[time-nuts] clocks for amateur radio and astronomy (was: World's most precise.... wall clock)

[Bruce Griffiths]

Unless something akin to VLBI or pulsar timing is involved millisecond accuracy will usually suffice for amateur astronomy.

Bruce
> On 11 March 2021 at 06:31 Bob kb8tq <kb8tq at n1k.org> wrote:
> 
> 
> Hi
> 
> > On Mar 10, 2021, at 12:17 PM, Attila Kinali <attila at kinali.ch> wrote:
> > 
> > On Wed, 10 Mar 2021 06:39:46 -0800
> > "Charlie" <charlie at drhabekost.com> wrote:
> > 
> >> My question is thus: It seems that procuring a more precise PPS/time output
> >> unit is quite a bit more costly than what I have; even more costly is a unit
> >> that has both more precise PPS/time output,
> > 
> > The question is more whether it is good enough. How accurate
> > do you need your time? How precise does it need to be?
> > If the answer to both questions is smaller than 100ns,
> 
> I suspect that’s a typo. “larger than 100 ns” ( 1 us > 100 ns ….) 
> would seem to be the correct way to look at it. 
> 
> > then you
> > are good with anything you can get your hands on, even the cheapest
> > GPS receiver. If you need better than that, you need to look
> > more closely and calculate each contributor to uncertainty,
> > both random and systematic and see where you can and want to
> > improve (or compromise).
> > 
> > 
> >> and a really stable 10 Mhz
> >> output ( I might add that I am a Ham, where 1 uhz  error is detrimental).
> > 
> > At what time scales you need that 1µHz stability? Is it for
> > a few seconds? Or over a few hours? How accurate does it have
> > to be?
> > And are you sure it is really 1µHz @ 10MHz? Because that's
> > a stability better than 1e-13. Which isn't something most people
> > just have in their lab. You need a an exceptionally good OCXO to
> > reach down there (an OCXO that costs you as much as a car)
> > and even those reach it only over a very limited Ï„ between
> > about 1s and maybe 100s. Beyond a Ï„ of 1000s you have the option
> > of using a HP5065, possibly with Corby's Super-HP6065 modifications.
> > Even GPS takes until somwhere like 100ks to reach down to 1e-13.
> 
> Even crazier if you are talking about your transmit frequency at VHF :) :).
> Welcome to why Hz, uHz, etc normally are replaced with ppm, ppb, and
> the like … That’s been the case in every place I’v ever worked on this stuff. 
> 
> Bob
> 
> > 
> > If you need better than that, either at shorter or longer Ï„,
> > then we are clearly deep in atomic clock territory. Either
> > hydrogen maser. caesium beam standard or cold atomic clock.
> > 
> > 			Attila Kinali
> > -- 
> > The driving force behind research is the question: "Why?"
> > There are things we don't understand and things we always 
> > wonder about. And that's why we do research.
> > 		-- Kobayashi Makoto
> > 
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