tshoppa@gmail.com said:

Does NIST publish the transmitter bandwidth?  I've never seen it, but I haven't done a serious search.

Maybe somebody near enough to get a clean signal could measure it.  What does a spectrogram look like?

--
These are my opinions.  I hate spam.

Some of the KiwiSDR receivers are close enough to get an excellent signal.
Coincidentally I gave this very experiment a try some weeks back; give me a
few days to find the recordings and analysis scripts.  But the bottom line
is that 100 microseconds seems possible.  The antenna bandwidth is some
hundreds of Hz, if I remember right, but the high resolution would come
from tracking a specific point on the amplitude trailing edge (say, the 90%
point).

Another interesting aspect of the WWVB recordings is that the constellation
diagram shows some brief, large phase excursions during amplitude changes.
Phase accuracy is pretty good steady-state, but near the edges it goes kind
of wild.  Transmitter nonlinearity no doubt.  It could be predistorted out
(even adaptively if desired), but it's probably not worth the trouble.

Cheers,
Peter

On 4/7/19 10:37 PM, Peter Monta wrote:

The precision of measurement isn't so much related to only the bandwidth
of the signal as to the combination of bandwidth, integration time, and
SNR.

THe trick is knowing what the "decorrelation time" of the channel is,
because that sets an upper bound on integration time.  And, of course,
the phase noise of the transmitter and receiver.

In any case, extracting microsecond timing from a 1 kHz BW  signal is
straightforward (assuming sufficient SNR, etc.)

As an extreme example, we measure timing of the round trip radio signal
to Jupiter and back with an accuracy of 1E-15 (5 picoseconds). The
signal is very narrow band (<<1 Hz), but we do integrate for 1000
seconds. And we use other means to disambiguate things like "which
cycle" are we on.

Hi

One would assume that there is a fixed relation between the code and the
carrier “as transmitted”. By the time it gets to you. it may not be something nice
like zero degrees, but there will be a (over some period of time) stable relation.

If you can get the code demodulation to the point that you can start looking at
carrier phase, you then have a lot more edges to integrate against. Since the
vast majority of the code bits can be determined ahead of time, you are not looking
for a needle in a haystack. You are looking for at least a pallet full of needles. :)

Can you get to the 10 us range off of the code? It’s certainly worth trying. My guess
is that indeed you can with enough samples.

Once you are looking at carrier phase all is not perfect. Around sunrise and sunset,
you will have a tough time with WWVB. You also have the basic issue that propagation
does swing your local signal by more than a cycle, even at fairly short distances.
Without some sort of propagation “aiding” your GPSDO or time source will be wandering
a bit over each and every day.

The sunrise / sunset part is ….. errr …. predictable as long as you know where you are.
The first order part of the propagation (day vs night) can be roughly estimated. Do you get
two eight hour long “windows” of data each day or is it more?

If your local standard goes into holdover for 8 hours, is that better or worse than tracking
a couple cycles (at 60 KHz) of swing? If you have the sort of OCXO that is commonly used
in a CDMA GPSDO, it should be capable of 10 us for 24 hours. That should put it in the
“couple of us for 8 hours” range. Compared to (many) 10’s of microseconds due to propagation,
that sounds like a good choice.

Bob