Many handie-talky radios suffer from severe interference from nearby transmitters -- particularly on hilltop sites. Blocking is a reduction in sensitivity that can be hard to detect.
When a radio is being blocked all callers (even strong ones) can appear weak or may even be undetectable.
The SOTABEAMS bandpass filter is a small, rugged and lightweight filter that eleminates virtually all interference problems. The filter is a helical design that is made specially for SOTABEAMS. It is simply attached between the radio and antenna.
Richard of SOTABEAMS has made a short video about various methods to combat blocking which can be seen on the SOTABEAMS website: https://www.sotabeams.co.uk/bandpass-filter-for-2m/