On 11/28/20 2:28 PM, Steve Allen wrote:
On Sun 2020-11-29T11:06:18+1300 donald collie hath writ:
Can any group member describe the onboard frequency reference[s] used in
the Voyager space probes? They have done extremely well over the decades -
are they Cesium?, Rubidium?, Quartz?
The ultra stable oscillators USOs are crystals
http://adsabs.harvard.edu/full/2004ESASP.544..131A
One of them has failed, and they were never always on, in which case
the aux osc are other crystals
https://descanso.jpl.nasa.gov/DPSummary/Descanso4--Voyager_new.pdf
--
I don't know about Voyager, but on the SDST and later, the auxosc is a
TCXO with fair to middling performance. A good part of the "art" of
communicating with an "old" spacecraft is knowing/predicting/guessing
where the "best lock frequency" is, because DSN sweeps very slowly
through that frequency hoping the spacexraft receiver acquires it in a
<10Hz BW filter. If you don't see the transmitter frequency (in
turnaround mode) jump when acquisition occurs, you widen up the sweep,
or slow it down, or turn up the exciter power. When round trip time is
measured in hours, this is a slow process<grin>
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