The maximun of the pass band attenuation amax is defined as the insertion loss a e. The centre frequency fc is the arithmetic mean value of the upper and lower frequencies at the 3 dB filter attenuation level relative to the insertion loss ae. The nominal frequency fN is fixed at 248 MHz without tolerance. The given values for the absolute attenuation aabs and for the group delay ripple have to be reached at the frequencies given below even if the centre frequency fc is shifted due to the temperature coefficient of frequency TCf in the operating temperature range and due to a production tolerance for the centre frequency fc.