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Oh, I am so happy someone posted about this topic here. Does anyone know whether I can use a GPSDO with an SDR to have very accurate timestamps of each I/Q sam
by H8crilA 3y ago
Oh, I am so happy someone posted about this topic here.
Does anyone know whether I can use a GPSDO with an SDR to have very accurate timestamps of each I/Q sample? I don't just want the sampling to run at the correct phase, and without drift, I want a timestamp. Could be any SDR, but I'd prefer something reasonably priced (under $1000). Most SDRs will happily take the 10MHz reference clock, but are not be able to ingest or output time.
- johschmitz 3y agoI did this back in the day using a ublox LEA-M8F module for my PhD work following the instructions posted here: http://www.opendigitalradio.org/lea-m8f-gpsdo http://www.opendigitalradio.org/lea-m8f-gpsdo I also experimented with RTK which this module is capable of. Now there's probably a more up to date ublox module available which could provide even better results using multi frequency GNSS etc.
- H8crilA 3y agoThanks. Does the USRP B200 know how to timestamp individual samples? Or I guess just one sample, the rest is easy.
- Cerium 3y agoNow that you mention it, I remember doing this now. Mine was not for SDR, but data acquisition all the same. I had the PPS and 10MHz signals go into an fpga, while the GNSS UART went to the CPU. The FPGA could be programmed with the current time which was then kept up to date internally. As data was acquired the timestamp was married to each sample and passed around one to one.
- H8crilA 3y agoYeah this should work. I was hoping to avoid having to add an FPGA. On the other hand, BladeRF has an FPGA on board, perhaps it can ingest PPS. It will still be quite a bit if work to write for the FPGA, but at least I'll not have to design PCBs, which is way above my skill level.
- Cerium 3y agoI thought about it some more, you might be able to do this entirely with an off the shell SDR. If you have a device that can record multiple bands simultaneously, and preserve timing between them, then you may be able to record both your target band and the GPS band and then use software later to reconstruct the time out of the GPS recording. See: https://www.rtl-sdr.com/rtl-sdr-tutorial-gps-decoding-plotting/ https://www.rtl-sdr.com/rtl-sdr-tutorial-gps-decoding-plotti...
- H8crilA 3y agoThis is a very interesting idea. I think I could use a BladeRF, it has two input channels. I hope the two channels are perfectly synchronized, by glancing at people's projects it seems that they are.
- eqvinox 3y agoIf you want to build something, ITU-T G.703 + G.8271 (both available for free) outline how this works for telco equipment. There's a low-speed serial channel alongside the PPS / 10MHz signals, carrying the actual wallclock time. It's transported over RS422 on a RJ45 connector for PPS + side channel, SMA (or other coaxial connector) for 10MHz reference. Some devices also accept plain NMEA stanzas as input to read the clock from. (I always thought RS422 for the PPS signal is a bit fishy, not sure how jitter-y those transceivers are. That said the hardware I've seen uses >25Mbaud high-speed transceivers [ISL3180, THVD1452], maybe those are fine in that regard.) A modern 5G base station kinda does what you describe. All SDR these days anyway :)
- rfdave 3y agoI believe the GNURadio folks have implemented at least some of this, so it might be worth poking around GNURadio for a bit, Tags are what you're looking for.
- H8crilA 3y agoI obviously need specific hardware for this first. The rest is not a problem. Or at least it's a smaller problem.