[time-nuts] Re: gravity fields affect time keeping?

[Bob Camp]

Hi

One of the most basic issues with manufacturing any accurate standard / clock is that you
need “something better” for your reference. If you manufacture things like active masers
and 5071’s that makes this a significant challenge. For the MHM-2010 you *might* want to 
demonstrate <1x10^-15 sort of ADEV numbers at 10,000 seconds before they ship. 

One way to go for an ADEV target is to run a reference that is 5X better than the device
you are testing. This makes for less math and far fewer hours spent explaining this and 
that to customers. <2x10^-16 at 10,000 sec puts you into the land of experimental standards. 
There aren’t any off the shelf answers. 

If you want to look at the long term spec on the MHM-2010, you are after 2x10^-16 per day
test results. You are off into the parts in 10^-17 world for a reference. Same basic answer,
not much off the shelf 

One answer is an ensemble of devices. You then might hope that performance improves
by sqt(N). That’s why you see people go to rooms full of fancy standards. Common mode
issues (temperature ….) then become a big challenge. Still, that’s the “why?” when you
see that room full of standards. 

It’s a pretty good bet that whatever the comparison was made to, it is in the parts in 10^-16
per day sort of range and it is monitored in a fashion that can back that claim up pretty
well. Can they back up a 1x10^-16 / day number? You’d have to give them a call and ask.

Bob



> On Feb 1, 2023, at 10:08 AM, Tom Van Baak via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Don,
> 
> > There are no mountains in New Hampshire that are equal to the task.
> 
> Well, that depends. In cases like this you must consider exactly what kind of clock(s) are used. The performance of an old 5061A cesium clock may be different than a later model 5061B and both very different from a 5071A, the model still in use by timing laboratories around the world. Plus there's the high-performance option with even better performance, having a noise floor around 5e-15. That's what I tend to use for my relativity experiments.
> 
> In the short video Joe Fitzgerald posted, we see that the team used Mt Sunapee in New Hampshire which is about 2700 ft (0.8 km). True, that's not very tall and the predicted blueshift from sea level is just 9e-14. I can tell you that a 5061 or equivalent vintage cesium clock would not be adequate for that experiment.
> 
> But they didn't use a pair of surplus cesium clocks. The video makes it clear they used a 5071A [1] for the portable clock, and likely they used a H-maser [2] for the base clock (the Einstein doll is sitting on top of a MHM 2010 maser).
> 
> It appears the clock comparison scene was filmed at Microsemi (was Symmetricom, now Microchip), the company that manufacturers the 5071A and the maser. What you see behind the glass is their main clock room [3]. In other words, this was not some cheap backyard experiment from eBay. See also the original discussion about the video on time-nuts [4].
> 
> There's not quite enough information in the video to calculate the error bars, so I'll not stick my neck out too far on that point. But from what I can tell, the results are totally plausible, in spite of the mountain not being very tall. Thus I'm curious what assumptions or calculations you used to reach the opposite conclusion.
> 
> /tvb
> 
> [1] https://www.microchip.com/en-us/products/clock-and-timing/components/atomic-clocks/atomic-system-clocks/cesium-time/5071a
> 
> [2] https://www.microsemi.com/product-directory/active-hydrogen-maser/4123-mhm-2010-active-hydrogen-maser
> 
> [3] National labs and clock companies often have a special clock room, aka "house standard". The one you see in the video has roots (hp 5060 -> hp 5061 -> hp 5071) back this clock room 50 years ago:
> 
> http://www.leapsecond.com/history/Benchmark.htm
> 
> [4] https://febo.com/pipermail/time-nuts_lists.febo.com/2015-November/subject.html#start
> 
> 
> On 1/31/2023 10:09 AM, Donald E. Pauly wrote:
>> The result is worthless.  This is 6x10^-14 which is within the drift of two cesium clocks.  There are no mountains in New Hampshire that are equal to the task.  Mt Rainier in Washington state barely works.
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