I'm brand new to SDR and I'm just trying to calibrate my expectations of what will be possible in real time. I'm hoping someone here can give me a pointer or two.
I'm running GNU Radio 3.7.2 on Ubuntu 14.04, having installed from the Ubuntu repositories. The machine I'm using has an Intel Core i5-2520M running at 2500MHz.
I'm constructing flowgraphs in GRC and using an RTL-2832U-based USB dongle as a receiver.
I've built a fairly simple broadcast FM stereo receiver as an example. It has the following components:
* RTL-SDR source (768k sample rate).
* Low pass filter (768k sample rate, 96k cutoff, 4k transition)
* Rational resampler (4x decimation)
* WBFM receiver (quadrature rate 192k)
* Low pass filter (1x decimation, 192k sample rate, 15k cutoff, 2k transition)
* 2x Band pass filter (1x decimation, 192k sample rate, differing cutoff and transition)
* Multiply
* Low pass filter (192k sample rate, 15k cutoff, 2k transition)
* Add, subtract
* 2 x rational resampler (4x decimation)
* Audio sink (sample rate 48k)
My system is not able to run this in realtime, producing regular underruns (about two per second). Decreasing the receiver sample rate to 384k and decreasing the decimation factor in the first resampler to 2 allows it to run in without underruns, from which I deduce that the CPU is right on the edge of being able to process the flowchart in realtime.
Are my expectations of what I'll be able to do in realtime unreasonably high? Is there something I'm missing, that I can do to make this run much faster?
Thanks,
Tom