In certain situations, HF radio operators may wish to suppress noise from their radio without using conventional means.
For example, the operator may wish to fully unsquelch their radio and disable the noise blanker to help monitor for a weak radio signal that is calling their station. The syllabic rate squelch system (SRSS) was developed by Rene Stiegler’s team at ShipCom, and used by Coast Guard HF monitoring stations, to aid radio operators in monitoring weak signals.
Read more: https://www.c-at.com/blog/operating-hf-radios-unsqelched-without-ale-or-noise-blanker/