The west coast ESSB group is a collection of operators and stations spread mostly across California, Oregon, and Nevada (with some Washington, Idaho, and other flavors from time to time). ESSB is Enhanced (or Extended) Single Side Band. Different people have different definitions of what “Enhanced” means, but for this group it is about optimal fidelity – which means extended frequency response compared to the typical 2.8 khz (give or take) bandwidth.

A variety of radios support ESSB – multiple Yaesu (including the current FTDX101 and FTDX10 – they call it TTBF mode), Kenwood, and SDRs including Apache Labs Anan, Flex, and Sun. Currently, Icom radios do not support ESSB transmit.

Below is the FCC response to a claim complaining about extended bandwidth – please read at your leisure. tl;dr – FCC rejected the petition to mandate narrow bandwidth.