[time-nuts] Oops - wrong URL for tvb plot!

Magnus Danielson cfmd at bredband.net
Tue Apr 10 11:47:44 EDT 2007


From: Magnus Danielson <cfmd at bredband.net>
Subject: Re: [time-nuts] Oops - wrong URL for tvb plot!
Date: Tue, 10 Apr 2007 17:28:40 +0200 (CEST)
Message-ID: <20070410.172840.-1382150419.cfmd at bredband.net>

> From: "Tom Van Baak" <tvb at LeapSecond.com>
> Subject: Re: [time-nuts] Oops - wrong URL for tvb plot!
> Date: Tue, 10 Apr 2007 07:46:30 -0700
> Message-ID: <008b01c77b7f$06f91a40$c1ac1cac at pc52>
> 
> > >> Tom's (tvb) plot I referred to in a previous message is at
> > >> 
> > >> http://www.leapsecond.com/pages/3gps/gps-adev-mdev.gif
> > >> 
> > >> Sorry for the confusion.
> > > 
> > > Phew, I was kind of worried there for a while. The ADEV plot showed three
> > > straight parallel lines with no tendendency to converge.
> > > 
> > > Interesting to (finally) see MDEV used for this analysis.
> > > 
> > > Cheers,
> > > Magnus
> > 
> > Me too. Using ADEV to look at the three receivers seemed like
> > the obvious thing to do, but then Brooks suggested I look at
> > MDEV instead and I was very surprised, and pleased, to see
> > the result. It much better reflects what we all do with GPS
> > receivers, something Tom Clark first popularized with his VP
> > TAC a decade ago -- which is to time average the sawtooth
> > away [ OK, for the purists: not to average away to zero, but
> > to reduce it somewhat through short-term averaging ].
> > 
> > The other thing about the plot is that it show a nice real world
> > example where using ADEV doesn't convey the right message
> > at all; using MDEV is closer to the truth.
> 
> Indeed. I have long wondered why you guys are not using MDEV or at least ADEV
> and MDEV.
> 
> Did you drift-rate compensate the measures before ADEV/MDEV them?
> That's another real world effect one may need to handle. For GPS receivers
> against a good reference (H/CS) it may not be such a big issue thought. It
> should be interesting to pull the drift rate values out and plot them alongside
> to see when they take over.

Infact, if you send me the raw data I could process them and see what pops up.
I have some code lying around already. Should get into the habit of doing some
cheesy plots (gnuplot maybe).

Cheers,
Magnus




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