[time-nuts] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs

Jim Lux jimlux at earthlink.net
Sun May 5 09:59:12 EDT 2013

On 5/5/13 1:48 AM, Magnus Danielson wrote:
> On 05/05/2013 10:05 AM, Attila Kinali wrote:
>> On Sat, 4 May 2013 12:36:20 -0700
>> "Tom Van Baak (lab)"<tvb at leapsecond.com>  wrote:
>>> Rule of thumb: quartz is best short term, Rb or H-maser mid-term,
>>> and Cs by far the best long-term.
>> Ah.. so it's a fundamental limitation. And i was looking for something
>> GPS specific.
>> Any references i could read on those limitations? A quick google
>> did not produce any good results.
> There is a handful of references but picking up a book like "Quantum
> Leap" is a good start.
> Quartz is a bit of (syntetic) rock, cut at some angle(s), cleaned,
> mounted in some hermetic sealed chamber with residue dirt, and mounting


> For rubidium gas-cell, there is a bunch of systematics, including

> The caesium atomic beam does not have wall-shifts, but rather it has
> much lower systematics. One of the major onces being magnetic field.

> The above is a summary of things collected from a variety of sources,
> but I think this coarse walk-through of issues gives some insight as to
> what issues pops up where and the milage vary a lot within each group.
> Modern high-performance rubidium gas-cells outperform the early
> caesiums, high-performance crystals outperform several rubidiums.
> The HP5065A is an example of an old clock with really good performance,
> so modern is not everything, and the modern compact telecom rubidiums
> and for that mater CSAC is more space/power oriented than ultimate
> performance of the technology as such.

I wonder where mercury ion fits in the scheme of things, since that's 
where we're spending some money for spacecraft applications right now. 
It's supposed to be orders of magnitude better than Rb.

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