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 ------------- Lots of things to slog through. I suspect there are other sat signals that are better candidates. Bob On Jul 6, 2013, at 2:23 PM, jmfranke <[email protected]> wrote: > A lot of the changes from "bent pipe" to the new system including C-band > uplink is explained here: > > http://www.insidegnss.com/node/697 > > > While there, downlink the extended PDF version. > > John WA4WDL > > > -------------------------------------------------- > From: "Magnus Danielson" <[email protected]> > Sent: Saturday, July 06, 2013 12:57 PM > To: <[email protected]> > Subject: Re: [time-nuts] Speaking of Costas loops (WAAS) > >> On 07/06/2013 06:29 PM, Joseph Gwinn wrote: >>>>> Code/Carrier Frequency Coherence: The lack of coherence between the >>>>> broadcast carrier phase and the code phase shall be limited. The short >>>>> term (<10sec) fractional frequency difference between the code phase >>>>> rate and the carrier frequency shall be less than 5x10-11 (one sigma). >>>>> Over the long term (<100 sec), the difference between the change in the >>>>> broadcast code phase (convert to carrier cycles) and the change in the >>>>> broadcast carrier phase shall be within one carrier cycle (one sigma). >>>> >>>> >>>> This is interesting. Does it imply that they regenerate the code on board? >>> >>> Very unlikely, because then the bird would have to understand every >>> possible code, including those not invented when the bird was launched. >> >> If it is within the Gold codes being used for GPS and WAAS, they only need >> to alter the 10 bit reset-value of the G2 PRN code. See the WAAS >> specification, as this method is being recommended for receivers. >> >> Within that limit, it is relatively cheap to provide code tunability. >> >> Cheers, >> Magnus >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
