Yo Tom! On Wed, 8 Jun 2016 19:26:21 -0700 "Tom Van Baak" <tvb@LeapSecond.com> wrote: > From one NW GPS farm to another... I'm willing to help you debug > yours. Nothing to debug. I know if I move the antenna I can do better, but it does what I need, and it is near the server that needs it. ntpd caculates precision -22 and the jitter is usually less than 0.5 uSec. More than good enough for my purposes. It makes a dandy Stratum 1 chimer. And 16 meters is not good at all. That is 52 feet! Over just two hours. I bet that gets 2x or more worse over 24 hours. If I cared about location accuracy I would throw away that GPS. Any modern GPS should do way better than that. > > A Garmin 18x reports: > > Altitude Err: +/- 264 ft > > Something is terribly wrong with your setup. The Garmin 18x is much, > much better than this. I know because the 18x was one of the GPS > receivers I brought along on a recent mobile clock experiment. Yes, with good antenna placement it can be better, but the 18x also degrades much quicker than newer GPS when the antenna placement is places badly. > in Tucson: http://leapsecond.com/great2016a/2016a-garmin-18x-2.gif what year is yours? Looking at mine, I see it is actually an 18, not an 18x, so a 12 year old design . Worse than the 18x. > With clear sky view, the peak to peak is under +/- 8 m, and the > (1-sigma) standard deviation is 3 m. Even at the hotel lobby, with > obstructed sky view, the (1-sigma) standard deviation stayed under 7 > m. Your 18x number, +/- 264ft (+/- 80 m), is 10x to 25x worse than > this. It doesn't feel right. My antenna is between two 2 story houses at ground level against a tall hill. It is lucky to get much of a signal at all. I know it would work better in aother location, but it needs to be there next to my main servers. > Off-list, can you send me a day of NMEA from your 18x? Not gpsd > output; but the raw serial ascii data from the receiver. I'd like to > get to the bottom of this. We'll all learn something. I can get you pseudo NMEA, the Garmins work much better in binary mode. When they work in binary mode. :-) I'll start to grab that now. I'll have a 12 hour scatter plot in the morning. While you are waiting check out the attached scatter plot. Now THAT is a good $25 GPS! Beats the heck outta any Garmin. CEP(95) of 1.5 meters over 1,000 seconds. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 gem@rellim.com Tel:+1 541 382 8588

I've had that query before too, but in that case it turned out to be that by default some receivers/software report Mean Sea Level and others Height Above Ellipsoid, or both. Angus. On Wed, 8 Jun 2016 20:33:58 +0000, you wrote: > >I have just installed a Thunderbolt here to get our time and frequency equipment all on the same page. >As I was looking at the display on Lady Heather, I was noticing that the GPS altitude seems rather wrong. >We are in Boulder CO, which is nominally 5430' and the antenna is about 20' off the ground. >The display (near overdetermined position) reads 1589.72991 meters or 5216 and change in feet. >Altitude is a big deal around here. :) > >I suppose 214' isn't that outrageous, but it does bring me to a question: > >How accurate is the altitude number really? > >Thanks.

I'm satisfied that it's reasonably accurate now. It is interesting how much elevation can change without really being obvious to a person on the ground. -----Original Message----- From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Michael Perrett Sent: Wednesday, June 8, 2016 5:28 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] GPS altitude somewhat wrong? I just checked Google Earth and the elevation of your office is 5260', only about 24' off of your GPS estimate if that is your location. Michael On Wed, Jun 8, 2016 at 1:33 PM, Van Horn, David < david.vanhorn@backcountryaccess.com> wrote: > > I have just installed a Thunderbolt here to get our time and frequency > equipment all on the same page. > As I was looking at the display on Lady Heather, I was noticing that > the GPS altitude seems rather wrong. > We are in Boulder CO, which is nominally 5430' and the antenna is > about 20' off the ground. > The display (near overdetermined position) reads 1589.72991 meters or > 5216 and change in feet. > Altitude is a big deal around here. :) > > I suppose 214' isn't that outrageous, but it does bring me to a question: > > How accurate is the altitude number really? > > Thanks. > > > -- > David VanHorn > Lead Hardware Engineer > > Backcountry Access, Inc. > 2820 Wilderness Pl, Unit H > Boulder, CO 80301 USA > phone: 303-417-1345 x110 > email: david.vanhorn@backcountryaccess.com<mailto: > david.vanhorn@backcountryaccess.com> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.