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

[Bob kb8tq]

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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