We have built our own Skydel simulator that is paired with an Ettus X310 SDR running Skydel 23.8.0. We wish to perform simulations that are synchronized to the Live-Sky GNSS signals overhead but are unsure about what additional hardware is required. Our Ettus X310 SDR is currently paired with the Ettus 5-Volt Active GPS antenna and the internal GPSDO but looking through the Skydel User Manual it appears as if a GPS Timing Receiver should be added to the system to support this request. Do we only need a GPS timing receiver to synchronize Skydel to the Live-Sky GNSS signals? We are considering the addition of the ublox ZED-F9T module (pictured below). If we used this timing receiver would we only have to feed the Time Pulse 1 output of the timing receiver into the PPS TRIG IN port of the Ettus X310 SDR (also pictured below)?
You would need to connect the Time Pulse 1 output of the timing receiver into the PPS TRIG IN port of the Ettus X310 SDR as you said, as well as connect the ZED-F9T module via a serial connection (USB) to the Skydel simulator.
You would then go to Skydel’s Preferences and connect the timing receiver in the Sync tab:
You should then see your receiver with the correct time in the Start Time tab (note my receiver currently doesn’t have a PVT in the following screenshot):
Thanks for confirming our suspicion, we thought at first that we would need to purchase an OctoClock-G to support this request but instead we will try out the new Ublox timing receiver.
No problem, I just forgot to mention, Skydel expects NMEA data to get the time from the receiver.
The RMC and GGA sentences need to be enabled on the receiver in order for Skydel to get the time.
Any device that can be connected to via a serial port and provides the RMC / GGA NMEA sentences should work as a timing receiver with Skydel.
I setup our newly acquired ublox ZED F9T receiver with our Ettus X310 SDR and I was able to get Skydel to recognize the timing receivers time-aligned Start Time. When clicking start on a simulation with the X300 output selected however I run into the following message:
Are there other settings I need to configure to support this request with Skydel? Our thought was that we could perform time-aligned simulations using this setup as you confirmed above but it looks like we need some way to provide a 10MHz reference clock. Are we going to have to purchase more hardware? I was hoping to confirm our understanding of Skydel’s requirements in advance of our testing that has now begun but we are a little confused about what else is needed here.
When you want to run a simulation which is synchronized with the live sky, you need to provide to the SDR (X310 here) a PPS from a timing receiver locked to the live sky signals. This is to ensure the simulation is aligned on a sub-second level.
You can’t run the X310 with an external PPS using the GPSDO, which is why Skydel is giving you this error.
You will need to:
Connect the PPS output of your timing receiver to the X310’s PPS input
If your receiver provides a 10MHz output, connect it to the 10MHz input of the X310, otherwise you can use another 10MHz source, it shouldn’t have a lot of impact
I am sorry I forgot to mention this extra requirement, it didn’t come to my mind when I wrote my previous answer.
Thanks for the quick response. We are able to modify how the timing outputs are generated on the ublox ZED F9T but I am unsure if we can generate the 10MHz reference output using it. Would you happen to know how the reference output should be configured? Here are the settings we can modify on the timing receiver:
I looked at the data sheet of the Ublox ZED F9T, and it doesn’t provide a 10MHz output.
Do you have access to another source for a 10MHz signal?
I could always make a request to the engineering team to check if it is a real requirement to have an external 10MHz with your scenario, but it would take some time before you would have access to such a change, if it’s even possible. It might be faster for you to acquire a 10MHz source.
That is unfortunate. We have some SDRs around that we could use but we were hoping for an all in one solution. Our use only requires a single X310 SDR that we want time-aligned to the sky so it seems odd that we can’t use the internal GPSDO on our X310. Is there anyway we can time-align our SDR with the sky using the internal GPSDO? If not, what other component would be suggested for our system that will ensure an accurate 1PPS and 10MHz reference input?
From my investigation, there seems to be no restriction from the X310 to use the GPSDO as the clock source with an external PPS. It seems it was a design choice within Skydel, I will request to change this limitation in the next Skydel release to allow you to run your scenario, I can’t say yet though when the next release is expected to be available.
I can notify you when it has been released. In the mean time, if you have a 10MHz source laying around that would probably be the best to unblock your testing. If you don’t have any, you could also buy a CDM5 or Secure Sync to provide that 10MHz clock.
We managed to track down a suitable 10MHz/1PPS source in the meantime so we should hopefully be good to go for our testing. I know internally that UHD allows for the ability to access the RMC and GGA NMEA data streams from the internal SDR GPSDO that Skydel needs to time-align the output so we were confused as to why that wasn’t being done under the hood. The ability to support that system configuration in the future would be great so if that feature is something that may be added then we would definitely use it.
