Here is an interesting paper on using fiber:
https://pdfs.semanticscholar.org/a37e/04164c01a6bfea2154c8f0dd97f49d1673b0.pdf
I believe it used some of the gear that is(was) used in the GPS
ground stations around the world.
Bob Martin
On 9/1/2018 3:29 AM, Magnus Danielson wrote:
Hi,
It was very telling when I crashed a research group into the reality of
phase/time transfer over fiber compared to frequency transfer. Armed
with a whiteboard and pens, I derived the forumulas and showed how they
worked and not worked. It's a completely different ball-game and their
"known tricks" ain't doing nothing good as it comes to time.
I had to figure much of this out myself as I did nation-wide system
design to achieve the goal. It's a combination of many skills that goes
into designing the full system from scratch and make it fit together.
It's not hard stuff, it's just many details one needs to get right.
Oh the fun.
Cheers,
Magnus
On 08/31/2018 05:15 PM, Bob kb8tq wrote:
Hi
That works fine if you are doing things manual to check a local standard. If
you are trying to
disipline a few thousand cell towers 24 hours a day … not so much. It also
works for
checking frequency. What modern systems need is time. That gets you into a whole
world of resolving and identifying individual edges. The WWVB signal really was
never
set up for this. Loran-C is an example of a signal that was designed to
identify a specific
edge.
Bob
On Aug 31, 2018, at 10:30 AM, Martin VE3OAT <[email protected]> wrote:
But the diurnal phase shifts at VLF are predictable and largely repeatable. Ignore the
phase at night and use only the phase records during the day when an all-daylight
propagation path exists. You might have to "correct" the absolute phase
reading by some multiple of the RF period, but with a low rate of local standard
oscillator drift, this is a simple matter of arithmetic. Back in the day, I managed
Sulzer crystal oscillators at 5 field sites from my office and could maintain phase
continuity for weeks at a time, until we had to diddle the dial on one or several of them
to correct for crystal aging. Then it was just more arithmetic again. Several of the
oscillators had such low drift rates that all I needed was one daily phase reading from
the VLF phase tracking receiver (Tracor 599Js) at those sites to know the frequency of
the Sulzers there.
... Martin VE3OAT
On Thu, 30 Aug 2018 12:27:12 -0400
Bob kb8tq<[email protected]> wrote:
WWVB as transmitted ( = right at the input to the antenna) is a wonderfully
stable signal. As soon as
that signal hits the real world things start to degrade. Propagation between
transmit and receive sites
is a big deal, even at 60 KHz. On top of that, there is a*lot* of manmade
noise at 60 KHz. The receive
signal to noise will never be as good as you might like it to be ?.
I don't know about WWVB, but for DCF77 it's known that sunrise/sunset
causes a phase shift of several 100?s at even moderate distances
(like ~500km). Unfortunately I don't have any measurements at hand.
Attila Kinali
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