Bill,

I was wondering if there was some type of "caulk like" gel inside the antennae cap of the Locus Receiver. Had a small wad of this stuff on the upper part of a receiver today after a session. My first thought was bird poo but when I took a knife edge to it, it was a bit stickier than you would expect for that. A couple of hours later we tried to synchronize this receiver for kinematic work and it would not respond to the handheld. Another receiver was put in it's place and we were able to continue kinematic work for the day. Our dealer is going to send us a loaner until this one gets checked out anyway.
If it's not the receiver, it could be microwave or other intense radio signal that temporarily caused a problem with the IR port. We are working on a project for a client that builds large satellite dishes, transmitting equipment, radar, etc. They may have had something temporarily disturbing our equipment.
Still, the goo stuff bothers me.

Thanks,

J.D. Billings

Bill,

I forgot to mention a very important additional event in the original "question" post. After having the problem with the first unit, I left for the office while the crew continued with kinematic with other two receivers. When I returned to the field, the kinematic work was progressing fine. Just as the crew was taking the last couple of shots I got curious as to how many SV's were recording since we were beginning to get into what should have been a canopy problem area. The rover had shut itself off about 20 minutes earlier, apparantly with no warning. This was in open field conditions. The data stored up until that time downloaded fine. I sent it to Acad to check out the pattern and looked fine. There were three (of about 115) sites that did show as failed vectors. Analysis of these showed them to be in a fairly straight line no more than a couple of hundred feet long. Elevations were obviously out by some 20 feet. Horizontal can't be accurately assessed as these were random shots on grade breaks. Along with the radio or microwave theory (I don't think they were operating at that time but not sure), this "line" of busted sites was perpendicular to the on site transmitting and targeting equipment lines.
I am aware of gps limitations under these type of conditions. Just curious if we have run across a situation on our first real paying gps job where conventional methods must be used instead.

Thanks Again,

J.D. Billings

I have done a couple of surveys around cell towers or microwave radio transmitters where the solutions were a little loose, floating on ambiguities I think. Sessions where the same observations would have produced better solutions.

I did one static shot for 1.5 hours reading 8 satellites to a point 3 miles distant, and got only 1.2 feet accuracy.

I think the radiation is messing up the signal.

Also more kinematics drop out in such locations. I have been recording 6 epochs rather than 4 in such locations and putting the base receiver as far as practicable from the radiation.

These towers often contain several "co-located" transmitters, with all kinds of frequencies being radiated at high energy levels when you are nearby.

J.D.,

No, there is no substance within the Locus receiver that would resemble a caulk-like gel. We have had a very small number of units where a battery has vented causing a small amount of acid to be released into the battery compartment. When dry, the acid resembles caulk powder. If this were the case with your unit, the acid powder would be found in the battery compartment area, not near the antenna cap. Also, the antenna cap is spin welded onto the receiver housing (spun until the plastic melts, welding the two pieces together). Even if the whole receiver was full of gel, it would be hard pressed to find it's way out. My quess would be that this substance came from outside the receiver and that your communication problem was unrelated. Having the receiver services is a good idea. If there is a problem, they will find it.

Regarding whether high power microwave and/or electrical transmission sources can affect GPS operation, I have never been able to get a definitive answer to that question. There are some users who swear that they have experienced difficulties in these environments, other who swear that they have not. Your 3 failed kinematic vectors out of 115 could have been caused by factors other than microwave transmission. i.e. short period of poor PDOP. Or it may have had something to do with the transmissions. In the next release of the processing software, you will be given the tools to more closely look at your data in an effort to determine what may have caused certain vectors to fail. By examining plots of the raw data and processing residuals, you will be able to see exactly how many satellites were available and used, and you should be able to detect if the data is noiser in some parts of the data set compared to others, possibly pointing to interferance problems.

Sorry I could not be more definitive with my response.

Bill Martin
Ashtech Precision Products

By the way, have you received your copy of version 1.2 yet?

Bill,

Yes, we did receive 1.2. It's up and running fine.
Did you see my second post. We're still wondering what caused our second unit (Rover on pole) to shut down without warning. I turned it on in the office and let it run for two hours. Ran fine.

Thanks for the response,

J.D. Billings

J.D.,

Other than a hardware problem, I can think of only two reasons why your receiver would shut itself down:

1. Batteries are low. It's possible that a low set of batteries would still function for 2 hours in the office. Batteries will rebound a bit after being shut off for a while. Also, if the temperature outside was significantly lower than inside, you could get that much run time on a low set of batteries. Was the battery power LED on the receiver yellow or red?

2. As you know, the batteries in the battery compartment are set between springs that maintain the contact. If the pole on which the receiver is placed down hard on a hard surface, it's possible that the batteries moved enough to break the contact resulting in the receiver turning off. It's requires a pretty hard jolt for this to happen though.

Bill Martin
Ashtech Precision Products

Bill

Thanks. As far as the batteries, they only have about 30 hours or so use, if they were in fact new when installed by the dealer. I have no reason to doubt that. The light was green. Used that unit today for a couple of hours with no shut down problem.
After considering your number 2 suggestion, I would have to choose that as the most likely.

Thanks

J.D. Billings

p.s. We used the unit again today that would not respond to the handheld yesterday. It still took a couple of tries to initialize with the handheld today but finally did. We are going to have it checked out.

Thanks Again

J.D. Billings

Have you checked the handheld batteries ? We've had a similar problem because this. Maybe helps.