Jim, you are patialy correct but 99% only talk, never build any thing Bert Kehren
Sent from Samsung tabletJim Lux <jim...@earthlink.net> wrote:On 7/6/13 7:23 PM, Bob Camp wrote: > Hi > > Ok, lets *assume* there is some uber secret gizmo in the sat that makes the > unsupervised signal absolutely perfect when transmitted from the sat. > > The sat still moves relative to the ground. It's speed is a vector in three > dimensions (up / down , north / south, east / west). Depending on your > location relative to the sat, the doppler will be different. > > A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll > do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz. > > If doppler is in the 50 to 100 Hz range, you need to cancel it by > 1000:1 > simply to get the carrier as good as a simple GPSDO. That's going to require > accurate position data on the sat, it's velocity (all real time), and your > location. > > ----------------- > > Next you need data on the rest of the constellation. They fly in the same > space as the WAAS birds, and transmit on the same frequencies. As they pass > within the capture area of your antenna you will need a way to figure out > which is the GPS and which is the WAAS sat. > > The easy way to do that would be to run a GPS to get all the data and then > process it….. > > ---------------- > > Dish costs something > Downconverter costs something > Signal processing the received signal costs something > You still need a GPS > You still need a good local OCXO as a flywheel > > It's going to be tough to convince me that's any cheaper than a GPSDO > I think you're right.. But time-nuts don't always go for the "easy" way.. _______________________________________________ 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. _______________________________________________ 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.
