From: Dr Bruce Griffiths <[EMAIL PROTECTED]> Subject: Re: [time-nuts] GPS: ADEV or MDEV? Date: Tue, 10 Apr 2007 17:49:03 +1200 Message-ID: <[EMAIL PROTECTED]>
> Poul-Henning Kamp wrote: > > In message <[EMAIL PROTECTED]>, "Brooks Shera" writes: > > > > > >> The impact of time averaging to suppress white phase noise is illustrated > >> by a new plot TVB has created and placed on his website > >> http://www.leapsecond.com/pages/3gps/gps-adev.gif. > >> > >> These revealing plots show that just a few hundred-second time average has > >> largely removed the performance > >> difference between the aged VP and the newer M12+ and has almost entirely > >> removed the benefit of sawtooth correction (CNS-CNS II). These important > >> results are not evident in the usual ADEV plot. > >> > > > > This is simply not true. No averaging period can ever guarantee you > > will not get a constant offset from the sawtooth. You may get rid > > of the noise, but not the bias. > > > > > Poul-Henning > > Not to mention the case of the GPS receiver with a pathologically stable > local oscillator frequency that generates lots of "hanging bridges" and > little sawtooth. > Since software sawtooth correction is virtually free why not do it, when > such data is made available by the GPS receiver? > > Hoping that the local oscillator frequency is sufficiently unstable > isn't good engineering, one should design to accommodate the worst case > possibilities. Ovenize it to control the sawtooth frequency? Temperature controlled oscillator! :-) Should be fairly simple to acheive, really just a FLL. Cheers, Magnus _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
