kb8tq@n1k.org said: > Ok, 1 Hz at 437.5 MHZ is roughly 2 ppb. That is pretty much “slam dunk” > accuracy with a GPSDO. Much easier to obtain and set up in a school > environment. The key will be orbit estimation for the +/- doppler part of > it. Orbit estimation is not quite a slam dunk sort of thing. The GPSDO > would also give accurate location. Even with good orbit data, the solution > still requires a good location estimate. What is the orbital period? It would be fun to plot the Doppler over time and see if you can get something that looks like a big chunk of an orbit. Ugh. What is the Doppler due to the Earth's rotation? -- These are my opinions. I hate spam.

On 11/17/17 5:16 PM, Hal Murray wrote: > > kb8tq@n1k.org said: >> Ok, 1 Hz at 437.5 MHZ is roughly 2 ppb. That is pretty much “slam dunk” >> accuracy with a GPSDO. Much easier to obtain and set up in a school >> environment. The key will be orbit estimation for the +/- doppler part of >> it. Orbit estimation is not quite a slam dunk sort of thing. The GPSDO >> would also give accurate location. Even with good orbit data, the solution >> still requires a good location estimate. > > What is the orbital period? It would be fun to plot the Doppler over time > and see if you can get something that looks like a big chunk of an orbit. > > Ugh. What is the Doppler due to the Earth's rotation? > not huge.. Earth is 40,000 km circumference (thank you Napoleon and the Cassinis), so at the equator the velocity is on the order of 500 m/s Doppler is about 600 Hz from earth rotation. 1ppm at mid latitudes

Hi, On 11/18/2017 02:16 AM, Hal Murray wrote: > > kb8tq@n1k.org said: >> Ok, 1 Hz at 437.5 MHZ is roughly 2 ppb. That is pretty much “slam dunk” >> accuracy with a GPSDO. Much easier to obtain and set up in a school >> environment. The key will be orbit estimation for the +/- doppler part of >> it. Orbit estimation is not quite a slam dunk sort of thing. The GPSDO >> would also give accurate location. Even with good orbit data, the solution >> still requires a good location estimate. > > What is the orbital period? It would be fun to plot the Doppler over time > and see if you can get something that looks like a big chunk of an orbit. > > Ugh. What is the Doppler due to the Earth's rotation? You need to compensate for your position, because it would lower due to longitude naturally. Yeah, and then the moon isn't in perfect circular orbit either. The sat is also in a not so perfect orbit, so it would also needed to be measured and characterized. Fun problem. I realized that my on the fly least square algorithms would be nice to adapt to this problem. Cheers, Magnus

Hi > On Nov 18, 2017, at 5:38 AM, Magnus Danielson <magnus@rubidium.dyndns.org> wrote: > > Hi, > > On 11/18/2017 02:16 AM, Hal Murray wrote: >> kb8tq@n1k.org said: >>> Ok, 1 Hz at 437.5 MHZ is roughly 2 ppb. That is pretty much “slam dunkâ€� >>> accuracy with a GPSDO. Much easier to obtain and set up in a school >>> environment. The key will be orbit estimation for the +/- doppler part of >>> it. Orbit estimation is not quite a slam dunk sort of thing. The GPSDO >>> would also give accurate location. Even with good orbit data, the solution >>> still requires a good location estimate. >> What is the orbital period? It would be fun to plot the Doppler over time >> and see if you can get something that looks like a big chunk of an orbit. >> Ugh. What is the Doppler due to the Earth's rotation? > > You need to compensate for your position, because it would lower due to longitude naturally. > > Yeah, and then the moon isn't in perfect circular orbit either. Effectively you have multiple things spinning around in various ways. The “orbit” isn’t a single thing in this case. Earth gravity “lumps and bumps” impact GPS orbits. There are a lot of things to have lumps and bumps in this caae. Depending on the orbit relative to this and that, you may have a fairly limited observation time on each pass. This and that accumulate on the “dark” part of the orbit, but you can’t observe it as it happens. You simply see a jump (versus prediction) at the start of the next pass. Bob > > The sat is also in a not so perfect orbit, so it would also needed to be measured and characterized. > > Fun problem. > > I realized that my on the fly least square algorithms would be nice to adapt to this problem. > > Cheers, > Magnus > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.