I posted this a couple of weeks ago.
We have a permanent base set up on a job site. Worked fine yesterday. The guys turned it on today, no signal. I had replaced the antenna a few weeks ago, as it had been on the pole for over a year and it somehow got water in it. I took that one into the office, took it apart, dried it out, then it worked. So I took it to the site this morning, and using a different cable, hooked it up, still no GPS. Got out one of my rovers, it wasn't picking up anything. Called support, and while I was talking to them, the base started working. Switched it back to the original base and it worked. But satellites kept going off and on, from 2-5, until it finally started picking up 8-9. I have no idea why.
Since then, I have set up 2 different bases with new antennas and cables and still getting the same thing. Every morning the foreman calls and says "this thang ain't workin' again". Usually by the time I get there, it is working. But the problem is always the same, only receiving 0-3 satellites for 30 minutes to an hour, then it starts picking up 8-10. Have tried bases with and without Glonass, 450 and 900 mhz radios, still does the same. 2 dozers on site with machine control that run off this base are receiving satellites during these times. It's been in the same place for a couple of years now, no problems until recently. There are a couple of cranes in the area, but they are 7-800 ft. and stationary, plus they have been there for a while. Technician is coming Tuesday to try to figure out what the problem is.
Have you tried using any mission planning software (Trimble) to see what your constellation SHOULD look like for your location? It's a free download.
Something else to consider if you havent already. It sounds like you are losing your almanac. It takes about 45 minutes to aquire a new one. Could it be failing batteries are causing a hard reset every night?
> Something else to consider if you havent already. It sounds like you are losing your almanac. It takes about 45 minutes to aquire a new one. Could it be failing batteries are causing a hard reset every night?
It's an almanac problem.
Not all modern receivers have internal batteries since flash memory is so common, but if it does thats a possibility.
I'd contact the dealer/manufacturer and ask them why it's losing the almanac every time you cycle the power. They will know what to do.
Is there something transmitting in the vicinity during the outages. It seems you have eliminated a hardware problem, so either firmware or something external interfering with satellite reception seems to be the likely issues to deal with, assuming of course there are actually satellites visible.
SHG
All the receivers have been running of a 12 volt power supply hooked up in the office trailer. The 2 new ones are an SPS 851 without Glonass and an SPS 852 with Glonass, both have internal batteries. The power supply is shut off at night and the SPS units have to be turned off to keep them from running all night. Any clues there? That's how they told us to run them.
The receivers on the dozers are receiving satellites, don't think that's an issue.
Maybe someone who knows more about Trimble will chime in. Some receivers have a "sleep" mode and "shut down" mode and a "zero power" mode, with each mode doing slightly different things. Your procedure for shutting down might trigger a memory purge, and force the receiver to reacquire an Almanac the next time it's turned on. It's definitely something to bring up with the tech.
Try turning on the 851/852 without the power supply and see if it does the same thing. If everything starts up good, then turn on the power supply.
Take a rover from out in the grrod area and watch the sat screen while you go over to the base to see if you are dropping sat coverage, or it is the powerup on the base.
I think it causes bad multi-path not dropouts, but they didn't install a chain-link fence in the vicinity recently did they? Last summer saw the poor machine control guys get horribly bad corrections, from what I think was a temp chain link fence near their base antenna. I have seen some seriousl bad shots like that, but can't remember if it was multi-path, or dropouts.
It's a classic almanac problem.
It's not a satellite visibility problem. Even only GPS will see more than 0-3 satellites in the first 30 minutes.
It's not a multipath problem.
Temporary solution is to let them run 24/7 until your dealer can help you troubleshoot the almanac problem. They don't draw much power and are built to run that way.
Call the manufacturer tech support or dealer tech support, describe the problem in details and I bet they know what to do.
> All the receivers have been running of a 12 volt power supply hooked up in the office trailer. The 2 new ones are an SPS 851 without Glonass and an SPS 852 with Glonass, both have internal batteries. The power supply is shut off at night and the SPS units have to be turned off to keep them from running all night. Any clues there? That's how they told us to run them.
[sarcasm]are you next to the test site for lightsquared?[/sarcasm]
That thought did cross my mind.
Sounds like you guys are on the right track. But it's odd that it started doing this on a MS750 base that had been there for a couple of years, then continued with 2 different SPS 85x units. I've sent a link to this thread to the tech guy that's coming down Tuesday to check it out.
It sure seems as something is knocking the GPS signal off the air, the fact that your rover, and replacement base units display the same behavior would seem to rule out almost everything else, especially since the dozer rovers aren't having the issue. When you first had the problem you mentioned your rover didn't work either, did you move away from the base location at that time and see if it worked?
Is the rover at or close to the job shack? Maybe something is being used in there that emits EMF, problem goes away when everybody gets out of the shack in the morning and gets out in the dirt?
It could be a firmware glitch too, I have seen a different brand seemingly refuse to track satellites and then start tracking after waiting, only happened with a particular constellation (time of day dependent). Has your problem been ongoing long enough to see a correlation to time of day? The constellation changes by 28 minutes a week or about 2 hours/month, so in a month if this occurs two hours earlier you will know if it is related to the constellation. If it is, then likely a defect in the firmware for that particular constellation.
SHG
Hi Eddy,
Simple reflashing of firmware might solve your problem.
Regards,
Denmark
Did the Tech figure out the problem?
Checked it out, it worked when they turned it on this morning and he couldn't find any problems. About 30 minutes after he left this afternoon the foreman called and said it had stopped again. Showing 0 satellites on the base. Now we're at the "that doesn't make any sense" phase of support.
They are sending another base to try.
Are there any microwave antennas in the area or other transmitters that could be broadcasting on an intermittent basis? On Trimble 4000 SSE & SSI units I've seen the microwave dishes on towers step on my reception until I moved a few degrees off the antenna's path. I've also seen walkie-talkies and certain cell phones cause the satellite count to drop to zero for a few minutes if used too close to the receiver.
Ok, that's NOT an almanac problem.
Almanac helps on start-up, but wouldn't cause this problem.
If it's losing sats mid-day after working fine, that's another problem.
"Stopped again" could mean a lot of things.
Did the power cycle on the receiver?
How quickly did it reacquire sats?
Like others have said, could be local RF interference or could be a flaky receiver.
> Checked it out, it worked when they turned it on this morning and he couldn't find any problems. About 30 minutes after he left this afternoon the foreman called and said it had stopped again. Showing 0 satellites on the base. Now we're at the "that doesn't make any sense" phase of support.
>
> They are sending another base to try.
