[time-nuts] Time Dilation tinkering

Tom Van Baak tvb at LeapSecond.com
Tue Mar 21 04:58:46 EDT 2017


Hi Hugh,

> If I do the math correctly that's about 14ns difference per 24h the 
> clocks are separated by that altitude. [1]

That's correct. For your 1500m elevation gain, the gravitational redshift, the df/f frequency change, will be about 1.6e-13. To be able to measure with any confidence you'll want your clocks to be stable to about 2e-14, at tau 1 or 2 days.

> This got me to wondering if a Rubidium based standard might do the trick 
> - the Efratom SLCR-101s seem readily available for ~USD$200 mark.

There are tricks and technical factors, but the main one is how stable these are at tau 1 day. Buy or borrow a few of them and see if they are mutually stable to the level required. I suspect not. But perhaps other time nuts could comment on how stable their surplus Rb are out to tau 1 day.

There are lots of other details; some to your advantage, some not. But if the surplus Rb can't perform down in the -14's at a day, even in laboratory conditions, then the rest of the discussion doesn't matter.

Yes, the TAPR TICC counter would work well for this experiment. But to be honest, any old nanosecond-level counter is good enough. I say this not to discourage you from a good excuse to buy a TICC, but to encourage you to do the ADEV math to see how clocks and counters and tau can interact in your favor.

/tvb

----- Original Message ----- 
From: "Hugh Blemings" <hugh at blemings.org>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Monday, March 20, 2017 7:38 PM
Subject: [time-nuts] Time Dilation tinkering


> Hi,
> 
> I've been mostly lurking on the list for some time now and follow with 
> interest the many discussions.  Very much at the early stages of my 
> time-nut journey, but enjoying it so far :)
> 
> I'd like to have a go at re-creating the efforts of Tom (and I gather 
> others) in taking a clock up a mountain for a while and seeing if I can 
> measure the relativistic changes.
> 
> Being based in Australia gives me a couple of challenges, for one we 
> don't really do mountains in the same sense as much of the rest of the 
> world - so the highest peak I can readily get to from Melbourne is about 
> 1,600m ASL.  I live at 80m ASL - so a delta of around 1,500m altitude 
> and several hundred km drive.
> 
> If I do the math correctly that's about 14ns difference per 24h the 
> clocks are separated by that altitude. [1]
> 
> We also lack quite the same surplus market here as the US, so purchasing 
> a Caesium based standard is well beyond my means.
> 
> This got me to wondering if a Rubidium based standard might do the trick 
> - the Efratom SLCR-101s seem readily available for ~USD$200 mark.
> 
> Clearly there'd need to be a bunch of extra gubbins [2] added to the 
> 10MHz standard to turn it into an actual clock/counter including battery 
> backup and so forth.  And would need a pair of everything.
> 
> Before I delve too far into the planning, I'd be interested in feedback 
> as to whether this style of Rb standard is likely to be up to the task 
> of being the core of such an endeavour or not ?
> 
> Oh I should add - my plan was to build the systems such that they 
> function as nice standalone time/frequency references once this 
> experiment is concluded :)
> 
> Thanks in advance,
> 
> Kind Regards/73,
> Hugh
> VK3YYZ/AD5RV
> 
> 
> 
> [1] gh/c^2 x 3600 x 24  Where h is 1500, g and c the usual values :)
> 
> [2] I presume at a minimum a counter running at a 5ns or less "tick" fed 
> from a frequency source locked to the 10MHz of the Rb standard.  This 
> counter would need to be latched for reading from an external signal so 
> that it can be compared to the second clock.  Not sure but seems the 
> TAPR TICC might have role here :)
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