Tom Van Baak said: "This note is just a plea not to apply the speed-of-light number or the "nanosecond a foot" rule-of-thumb out of context."
It works reasonably well as a rule of thumb. It's an upper limit but if you wanted to refine it a bit, divide by two. The average value of sin(x) on [0,pi/2] is 2/pi ie about 1/2. This agrees quite well with the results of the post-processing I described earlier. Cheers Michael On Tue, Jun 28, 2016 at 8:49 AM, Tom Van Baak <[email protected]> wrote: >> So to travel 22 meters is about .000,000,073 Seconds. Or 73 nanoSecond. > > Hi Gary, > > I want to echo what Bob just wrote. People get carried away with "a > nanosecond is a foot" and think it applies 100% to GPS timing and position, > or in this case, elevation errors. > > Equating 22 m with 73 ns, or equating 1 foot with 1 ns is only true in the > impossibly rare case of one satellite directly above you. In reality, 1) most > of the time the SV are further down and so the error is reduced by > sin(angle). And, 2) the GPS timing solution is typically based on lots of > satellites, not just one, and so the effects of position error is further > reduced by the ensemble mean. > > An accurate position is desirable. No question about that. This note is just > a plea not to apply the speed-of-light number or the "nanosecond a foot" > rule-of-thumb out of context. > > /tvb > > > ----- Original Message ----- > From: "Gary E. Miller" <[email protected]> > To: "Mark Barettella via time-nuts" <[email protected]> > Sent: Monday, June 27, 2016 12:31 AM > Subject: Re: [time-nuts] Impact of GPS antenna height measurments > > Yo Mark! > > On Sun, 26 Jun 2016 09:02:55 -0400 > Mark Barettella via time-nuts <[email protected]> wrote: > >> I >> estimate my antenna’s actual height at about +5 m high and the gps >> indicates -17 m. > > Others have covered some obvious details. Different ellipsoids, > long term surveying, etc. > >> My question is will this adversely influence the >> accuracy of the gpsdo output? > > Depends on how accurate you need. I'll assume your estimate is perfect, > which is that your GPS is reading off by 22 meters. > > The speed of light is 299,792 kilometers/second. > > > All else being equal, does a constant 73 nanoSec matter to you? > > For comparision, a Trimble RES SMT 360 only promises 15 nanoSec (1 sigma). > > If all you want is a stable frequency from your gpsdo then the offset > is not relevant. > > RGDS > GARY > --------------------------------------------------------------------------- > Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 > [email protected] Tel:+1 541 382 8588 > > >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
