Hi 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.
Bob On Dec 3, 2012, at 2:07 PM, Poul-Henning Kamp <p...@phk.freebsd.dk> wrote: > -------- > In message <AB5B0278225B4BD483382A39E6834203@pc52>, "Tom Van Baak" writes: > >> - 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 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
