Adjacent Signal Selectivity: Section 6.1 of ETSI EN 303 372-2 (RED testing). Bad procedure/standard?
The test measures the DUT's sensitivity while in the presence of an in-band, adjacent channel interferer. It measures a ratio, the source level (6.1 C) vs the interferer (6.1 D) Since it is a ratio, the absolute level does not matter for linear systems. The desired signal is set to the quasi free error level, that is usually 3 to 6dB above the sensitivity level.