Anybody got an explanation why I would be tracking GPS Sv's with an Trimble R6 rover, with a good PDOP, elevation mask of 10 degrees, yet no L2 signal coming in. I phoned the VRS base station 30km away and they were having no issues.
It has happened twice in the last month, in the same area ( Gordons Bay, Cape Town, Soth Africa), 1st time clear skies , this time overcast with rain, no electrical activity though.
When looking at the SV plot and list , the signal to noise ration on L1 is good, but no signal to noise ratio on L2.
There is a very old naval training base here, but for basic training only of personnel, no ships or hardware.
I am thinking some sort of signal interfering with the L2 signal or maybe my receiver is dying, but it works fine anywhere else, drove over to Stellenbosch and no problemns.
Regards
Lee
I've been jammed by microwave transmitters at communication sites before, but those usually only affect you in a narrow beam in front of the transmitter. I suppose that someone or something could be transmitting on a freq. near the L2 freq. and you could be getting jammed. Search the forum for "Lightsquared" and you'll see a ton of info about a potential GPS jamming situation here in the US.
maybe that's the piece of equipment that you should be running over instead of the green one...
:beer:
Are surveying in a low spot or a hole? Are there mountains or large structures between you and the base?
The site is at a base of a 400m mountain range, but it is a VRS survey and the base is 30 km away but practically in line of site. The site is flat about 15m above sea level.
Lee
I was going to say a hardware issue, BUT then you say it works elsewhere, so must be something in that environment. I have had a Leica receiver die once, NO L2, L1 worked fine, ended up being a measurement engine board, it did die on a military installation, maybe they zap GPS units on purpose :-S
SHG
Yip I am pretty sure it is something jamming the signal.
I went back today, same thing, went 800m down the road to another control point, no problemn, initialisation in a few seconds, drove back past the site where the problemn is with the receiver out the window watching the SV list of Signal to noise ratio on L2 and as we approached, the signals of L2 started dropping to zero until there was no L2 from all sv's as we past the area and then suddenly L2 started coming back after 200m or so past.
No idea why, there are only a couple of cell towers within a km or two.
Lee
> Yip I am pretty sure it is something jamming the signal.
> No idea why, there are only a couple of cell towers within a km or two.
>
> Lee
Sounds like alien's to me:-O
The antennas that look like a drum or a dish are usually the culprits. The few I've dealt with were on nearby towers within a few hundred feet of my site. I learned to watch for them and instead of choosing my GPS control points on site randomly I would fire up the GPS to verify signal before setting my control. Their beams were only a few feet wide at that distance and relatively easy to avoid.
