[time-nuts] Re: TIC reference clock in 3-cornered hat

[Bob kb8tq]

Hi

A lot depends on just what is being measured. 

If you are looking at three PPS signals, you *might* be running on 
the internal reference for a second. If you are comparing 10 MHz 
signals, the max time is 100 ns. Getting (say) 1 ps accuracy in the 
first means 1x10^-12 / 1 = 1 ppt on your local reference. In the 
second case it’s 1x10^12 / 100 x 10^-9 = 100,000 ( so 10 ppm). 
In the first case the local reference could matter a lot. In the second
case … not so much. 

The most common approach is to run the local references all off of 
a “good” standard and to align the signals so that it’s not a major 
issue in the results. ( so keep your 1 PPS signals close to each other).

Bob

> On Apr 3, 2022, at 5:50 PM, Marek Doršic <marek.dorsic at gmail.com> wrote:
> 
> Hi,
> 
>     3-cornered hat was mentioned several times past days. What reference should be used for time interval counters comparing oscillator pairs?
> Should internal references be used what ever bad they are? A home standard (4th oscillator)? The third oscillator C when comparing pair A-B? ...?
> 
> Thanks,
>    .marek
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