I am really glad I decided to use Jupyter notebook to code this. I have learnt quite a bit about DSP and GNURadio blocks and having a notebook to test code, produce plots and write documentation at the same place is just wonderful.
So my latest commit shows the response of a sweep using the probe Avg Mag ^2 but it is very slow at 2 seconds for 10MHz so a full 50-2400MHz sweep would take about 10 minutes.
So time to figure out how to do FFT.
Using a stream to vector I get an 'array' of complex numbers that I can put into a vector sink. This is an ever increasing collection of data that can be looked at, but it doesn't show 'instantaneous' time slice snapshot. So next I put that through an FFT. And since the output of an FFT is also complex, I used a complex to mag block. Then I found the vector probe which is similar to the earlier mag probe I used, and that meant I could get the latest values from the stream to vector or FFT output.
The plot after the FFT was different from the earlier avg-mag plot, so it seems I still need to do some DSP learning.