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 <[email protected]> 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 > <[email protected]> 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 >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
