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

[Bob Camp]

Hi

The sawtooth issues of most GPS receivers are much greater than the position errors a short / long survey will produce. Unless you have a very fancy self correcting receiver or a driver that does sawtooth correction, don't' worry about it.

Bob

On May 5, 2013, at 5:33 PM, Tom Knox <actast at hotmail.com> wrote:

> The idea of a Mercury Ion clocks started about 2000 and from about 2005 until recently has held the title of worlds most accurate clock.
> Approx 1 sec per 1.6 billion years the last I heard. At the heart is a single trapped mercury atom. Jim Bergquist at NIST was one of those that lead the development.
> This link has the basics: http://tf.nist.gov/general/pdf/1957.pdf.   I want two.
> 
> Thomas Knox
> 
> 
> 1-303-554-0307
> 
>> Date: Sun, 5 May 2013 06:59:12 -0700
>> From: jimlux at earthlink.net
>> To: time-nuts at febo.com
>> Subject: [time-nuts] vs Hg ion? Re:  GPS clock stabilitiy, Rb vs Cs
>> 
>> 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
>> 
>> <snip>
>> 
>>> 
>>> For rubidium gas-cell, there is a bunch of systematics, including
>> <snip>
>> 
>>> The caesium atomic beam does not have wall-shifts, but rather it has
>>> much lower systematics. One of the major onces being magnetic field.
>> <snip>
>> 
>>> 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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