So, if I understand the recent news on Lightsquared (from GPS World Mag.), part of the problem is that more advanced high precision GPSs dipped further into "their" spectrum as part of multipath reduction techniques or to monitor Omnistar, or other reasons? So, is there a way to know which units monitor which freq.? Could older, low-tech, L1 "post-process only" units, be less effected since they wouldn't have the newer high-tech features?
>dipped further into "their" spectrum
That's a misleading way to word it.
The GPS frequencies are published. There's a chart in this link from a recent post.
They have other signal bands between them. The high precision GPS receivers need to compare track the phase of multiple GPS carriers, and need to have all of those carriers affected similarly by the selective filter in the receiver. It is difficult to make the filters more selective, to reject other nearby signal frequencies, without the filter affecting the phase of the carriers differently (especially with temperature changes in the filter) and thereby messing up the comparison between carriers.
If all the signals in nearby frequency bands are weak satellite signals, as the regulations seemed to imply they would be, then this leads to the best-performing and economical design with moderate selectivity for non-GPS signals. If the signals suddenly come from powerful terrestrial transmitters, then you don't have enough rejection from them, and a redesign faces more difficult tradeoffs.
It was that article that got me thinking about this. I can see from there which bands GPS broadcasts on, I want to know what range my units receive on. Comments like what I posted below lead me to believe that GPS manufactures intentionally went past their GPS freq. to monitor Omnistar, or for multipath reduction techniques. Javad, in what is posted below, says they went the furthest outside of the GPS bands, purposely. So I'm asking, is there any way to look or tell what your receivers listen to? Are newer RTK units that use Omnistar or require on-the-fly multipath reduction more susceptible than older L1-only units? FWIW, we have 2 Topcon Hiper Lites w/Glonass, upgraded to unlimited range w/Airlinks, 4 Sokkia Stratus (L1 Only), and still have 3 old Ashtech Locus (L1 only).
I suspect the Hipers would be more affected than the Locus, but that’s just a hunch.
"Receivers having wider RF front-end characteristics, such as those used for scientific and commercial uses requiring high-precision measurements, and some receivers capable of receiving multiple signals from different GNSS systems (e.g., GLONASS) would remain susceptible."
"Logically, many of today’s high-precision GPS receivers have OmniSTAR/Starfire capability built into their antennas and RF front-ends to look into the 1525-1559 Mhz spectrum for the OmniSTAR/Starfire signals. They don’t focus on particular frequencies in that band because the frequencies change periodically as OmniSTAR users can attest. Also, even if you have the OmniSTAR/Starfire capability turned off in your receiver, the antenna is still designed to look into that band so there's no way around it."
"Press release; Javad Ashjaee; May 23, 2011- My friend wrote to me that in a recent LightSquared test a JAVAD GNSS receiver was more susceptible to LightSquared jamming than other manufacturers' receivers.
Of course we are! Any receiver that can effectively defend against multipath and provide a high precision result will be more susceptible against one or another type of such jammers. Also, the receivers that show they are tracking satellites under jammer and are not affected by the interference, in reality the quality of their collected data may be significantly degraded such that their RTK solution will not converge to fixed, or worse, will provide erroneous results.
We have very wide bandwidth and wide AGC to receive every drop of information and get GPS signals with clear edges to mitigate multipath the number one source of error in high precision applications. Multipath is everywhere. As long as the Earth is below the antenna, or other objects near it, there is multipath!"
BTW, that's why I put "their" in quotes. It is misleading, since it wasnt "their" spectrum, and was off limits, during the R&D phase of modern GPS equipment. But that is what Lightsquared is claiming, of course. It's their spectrum and the GPS recievers are encroaching.
This is probably proprietary information for the most part.
Certain AeroAntennas Cover The Full Light Squared Spectrum
AeroAntenna models AT1665-1 and AT1665-11 cover the frequency range fron 1525-1585 MHz. LightSquared has the 1525-1585 range. Those frequencies were originally assigned to IMMARSAT for satellite broadcasting. I take it that was for other broadcast correction services.
OnStar currently broadcasts 850 MHz analog. Soon they will have to go digital but has LightSquared sucked up their choice?
StarFire (John Deere) broadcasts dgps corrections from IMMARSATs as does WAAS(at 1575 MHZ). They are within the LightSquare frequencies. How is that going to work?
Paul in PA