28501 gps

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  • Thanks, Mike. The unit I'm using has a remote antenna, well, remote in the sense that it's on the end of a 6' wire that is attached to a post outside the controller housing. When the unit first wakes it often takes 15-20 minutes to get it's first successful string, but after that it has not been my experience that it takes more than a few seconds to get the data and initiate the position correction for the array. Of course, suspecting that it might be the antenna, I stood out there on a ladder holding it as high as I could looking like an idiot, but that didn't seem to change a thing. It might have changed my neighbors' opinion of me...probably not. Still doesn't mean you're not right.
  • mmoreland wrote: »
    Thanks, Mike. The unit I'm using has a remote antenna, well, remote in the sense that it's on the end of a 6' wire that is attached to a post outside the controller housing. When the unit first wakes it often takes 15-20 minutes to get it's first successful string, but after that it has not been my experience that it takes more than a few seconds to get the data and initiate the position correction for the array. Of course, suspecting that it might be the antenna, I stood out there on a ladder holding it as high as I could looking like an idiot, but that didn't seem to change a thing. It might have changed my neighbors' opinion of me...probably not. Still doesn't mean you're not right.

    Is this an active or passive antenna? If active, does it get the appropriate supply voltage?
    I don't know the type of GPS receiver you are using, but my experience with several receivers is that when the time for the firs fix is very long the antenna or the connecting cable is often the reason. I am used to my receivers get their first fix in about 30-40 seconds from cold start, even when parts of the shy are obscured by buildings.
    --
    Reinhardt
  • I agree with Reinhardt. The cold start (typ) for that chipset/module is 42 seconds. It supposedly has an internal battery backed memory (storing the last almanac, etc?) so I wonder if that battery is inoperative and every restart is now a full almanac, etc., acquisition cycle - which does take 15-20 minutes or so.
    The difference between theory and practice is that, in theory, there is no difference between theory and practice, but in practice, there is.
  • mmorelandmmoreland Posts: 88
    edited 2019-05-21 - 19:47:38
    I'm using a GPS sensor sold by Parallax about six years ago (28501); Digikey number 28501PAR-ND. I haven't saved any records for the remote antenna. Normally the array is activated in less than a minute when it first starts at the beginning of the day, but because there were occasional times when it took a few minutes to begin, the GPS sensor is initiated about 15 minutes before the system that moves the array goes active. For the last six years when I turn it off to wash the array (I turn it off to make it reset to it's most vertical position, so it's easier to wash and squeegee), it resumes searching for and going to its position the minute I turn it back on. The recent difference is that when I turn it back on, the array initializes its position, and then nothing happens until an interval of 4-8 hours passes at which time it begins tracking correctly. This has happened twice in the last month or so.
  • Something changed, for sure. Water intrusion, dirty power/EMI of some sort, other things as commented on and probably much more are all possibilities. Let us know what you find!
    The difference between theory and practice is that, in theory, there is no difference between theory and practice, but in practice, there is.
  • Maybe it's a bad program state. Since the unit is always running no issues. When it starts up it gets in a bad programming state and needs a good nights reset to put it back in state.

    Mike
  • @mmoreland ,

    Don't you have the Epoch time issue on you GPS.
    If I remember the last was in April.
    Look at the date if it is year 2019.

    "GPS week zero started January 6, 1980. The 1024 weeks counter ran out and rolled over on August 21, 1999. The week counter then reset to zero, and it has been recounting ever since. The next time the counter will reach week 1023 and rollover to zero is on April 6, 2019."

    The only solution is firmware update....
  • I've been having the same issue with my PMB-688.

    I hadn't used it for a few years, but a few months ago I started using it again. The first thing I noticed was that even though I'd configured it to 57600 baud, it had reverted to its default 4800 baud. I didn't pay much attention to its initial long time to first sync, as that's understandeable, but what was unusual was it would take up to 20 minutes to sync even after only being shut down overnight. It used to sync really fast.

    Several times I noticed this unexpectedly long time to sync.

    I did a few restart tests, powering it down for 10 to 20 minutes, then starting it, but even after a 20 minute shutdown it did reaquire sync in just a few seconds. I haven't tested it any more extensively than that.

    I don't think it has the GPS weeks issue, because on July 13, 2019, the PMB RMC correctly says "130719":

    $GPRMC,164024.000,A,3755.7998,N,12202.7734,W,0.00,26.85,130719,,,A*42

    whereas on June 24, my old Garmin receiver that has the weeks issue gives a nonsense date "091199" (although everything else works fine):

    $GPRMC,031634,A,3755.7981,N,12202.7766,W,000.0,000.0,091199,015.4,E*6E

    So I guess the PMB-688's internal battery is weak.

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