A complex concept regarding how well ATV schemes work with existing television receivers, transmission channels, home video equipment, and professional production equipment. See also Channel- Compatible, Receiver-Compatible. A. ATV Receiver Compatibility Levels Level 5 – ATV signal is displayed as ATV on an NTSC TV set Level 4 – ATV signal appears as highest quality NTSC on an NTSC TV set Level 3 – ATV signal appears as reduced quality NTSC on an NTSC TV set Level 2 – ATV signal requires inexpensive adapter for an NTSC TV set Level 1 – ATV signal requires expensive adaptor for an NTSC TV set Level 0 – ATV signal cannot be displayed on an NTSC TV set B. Compatible ATV Transmission Schemes • Receiver-compatible and channel-compatible single 6 MHz channel • Receiver-compatible channel plus augmentation channel • Necessarily adjacent augmentation channel • Not necessarily adjacent augmentation channel • Non-receiver-compatible channel plus simulcast channel.