On Sunday 21 October 2007, Jan Hoevers wrote: > Chuck wrote (in an earlier thread) on 18-10-2007 14:21: > > <snip> > > maybe that's why my offset on the pps kept drifting between > > -5 to +5 microseconds. it seemed to do that about every 4 or 6 > > hours. maybe when it switched to different satellites? > > or are gps geostationary? > > No, gps satellites are not geostationary. > That question was not the core of Chucks post, but since some insight in > the satellites' orbits can save a lot of trial and error when > positioning the antenna, I will take the opportunity to spend a few > words on it. > > The instructions that came with your receiver recommend "clear view of > the sky". Unless you live in the middle of a desert a clear view of the > entire sky will be impossible. Luckily you won't need that, because - no > matter where on earth you live - a large part of the sky will never show > any gps satellites. You can make clever use of this when you have to > position the antenna in a suboptimal position, e.g. on a window. > > The orbital plane of any gps satellite has an angle of 55 degrees with > the equatorial plane, taking the satellite up and down between 55 deg > north and 55 deg south. The satellite constellation populates a band - > more or less donut shaped - around the earth, centered around the > equatorial plane. No gps satellite ever flies over the poles (some other > sats do). > > Seen from the earth' surface that leaves a large circular area of the > sky - centered over the pole - where no sats fly. In tropical and > temperate zones part of that circle is below the horizon, at latitudes > of more than 55 deg the entire circle is above the horizon, and a > (small) part of the "opposite side of the donut" becomes visible at the > northern horizon (southern horizon if you're down under). > > Close to the poles the sats will appear to remain close to the horizon, > with the unpopulated circle overhead, while near the equator two > unpopulated circles are visible, north and south, making the sats appear > in a band from east to west. >
that explains a lot! where the gps will be in its final destination is 43.4 N so he should place it favoring vertial to southern if i understand this correctly. its still not even dawn yet and im on my first coffee so comprehension is a bit slow :) where i am it explains why i had decent satellite pickup with the antenna placed on an upside-down pail on the ground, my best views are clear sky vertical to north. i am at 29.9N. do i have this right? :) > Myself I live at a latidude of 52 deg north, meaning the northern sky > is not interesting (except for a small band of 3 deg through the > zenith). Consequently I have my receiver glued to the outside of a south > looking window. A position on the roof would be possible, but I won't go > through the trouble, because no improvement can be expected. > > Try to imagine where the satellites fly as seen from your position, it > will help in finding the best position for your gps antenna. > > hope this helps a bit, > Jan Hoevers > _______________________________________________ > timekeepers mailing list > [email protected] > https://fortytwo.ch/mailman/cgi-bin/listinfo/timekeepers > -- Chuck "...and the hordes of M$*ft users descended upon me in their anger, and asked 'Why do you not get the viruses or the BlueScreensOfDeath or insecure system troubles and slowness or pay through the nose for an OS as *we* do?!!', and I answered...'I use Linux'. " The Book of John, chapter 1, page 1, and end of book _______________________________________________ timekeepers mailing list [email protected] https://fortytwo.ch/mailman/cgi-bin/listinfo/timekeepers
