[time-nuts] The forbidden question

[Michael Wouters]

As promised, here's one pertinent paper, about using cryogenic
sapphire oscillators at mm-wavelengths ( 1 mm = 300 GHz ).
https://arxiv.org/pdf/1106.0021.pdf
It's not the one I was looking for but it's a useful entry point.
One interesting number is that at one mm, the coherence time is
limited to at most tens of seconds because of atmospheric turbulence.
Table 3 is worth a look too.

Cheers
Michael

On Fri, Jun 7, 2019 at 7:17 AM Michael Wouters
<michaeljwouters at gmail.com> wrote:
>
> My radio astronomer colleagues tell me that there is about a 20 minute limit to VLBI observing runs because of atmospheric instability so this limits improvements to be had from better clocks. My recollection is that a maser is still sufficient out to 100 GHz. There is a paper about this that I will dig out later.
>
> Cheers
> Michael
>
> On Thu, 6 Jun 2019 at 12:01 pm, Joseph B. Fitzgerald <jfitzgerald at alum.wpi.edu> wrote:
>>
>>
>> Regarding Dana's remarks on VLBI, consider the recent black hole image released by the Event Horizon Telescope.    Measurements were taken at 230 GHz, and they would like to begin measurements at 345 GHz.    Hydrogen masers were used at each telescope.    I am no expert, but I strongly suspect that a better clock would result in longer/better observations.    The H maser only runs at 1.42 GHz ... the astrophysicist wizards are proposing to do their measurements at about 250 times higher in frequency!
>>
>>
>> -Joe
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