B210 IQ Recording / Playback, GNU Radio.

[O-I812]

Hello! First, thank you for this amazing program! I have had a lot of fun experimenting with PR above 2 GHz!

I was wondering if it is possible to playback either two recorded IQ files or an interleaved file that has been recorded previously using GNU Radio. The files would be clocked together either as a float or a int16 data type. This would be for post processing instead of live processing.

I see there is an ability to use the space bar to record IQ data (not sure if it is interleaved data) and play it back, I was just wondering if the above is possible?

Thank you for your time and consideration.

[30hours]

Yes the space bar records an interleaved IQ file. You'll be able to replay an IQ file of 2-channel interleaved IQ data. I haven't tested this functionality in a while.

I had a quick look and it appears the replay function for the USRP device has not been implemented.
github.com/30hours/blah2/blob/main/src/capture/usrp/Usrp.cpp

The replay function should work fine using a RspDuo device. If interested I could implement the Usrp replay (or feel free to put in a PR).

Very interested in seeing the results from a satellite radio illuminator if you are comfortable sharing.

[O-I812]

Thank you for getting back to me! Yes, I run the docker image, and I attempted to record and playback the IQ data, but the command line hung, and so I decided to reach out for help.

I do have a RspDuo, however it doesn't seem to go up to the frequency range that I need for my experiment unless I use RF mixers, which I have done, but the conversion loss and noise figure with extra amplifiers makes the detection a little weaker.

Yes, using your software, I had a lot of success with detecting airplanes using a geosynchronous satellite and the emitter and reference, I will post what I learned next. Your software worked great and was amazing, it really got me interested in passive radar! I was just looking to do some data collects overnight, but I also like sleep! ;)

[O-I812]

For my experiment, I used the XM satellite radio down link. The high power down links are the DARS (Digital Audio Radio Service). I found the attached data on FM-6, one of the satellites, and I assume that the follow on (XM-9, XM-10) are similar in power. Have a look at page 15, the S-band down links are +71.0 dBW, this makes sense if you look further and see how many amplifier and the dish size is, its massive. It also makes sense because the car antennas that pick up the service are only 3.7 dBi in gain, so the satellite makes all the power.

890641.pdf

[O-I812]

To the best of my understanding, it is okay to use this satellite for experimentation. Here is what the law states: https://www.ecfr.gov/current/title-22/chapter-I/subchapter-M/part-121

"(xxvii) Bi-static/multi-static radar that exploits greater than 125 kHz bandwidth and is lower than 2 GHz center frequency to passively detect or track using radio frequency (RF) transmissions (e.g., commercial radio, television stations);"

Which this works out well for since the down links are at 2.3 GHz and above.

[O-I812]

So I looked into the signals that are LHCP coming from the satellite and Signal Wiki pointed in the right direction: https://www.sigidwiki.com/wiki/SiriusXM_Satellite_Radio

There are two satellites (Rock & Roll are their names) over the USA, which transmit 2 MHz and 4.5 MHz wide wave forms. I happen to have a linear grid dish (~0.7m) and a LHCP 12-turn helix, so I took a look, and the pictures are the downlinks that I saw (from my B210, 40 MHz/sps.

[O-I812]

[O-I812]

[O-I812]

I have actually performed the passive RADAR experiment using your software and it worked quite well. I was able to detect small airplanes from 2 km to 5 km away using a high gain sector panel antenna for the surveillance channel.

With the help of many others before me, I made a GNU radio glowgraph using the multiply conjugate function with FFT's to get the range, but I couldn't figure out how to do the doppler without a range/doppler plot. So, your software was a huge help!

[O-I812]

I believe that I can use GNU Radio to create a recording and interleaved file. The file can be saved as a float 32 like what comes directly from the USRP, or I can convert the scale to int16 to save on file size.

This is just an example that is found on the internet:

[O-I812]

passive-radar_airport_airplane_south.mp4

[O-I812]

passive-radar_airport_north_cars.mp4

[O-I812]

passive-radar_airport_plane_airplane_south.mp4

[O-I812]

passive-radar_airport_plane_airplane-2322290_south.mp4

[O-I812]

Because of the doppler at the higher frequency, the movement is more pronounced, which is neat. I do have more examples, but I feel like I am spamming you already, let me know if you want to see more.

Anyhow, any help on playing back an interleaved file would be appreciated if you have time time and are interested. The B210 goes up to 6 GHz, so I wanted to see if there are other satellites out there might might also be able to be used. The neat part is with a on-orbit emitter, there are less limitations on being co-located with a terrestrial transmitter (theoretically of course).

[jomosh]

O-I812, are you able to join the Discord channel? Link is on the main page for this github project.