A small circuit board that is intended to protect the receiver against overvoltages, for example from nearby transmitting stations.
Warning
The circuit board is a circuit suggestion. The author does not guarantee functionality!
Note
I just ordered PCB. Once the board has been delivered I will measure it with a NanoVNA and post the results... Be patient
A diode with 0.3V forward voltage suppresses higher voltages. If a current >50mA occurs, the self-resetting PTC fuse trips.
Board has been designed with: https://easyeda.com