The research and application of gob-side entry retaining (GER) technology in Chinese coal mines has been over 60 years. Two major technical types including GER with filling and GER with roof cutting were developed. However. due to the complex mining and geological conditions of the mined-out coal seam in different mining areas. https://www.roneverhart.com/Behringer-UL-1000G2-Wireless-In-Ear-Monitoring-System-US-584-to-608-MHz-p31393/