trouble with this is only that the availability of brute force
> can sometimes make it unnecessary to deal with a lot of complexity.  If
> your
> job is to do a convolution of a model of what you know was transmitted
> against the incoming signal to measure the time alignment then using a
> platform where you can store big blocks of data and do Fourier transforms
> with wild abandon can provide really good results without having to spend
> a lot of time thinking about it.  Even quite modest modern PC hardware
> comes
> with a boatload of memory and is exceedingly speedy, and for some purposes
> it can save a lot of time and effort just to make use of that compared to
> trying to do without.
>
> I have a quick-hack DCF77 PM detector which runs on PC hardware and makes
> use
> of one of the above-mentioned RFSpace receivers for the data acquisition.
>  While
> it is now in boxes being moved, when I get it back up I would love to lose
> the
> RFSpace receiver in favor of something much less costly, but would hate
> trying
> to make this work with something less capable than the PC.  Using a
> microcontroller
> like that to do the A/D conversions and send the data collected out (say)
> an
> ethernet port to a PC which does the heavy computational lifting (that's
> what the
> RFSpace receiver does) would appeal to me, but trying to do without the PC
> would
> not.
>
> Dennis Ferguson
>
>
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