From the GPS signal modernization page:
current GPS PRNs normally broadcasting L2C: 01 05 07 12 15 17 24 25 27 29 31
Using Trimble planning software for one week from today at the site I chose it looks like I will get 4 L2C sattelites available for about three hours starting at roughly 11am ET.
I am going to take a pair of R10s, verify that they are set to observe L2C and see if toggling it on/off affects performance. My gut feeling is that it wont make a difference due to not actually being used in the RTK solution. I am thinking a good check would be to do infill at the base to verify the signals purported by the planning software.
Would anyone with Triumph-1s care to try on their end? I am willing to bet Javad does use the signal in his solution. I don't know if you can quickly toggle which signals are used on the Triumph-1s, though, because most would be using SurvCE (and I don't know enough about SurvCE to know if that is an ability at the DC). Does anyone know?
Definitely not a lab test, but I don't survey in a lab. Usually.
To Be A True Experiment You Would Need...
...an antenna signal splitter and use two receivers on a single antenna. Then you would need to set one receiver to record L2C data and one receiver to instead log P2 data, then submit both files to OPUS-RS which uses the P1/C1 and P2/C2 data in solutions. Then study your returned solutions. Since I do not have such receivers I do not know if you even have an option on the recorded observation. That option may only be invoked when creating a RINEX file.
I am unsure of how RSGPS is handling such data and have found that current NGS staff may not be up to full speed with OPUS-RS. Recently I had to be a pest to NGS to get them to find out that OPUS-RS was not using CORS that reported more than 9 observables. Newer receivers may report that they have up to 11 observables, yet only output 6 or 7. My solutions were not using nearby CORS with the extra data positions. After my nudging they found that problem and changed the settings.
A few weeks ago I was looking at some recent data from Alaska that include 5 satellites with L2C observables at the same time. OPUS-RS was not very happy but I have not been able to isolate a problem. It may have been similar to the above problem and I missed it. When they turn on PRN 30 there should be an opportunity to get at least 5 satellites with L2C signals at certain times in the lower 48. There will be 4 L2C satellites in Plane A, 2 in Plane B and 3 in Plane C.
GPS signal splitters are available on the internet for $50-$100. You want to make sure that the signal splitter includes a DC power blocker so that the antenna only gets power from one receiver. If the signal splitter has an internal power blocker there would typically be a small depression with a black dot on the face near that receiver connection. Power blockers are also available separately. You can usually successfully split the signal to 2 receivers without boosting the signal power. I have seen signal splitters for up to 8 receivers, mostly used to test new/repaired receivers from a single outdoor antenna.
Lastly you would have to find out if your manufacturer's post processor uses more than L1 and L2.
Paul in PA
To Be A True Experiment You Would Need...
Actually that is all way more in-depth than I meant. All I was planning to do was to see if the RTK accuracy would change with L2C on or off. Mostly wanted to see if it would fix under canopy better with it on then off...more of gee-whiz approach than anything.
I only mentioned logging infill to make sure I had enough L2C signals during the test to make the test valid.
To Be A True Experiment You Would Need...
The fixed ambiguity solution is ultimately an L1 carrier phase solution; L2C doesn't contribute to the accuracy, it just helps you get there faster. As I understand it, most GPS software uses a wide lane solution to establish the search region for the ambiguities. With the P2 code encrypted, it's difficult to reconstruct the L2 carrier - every manufacturer spent years trying to overcome this, with varying degrees of success. The L2 carrier is necessary to calculate both the wide lane solution and the atmospheric biases that can be differenced out by comparing multiple frequencies. L2C gives the receiver a signal that it can latch onto and use to more effectively demodulate the L2 carrier.
At least, that's more or less how it was explained to me when the R7 and R8 were introduced.
To Be A True Experiment You Would Need...
The only reason I thought of it to begin with was because I emailed Javad info asking about L5 on the Triumph-2. This was the reply:
All JAVAD GNSS multi frequency GNSS receivers are prepared for the potential 2020 sunset of P-code on L2 as they have the ability to track L2C. L2C will more than adequately replace P-code on L2 and it is scheduled to be available on 24 GPS space vehicles by 2018:
When combined with L1 C/A in a dual-frequency receiver, L2C enables ionospheric correction, a technique that boosts accuracy. Civilians with dual-frequency GPS receivers enjoy the same accuracy as the military (or better).
For professional users with existing dual-frequency operations, L2C delivers faster signal acquisition, enhanced reliability, and greater operating range.
L2C broadcasts at a higher effective power than the legacy L1 C/A signal, making it easier to receive under trees and even indoors.
Source: http://www.gps.gov/systems/gps/modernization/civilsignals/
Even now, a JAVAD GNSS receiver will utilize the L2C code in its RTK solution instead of P-code if L2C is present. Using L2C, the precision of our RTK and post processed solutions is a little bit better.
I see what you are saying, though, you still have to have both frequencies.
To Be A True Experiment You Would Need...
I think Javad is blowing a little smoke here... L5 with it's new civilian code will be the standard once enough birds are up. Triple frequency receivers should (according to a white paper one of the Leica guys put out several years ago) also be able to initialize RTK in two or three epochs at 40Km.
To Be A True Experiment You Would Need...
Obviously L5 will be the new standard, but the CNAV broadcast on L2C just came online yesterday. Oddly coincidental with the GLONASS error.
