Not sure how to go about figuring this out.
I have a pair of Topcon Hiper Pro receivers, base-rover setup, controlled by SurvCE. I have been using the pair increasingly to set my horizontal and vertical datums for projects. Typically, I set the base on top of the truck, and let it cook a static session while I make measurements using a the rover. Back at the office, I send the static file to NGS for an OPUS solution, and hold this as control for my project.
This morning, like other mornings, I went to a job site, and set up the base, and it wouldn't observe more than 4 or 5 satellites in an open sky condition. At a distance of only 150 feet from the base, the rover would go autonomous (observing, I noted, 14-15 satellites in comparison to the base's 4 or 5). The best shot I could take with the rover, when located close to the base, was a float shot. I made what observations I could, and decided that it was time to move on to total station work. I tried clearing the NVRAM, and resetting RTK, but it didn't seem to improve.
Then after spending 2 hours or so doing total station work, I happened to look at the base, and it was observing something like 13 satellites, and so I re-observed my control points, and rapidly obtained fixed solutions, as I would have expected from the beginning.
The site where I was surveying is located in the same county, but at an elevation of perhaps 700 feet higher than where I typically work. I performed GNSS surveying with this base-rover pair last week, and had no problems. To my knowledge, I haven't made any recent changes with the equipment, software, etc. I understand that it can take time for the almanac and ephemerides to be collected, perhaps 15 minutes? It seemed to me that I had waited this long. But, maybe I hadn't waited long enough?
Any ideas?
Al
I have a pair a legacy e units.
They have some in common with yours...
All reset. Base, and rover.
N
Thanks, Nate.
I've been told that the almanac and ephemerides files can get "out of date" if the receivers are left sitting around for a long while. The thing that puzzles me is that I used these receivers last week, and they worked fine.
Al
Big Al, post: 422983, member: 837 wrote: Any ideas?
Could be you were picking up someone else's base. If it happens again try changing radio frequencies.
Ran into the reverse of this Sunday, base had a sky full and the rover 25' away had 5 to none. Did the 15 second power button reset and go to good when she came back online.
are you working near a military base international border?
We had a similar issue back in the day, turns out they were intermittently scrambling and that was the cause. We were given a time schedule, updated daily.
Start sleeping in?? :sleeping::sleeping:;);)
Fredh, post: 422989, member: 12570 wrote: Ran into the reverse of this Sunday, base had a sky full and the rover 25' away had 5 to none. Did the 15 second power button reset and go to good when she came back online.
You're probably right, Fredh. Are you using Hipers? What is the 15 second reset you refer to? I followed these steps, using the Hiper MINTER interface (clearing the NVRAM):
1. Turn off the receiver
2. Hold down the FN button while turning on the receiver
3. Continue holding down the FN button until the lights are green
4. Continue holding down the FN button until the lights blink orange.
5. Let go of the FN button
6. Wait
Might have been a corrupt ephemeris rather than an old one.
Shawn Billings, post: 423019, member: 6521 wrote: Might have been a corrupt ephemeris rather than an old one.
Thanks, Shawn. Is an old, or corrupt, ephemeris something that corrects itself over time? How can one find out whether the ephemeris in their receiver is valid and up to date? If it takes 15 or more minutes to load the latest ephemeris, and I've been standing there for 15 minutes waiting for it to update, but am not sure, I might nearly double my waiting time (or more) by resetting the receiver....Any tips?
I can't add much. I only mentioned the possibility of a corrupt ephemeris because it may be a one time occurrence.
Thanks. Whatever it is, whether an outdated or corrupt ephemeris, seems to have been fixed by resetting the receiver. I guess the bottom line is that if it behaves in a similar way in the future, resetting the receiver may be the solution.
Big Al, post: 423007, member: 837 wrote: You're probably right, Fredh. Are you using Hipers? What is the 15 second reset you refer to? I followed these steps, using the Hiper MINTER interface (clearing the NVRAM):
1. Turn off the receiver
2. Hold down the FN button while turning on the receiver
3. Continue holding down the FN button until the lights are green
4. Continue holding down the FN button until the lights blink orange.
5. Let go of the FN button
6. Wait
Im running Hyper SRs and yes the NVRAM reset routine is what I was referring to. Same thing used to happen time to time with the Hyper Plus units and the Legacy ones before that.
Resetting the receiver, FORCES it to download a fresh almanac.
Resetting the receiver, is sort of like turning your computer off, and doing a fresh start.
Gets it going again. When I used the Topcon units, resetting it was a once every 2-3 months thing. If it behaved sluggish, or seemed not quite right, it would often fix it.
N
Well, that's it then. Seems like voodoo, but then again, so does GNSS...
For those unfamiliar with the two different receiver models, the methods to clear the NVRAM on different models of Topcon receivers varies. The end result is the same. The HiPer Pro receivers have both a power button and a Record (REC) button so the two button method of clearing the NVRAM is one of the two methods of doing that reset on the receiver.
The HiPer SR has only one button so the method is to simply hold down the power button for a longer period of time. With the HiPer SR, most people are running those with Magnet and you can initaiate the NVRAM clear process from the controller, which i believe is a more reliable method. I have also observed that it takes a HiPer SR longer to reinitialize follow the clearing of the NVRAM .
"""I have a pair of Topcon Hiper Pro receivers, base-rover setup, controlled by SurvCE. I have been using the pair increasingly to set my horizontal and vertical datums for projects. Typically, I set the base on top of the truck, and let it cook a static session while I make measurements using a the rover. Back at the office, I send the static file to NGS for an OPUS solution, and hold this as control for my project."""
Big Al, now you have me thinking about multipath: you keep a base receiver on top of your truck and wonder why you are having problems. Is the antenna fitted with a large choke ring? Maybe use another tripod and get the base out of signal problems and noise. May just improve things.
Hey, Moe, that's a good point. I hadn't considered to what extent that might be a problem. Here's a picture of my setup. The base gets mounted on top of the pressure treated board up on the roof rack, via a 5/8-11 galvanized carriage bolt thread (obviously, not where it's located inside the side compartment). I got the concept for this from Javad advertisements, where they shows (and promote) the base mounted on top of a vehicle. I can imagine that signals might be reflected off the top of the cap and upwards toward the receiver. Not sure what effect this might have. Like most GNSS receivers, signals below a certain degree above horizontal will be rejected (i.e. below 10 degrees), but I'm guessing that this is a function of the elevation of the satellite relative to the observed position, i.e. the receiver will not know the difference between a "straight" and a "reflected" signal originating from the same satellite.
If multipath is likely to be a problem with this setup, can you or other suggest a homemade solution? Thanks.
Al
Like most GNSS receivers, signals below a certain degree above horizontal will be rejected (i.e. below 10 degrees), but I'm guessing that this is a function of the elevation of the satellite relative to the observed position, i.e. the receiver will not know the difference between a "straight" and a "reflected" signal originating from the same satellite. actually, the 'elevation' should be a computation from the ephemeris/almanac. the antenna simply receives the signal without measuring its elevation angle
see if you can get your mitts on a "choke ring antenna". they are big and clumsy, but would mitigate that multipath well 
your mileage may vary, and the newer antennas and receivers filter noise better. would be cool to see a way to use an old castoff choke ring under your existing, truck mounted base antenna. then check,check and re-check to make sure all the parts work properly
I have seen no issues with a truck mounted base. As long as the receiver is above all the metal there is no problem with multipath. Many of the CORS sites around here are on top of buildings.