From: Dr Bruce Griffiths <[EMAIL PROTECTED]> Subject: Re: [time-nuts] GPS: ADEV or MDEV? Date: Sun, 15 Apr 2007 01:17:17 +1200 Message-ID: <[EMAIL PROTECTED]>
> Magnus Danielson wrote: > > From: [EMAIL PROTECTED] > > Subject: Re: [time-nuts] GPS: ADEV or MDEV? > > Date: Sat, 14 Apr 2007 14:46:42 +0200 (CEST) > > Message-ID: <[EMAIL PROTECTED]> > > > > > >> On Sat, April 14, 2007 13:32, Magnus Danielson said: > >> > >>> From: Peter Schmelcher <[EMAIL PROTECTED]> > >>> Subject: Re: [time-nuts] GPS: ADEV or MDEV? > >>> Date: Sat, 14 Apr 2007 02:40:57 -0700 > >>> Message-ID: <[EMAIL PROTECTED]> > >>> > >>> > >>>>> Surely its better to detect the pseudorange instability in software (if > >>>>> one has access) rather than attenuating the signal from all SVs. > >>>>> Another option is to use multiple GPS antennae operating as a phased > >>>>> > >>>> array. > >>>> > >>>>> Bruce > >>>>> > >>>> Of course but I think that approach is part of sub nanosecond time > >>>> transfer > >>>> accuracy. Attenuation is simple and the results are descent. The signal > >>>> is > >>>> less than 6dB above the receiver noise floor to acquire SV. > >>>> Unfortunately > >>>> the SV do not have matched output power so they are acquired and > >>>> weighted > >>>> unequally. > >>>> > >>> The difference in path-length and thus space attenuation is compensated by > >>> the > >>> antenna pattern such that it emits stronger to the rimb of its earth view > >>> than > >>> central. That evens out power-shifts due to space attenuation for the > >>> viewer. > >>> Otherwise we would have yeat another problem to deal with. > >>> > >> Do the HP GPSDOs not have a tuneable maskangle? > >> > > > > Maskangle is indeed setable. > > > > Cheers, > > Magnus > > > > _______________________________________________ > > time-nuts mailing list > > [EMAIL PROTECTED] > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > > Magnus Bruce, > But what is really needed, in general, is to be able to vary the mask > angle with azimuth to account for hills and other obstructions that do > not extend all the way around the the site. I already propsed that some time back. It is fairly easy to do on most GPSes, since you can explicitly block certain SVNs from being included and you can map the signal-strength (and other measures of incorrectness, such as pseudorange deviation) as a function of elevation and azimuth. With such a 2D plot you can not only have a contour of the horizon, you can also blank out spots where excessive multipath corrupts the pseudo-ranges. In essence you now have a 2D mask rather than a 0D/pseudo-1D mask model on a 2D spaceview. It is really not that much programming effort and it is really just the exact command set towards various GPS receivers which changes most of the time. If you like me have many receivers of the same antenna, it is really the same decission that goes for all of them, so the main processing is a joint effort for the site rather than per receiver. You can however compare the result between the receivers. Cheers, Magnus _______________________________________________ time-nuts mailing list [EMAIL PROTECTED] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
