Hi The problem is that waterfall sink does not have the option 'Control panel' in the 'Config' tab.One should be able to toggle the control panel on and off. The control panel can be seen e.g. in the figure at
https://wiki.gnuradio.org/index.php/QT_GUI_Waterfall_Sink This problem is similar to https://stackoverflow.com/questions/69413916/how-to-expose-the-control-panel-of-the-qt-gui-time-sink I have Ubuntu 20.04.4 LTS and GRC 3.8.1.0 (Python 3.8.10) cheers, Kimmo
