Playback of the Recorded IQ Data

Yesterday I described how to record the IQ data from the USRP focusing on generating unique file names every time the GNU Radio / GRC script is executed. Playing the recorded IQ data is really simple: We take the corresponding receiver application and replace the USRP source with a file source and a throttle block.

The recorded IQ data is a simple binary file containing nothing more than the received samples. There is no information about frequency or sample rate which is why we need a throttle block to maintain a constant sample rate in the receiver.

My experimental application was forĀ  reception of APT signals from the NOAA weather satellites so my playback application is a WFM receiver. You can get the example .grc file here. Sorry, but the .grc file is no longer available

GNU Radio Companion flow graph for playing back recorded IQ data

And here is a video showing the playback in action. The receiver can be used exactly the same way as when it receives the samples from the USRP. A really great and very useful feature in GNU Radio!

Author: Alexandru Csete

Embedded software engineer in the satcom industry during the day. Radio amateur and SDR hacker during the night.