Some more tests with a probe.. this time from kretz technik. Raw acquisition yield interesting signals.. Doesn't it look like a night sky ?

The spectrum seems to contain good ultrasound (with a fair dose of noise) - the signal is between the blue lines, between 2.2MHz and 4.2MHz:

Which yield a classical wirephantom image.

See more on the notebook -- https://github.com/kelu124/echomods/blob/master/matty/20180901a/20180901a-Client.ipynb