[time-nuts] PTTI 2012, part 2
paulswedb at gmail.com
Tue Dec 4 14:06:57 UTC 2012
OK now that I am setting out to build one. Would the challenge for a
amateur be that the components you build with are basically dirty. Some how
on the copper pipe it would need to be clean and then brazed I might guess.
All of that makes for a dirty element.
To the vacuum. I used to make vaccuum pumps out of old refrigerator motors.
That would be the first stage of pump down. But how do you take it down
below that? Then I speculate you use a ion pump to get rid of the stuff
On Tue, Dec 4, 2012 at 7:37 AM, Bob Camp <lists at rtty.us> wrote:
> I went through a similar process quite a while ago. The dimensions of the
> actual fountain can be quite small. One could make one the size of a shoe
> box and still have it perform quite well.
> On Dec 3, 2012, at 2:07 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> > --------
> > In message <AB5B0278225B4BD483382A39E6834203 at pc52>, "Tom Van Baak"
> >> - USNO rubidium fountains
> >> While many national labs have developed cesium fountains (for
> >> accuracy), USNO has been gradually building rubidium fountain clocks
> >> (for stability) and 4 of them are now fully operational. The ADEV
> >> of these clocks gets well under 1e-16. The paper will have all the
> >> details but the note I made was that with 20 months of data, the
> >> stability was near 5e-17 at tau 4 months. That's 100x better than
> >> a commercial cesium standard; better than all of USNO's other 70
> >> cesium clocks and 15 H-masers combined. Yes, I've added "rubidium
> >> fountain" to my automated eBay searches.
> > I happened to miss a turn (or something...) and stumbled into the
> > building where they keep those fountains when I visited USNO some
> > months ago. WhatI found most remarkable about them were how compact
> > they were, I still expected fountains to be room size, but these
> > were rack-sized.
> > I asked what the material cost would be and if a competent amateur
> > would be able to do something like that, and the clear message was
> > that the single biggest problem was the vacuum for a vessel that
> > size (when you can't use ferromagmnetic materials) and getting
> > the optical bench calibrated. "Apart from that it's just some
> > plumbing"
> >> - Loran/UrsaNav
> >> CW instead of very low duty cycle Loran pulses would improve S/N [...]
> > Actually, it probably will not.
> > The one smart thing about the LORAN signal is S/N, which means that
> > LORAN for timing purposes is incredible insensitive to noise and
> > at the same time, incredible transmitter power economy.
> > The one caveat is that the GRI has to be a good number, preferably
> > a four (or more!) digit prime number.
> > (You need to grok moduls-arithmetic to really appreciate this, but
> > its the magnitude of the prime factors of the product of the GRI
> > and the disturbing CW which counts: The smaller the are, the harder
> > it is to filter the CW-RFI out.)
> > This is why Europe switched to 4-digit GRIs and almost totally solved
> > CW-RFI by doing so, and why the Russian Chayka at GRI 8000 is totally
> > useless near anything resembling a transmitter.
> > --
> > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> > phk at FreeBSD.ORG | TCP/IP since RFC 956
> > FreeBSD committer | BSD since 4.3-tahoe
> > Never attribute to malice what can adequately be explained by
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