Hi On Jul 3, 2013, at 3:51 PM, jmfra...@cox.net wrote:
> http://www.navipedia.net/index.php/WAAS_Signal_Structure > > Doppler Shift: The Doppler shift, as perceived by a stationary user, on the > signal broadcast by WAAS GEOs is less than 40 meters per second (≈210 Hz at > L1) So unless you can measure and correct for the doppler, you are at a few hundred Hz at 1.5 GHz. 150 Hz would be 0.1 ppm. That's not very accurate. > in the worst case (at the end of life of the GEOs). The Doppler shift is due > to the relative motion of the GEO. > Carrier Frequency Stability: The short term stability of the carrier > frequency (square root of the Allan Variance) at the input of the user´s > receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding > the effects of the ionosphere and Doppler. > Polarization: The broadcast signal is right-handed circularly polarized. The > ellipticity will be no worse than 2 dB for the angular range of ±9.1o from > boresight. > 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). Once you are past 100 seconds, there's essentially no spec. One cycle per 100 sec is a lot, even at 1.5 GHz > Correlation Loss: Correlation loss is defined as the ratio of output powers > from a perfect correlator for two cases: 1) the actual receiver WAAS signal > correlated against a perfect unfiltered PN reference, or 2) a perfect > unfiltered PN signal normalized to the same total power as the WAAS signal in > case 1. The correlation loss resulting from modulation imperfections and > filtering inside the WAAS satellite payload is less than 1 dB. If you are only after the carrier, the code stuff pretty much does not matter. Bob > > John WA4WDL > > ---- Bob Camp <li...@rtty.us> wrote: >> Hi >> >> The pipe in this case is up on one frequency and down on another. The >> conversion oscillator on satellite that's the weak link, no matter how good >> the signal from the ground happens to be. >> >> Bob >> >> On Jul 3, 2013, at 1:48 PM, Attila Kinali <att...@kinali.ch> wrote: >> >>> On Wed, 3 Jul 2013 08:29:02 -0400 >>> Bob Camp <li...@rtty.us> wrote: >>> >>>> There are two batches of GPS / WAAS sats up there: >>>> >>>> 1) The ones with numbers above 100 that are geosync and that only do WAAS >>>> >>>> 2) The ones with numbers <= 32 that do nav. These are not geosync. >>>> >>>> I believe the only ones with corrected / high stab clocks on board are >>>> those in the second group. The stuff in the first group aren't dedicated >>>> sats, just leased transponders on conventional multipurpose geosync birds. >>> >>> I don't know about WAAS, but AFAIK the EGNOS signals are generated on >>> ground using Cs references and retransmitted by the satelites using >>> a "bend pipe". Ie. the signals should be of time-nut quality even without >>> high accuracy frequency standards in the birds themselves. >>> >>> (Sorry, i'm not able to find where i read about that, so no references >>> today) >>> >>> Attila Kinali >>> >>> -- >>> The people on 4chan are like brilliant psychologists >>> who also happen to be insane and gross. >>> -- unknown >>> _______________________________________________ >>> 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. > _______________________________________________ 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.
