Professor Jason from Harvery Mudd College in California has recently uploaded a 23 lesson video series on software defined radio digital signal processing (DSP) concepts that can be learned with an RTL-SDR, PlutoSDR and GNU Radio.

If you're looking for a University level introduction to DSP this looks like a good hand on approach to learning. It covers concepts from a simple FM radio receove in GNU Radio, to doppler radar with PlutoSDR, to digital modulation, pulse shaping, GPS reception and more.

All the GNU Radio flowgraphs are available on their class GitHub as well.