Really interesting stuff, people! Travelling wave tubes with 50k hour lives. I wonder what sort of cathode material they use? Ovened crystals with 1 e -13 stability at 100 seconds - wow! Thanks for the info........................................................................................................Don C.
<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free. www.avast.com <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Mon, Nov 30, 2020 at 9:55 AM Jeremy Nichols <[email protected]> wrote: > As the RTGs aged, the Voyagers were commanded to shed parts of their load. > Did the RTG voltage drop, was it the current-supplying capability (or both) > and how did that affect the oscillators, if at all? > > Jeremy > N6WFO > > > On Sun, Nov 29, 2020 at 10:11 AM jimlux <[email protected]> wrote: > > > For those interested in a "typical" (hah!) TCXO spec for a space radio, > > generically similar to the Electra UHF radios on and orbiting Mars, it's > > attached. > > > > The excessively precise frequency (49.244..... MHz) is because it > > matched a particular channel assignment for S-band, and the idea was to > > have the PN code (which is about 3 MHz, proportional to the carrier) be > > exactly 16 samples long. > > > > This is in pre "we can trust an NCO/DDS" days. When it takes years to > > build your spacecraft, ordering a crystal with a 24 month lead time to > > get the frequency "just right" isn't considered a problem. Historically, > > the SDST used a VCXO with a crystal at the frequency at 8*f0, where f0 > > is about 9.xx MHz, and multiplies up by 880 to the transmit frequency > > between 8.4-8.45 GHz. > > > > Today, we use 50 or 100 MHz oscillators (Electra uses 24 MHz, but it's > > an older design) and synthesize the carrier with a DDS feeding a PLL. > > For instance, the Iris cube-sat transponder uses a 50 MHz oscillator, > > and that drives a DDS running at 20 MHz, which is multiplied up in an > > integer N PLL to the carrier frequency. > > > > This is because the missions are shorter development time, and we don't > > want to have to know the frequency until after the radios are built (or > > at least, the oscillators are ordered). For Iris, there were 7 of them > > built for the Artemis-1 mission, and the frequencies are all over the > > space science X-band allocation. > > > > The SDST and older used a DRO as the microwave oscillator, and they just > > don't have the tuning range needed to cover 50-100 MHz tuning range (and > > lordy, we tried a bunch of techniques) - not do mention that DROs have > > noticeable microphonics because the physical cavity is part of the > > resonator. > > _______________________________________________ > > 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. > > > -- > Jeremy Nichols > Sent from my iPad 6. > _______________________________________________ > 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.
