The CCIR considering: a) that equipment built to operate on the CCIR Recommendation 601 digital video standard utilizes a sampling frequency of 13.5 MHz, of which the ninth harmonic coincides exactly with an international distress frequency of 121.5 MHz*; b) that 243 MHz*, or the eighteenth harmonic of the sampling frequency, is also reserved for international distress use; c) that these distress signais are usually detected by aircraft or satellite receivers, and sophisticated signal processing is required for reliable detection; d) that No.964 of the Radio Regulations prohibits any harmful interference on the emergency frequencies.
ITU-R BT.803 FRENCH-1992 history
1992ITU-R BT.803 FRENCH-1992 Avoidance of Interference Generated by Digital Television Studio Equipment