The width of a frequency band such that, below the lower and above the upper frequency limits, the mean powers emitted are each equal to a specified percentage B/2 of the total mean power of a given emission. Unless otherwise specified by the CCIR for the appropriate class of emission, the value of B/2 should be taken as 0. 5%. Note 1: The percentage of the total power outside the occupied bandwidth is represented by B. Note 2: In some cases, e. G. , multichannel frequency-division multiplexing systems, use of the 0. 5% limits may lead to certain difficulties in the practical application of the definition of occupied and necessary bandwidth; in such cases, a different percentage may prove useful. 2. The frequency bandwidth such that, below its lower and above its upper frequency limits, the mean powers radiated are each equal to 0. 5% of the total mean power radiated by a given emission.