On 3/11/19 6:27 PM, Hal Murray wrote:
Steve Olney said:
The professional guys were impressed with my data, but slightly disappointed
it didn't have accurate time-stamping. I am working to rectify that for the
next glitch.
>
> What do they need for accuracy?
It depends on your baseline (assuming you're doing interferometry) -
uncertainty in sampling instant turns in to uncertainty in angle.
And then it depends on the integration time (which winds up being the
tau in your ADEV spec, eh?)
>
> Some of the radio astronomy people are world class time nuts. All
the VLBI
> stations have a Hydrogen Maser.
>
> Don't forget the delay through your radio. You can avoid that by
injecting
> the PPS it a spare channel and using that for the low bits of the
time stamp.
> You need something else to number the seconds. Plan B is use the PPS
to keep
> your system clock close to UTC and correct for the delay by measuring
it once
> and assume it doesn't change much.
>
To answer all these sorts of questions (what performance do you need?),
you want Thompson, Moran, and Swenson, "Interferometry and Synthesis in
Radio Astrononmy", 3rd edition
which you can download for free (!) from Springer Open
https://link.springer.com/content/pdf/10.1007%2F978-3-319-44431-4.pdf
https://link.springer.com/book/10.1007/978-3-319-44431-4
This is the book all my radio astronomer colleagues point to.
(I'm building a radio interferometer in space using GPS as the timing
reference to look at the sun - A mission called SunRISE )
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