John, I would tend to believe the problem you are having is more receiver related. If your entire satellite display is going red it means you are losing all the SV's at once. While it's true that there are some pretty big holes in the system right now, you shouldn't just lose everything at once.
The problem could be anything from a bad antenna to a receiver problem. Working with GPS receivers for the last 10 years I have seen many cases of the receiver just dumping everything. It usually comes down to an antenna connection problem or a crystal/TCXO problem in the receiver. About 4 years ago we went through several thousand UT+ and GT+ receivers that would come up, track for awhile, and then drop all channels. They would cycle like this every couple of minutes, with the time between drops getting longer as the receiver warmed up. The culprit was poor quality crystals that were experiencing "micro-jumps", meaning that they were shifting back and forth slightly in frequency. This doesn't affect just GPS receivers. Crystals are still somewhat of a black art. During this period of bad UT+'s I went down to an assembly house in North Carolina that was having horrible thru-put problems because of the jumping UT+'s. Once we figured out what was going on the QA manager related that their Motorola cell phone line had been down for several weeks about a year back because of the very same problem. Turned out to be the same supplier too. Moto doesn't buy crystals from this vendor anymore....... Randy ________________________________________________________________________ _____________________________________________________________ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Neon John Sent: Thursday, September 07, 2006 4:33 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Health of GPS constellation questioned On Thu, 7 Sep 2006 13:12:07 +0200 (CEST), "Bart Smit" <[EMAIL PROTECTED]> wrote: > >On Wed, September 6, 2006 5:22, Christopher Hoover said: > >> [ the story seems overblown to me, but still worth sharing. follow >> the last link for some real data. - ch ] > >The last link is interesting indeed. Seems that the problems are more >perceived than real, with the GPS constellation operating well within >spec, but users wanting more. A more basic question. Do these degradations affect ordinary users? The reason I ask is that I have a GPS navigation system on in my truck 24/7 and use it every waking hour (I'm a retired engineer who's living a childhood fantasy - driving a long-haul 18-wheeler :-) Fairly frequently I experience fairly long intervals where the system goes completely dead. The satellite screen is all red - the system knows where the satellites are but no signal is received. This can last for miles. I've relocated the receiver, even stopping and removing the receiver from the truck just in case EMI was the culprit. Then just as quickly, the receiver gets lock and everything is fine. The distance traveled - sometimes 10 miles or more - during an outage is such that ground interference can fairly confidently be eliminated. Almost all my running is on open interstates so ground factors can be eliminated. I've gotten curious enough about this to bring along another receiver but so far nothing has happened to give me an opportunity to check with the second receiver. The system is Street Atlas with the Delorme Earthmate hockey-puck receiver. I've had this system about 4 years and it is only in the last few months that this has started happening. I'd attribute this to something in my receiver except that I recall also having occasional loss of signal on my other receiver, a Magellan Meridian Platinum, which I just attributed to "stuff happens". John --- John De Armond See my website for my current email address http://www.neon-john.com Cleveland, Occupied TN Don't let your schooling interfere with your education-Mark Twain _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
