[time-nuts] wtd: WWVB info
kb8tq at n1k.org
Sun Aug 9 17:02:45 EDT 2015
Maybe a little more on “why demodulate the phase mod?”.
1) The signal to noise of the recovered data stream will be significantly
better with the phase mod data. The NIST paper is correct about that.
That alone makes it a neat thing.
2) The interference rejection of the phase mod approach is better. This
is a bigger deal in some parts of the country than others. Night time MSF rejection
is not easy here in the Northeast ...
3) You need to demodulate (to some degree) the phase mod to implement
a “frequency reference” receiver. All the fine old ones no longer work directly
with the current WWVB signal.
4) There is more information in the phase mod signal than in the AM modulation
data stream. It would be fun / useful to have access to that data.
5) The last crop of precision receivers came out several decades ago. There
are a *lot* of things you could try today that simply did not make (economic) sense
back then. Propagation prediction based on location, season, and time of day would be
pretty high up on that list.
6) A whole lot has happened in the world of amateur SDR that *could* apply to this sort
of receiver. This is at the “cheap and slow” end of the world. That makes applying
a digital radio a whole lot easier than at microwaves.
7) A lot of us grew up with phase comparison (either WWVB or Loran-C) as
a method of calibrating / evaluating frequency standards. It’s a technique that
is know to work. It may not be of interest to the word at large. It is of interest
to a number of people here on the list.
8) You might learn something by building a receiver like this. Can you detect
the phase transitions to X,XXX us or to XX.X ns? who knows. Can you better
catch cycle slips with the help of the phase mod? Again, unknown until the
receiver is up and running.
9) GPSDO’s are an outgrowth of the original WWVB ( or more generaly VLF)
disciplined standards. We (or at least I) now have piles of these GPSDO things
taking up room in the front hall. They are getting pretty cheap. Using some of
what has been learned in that arena (and some of the hardware) to improve a
WWVB approach is a real possibility.
10) Since GPSDO’s are all over the place. You *can* use one as a reference
for a lot of the development of a WWVB device. We don’t all have to move into
Tom’s basement and “borrow” the H-Maser signal in order to get one going.
Bottom line it’s a “basement compatible” project. It’s not massively expensive. It
does not require “nutty” levels of instrumentation. You can go as far as you desire
towards the full list of bells and whistles. Compared to other “Time Nut” grade projects
it’s towards the simple end of the list. (Consider that home built H-Masers, DIY Rb’s,
Ion clocks, and Cs fountains have been suggested in the past). It’s a *lot* of work and
by no means trivial to do. I’d say it’s worth trying.
> On Aug 9, 2015, at 3:54 PM, Donald <donvukovic at gmail.com> wrote:
> On 8/9/2015 12:01 PM, Bob Camp wrote:
> < snip >
> Back to my original comment, These boards and chips are no longer available in the US.
> From the UK I have purchased some older boards and they do work as described.
> After all the discussion, I guess WWVB is no longer a profitable market.
> Buying boards from far away is all that's left.
> Thanks to all that responded, I just take the easy (and costly) way out.
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