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

Magnus Danielson cfmd at bredband.net
Tue Apr 10 11:28:40 EDT 2007


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.

Cheers,
Magnus




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