The maximum of the pass band attenuation amax within the usable signal band width is defined as the insertion loss ae. The insertion loss ae is the reference value for relative attenuation . The nominal frequency fN is fixed on 443.400 MHz. The centre frequency fo 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 given values for the relative attenuation arel and for the group delay ripple have to be reached at the frequencies given below also if the centre frequency fo 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 fo.