International Frequency Register Section 26.4. (MIFR) and dated. The essence of the MIFR is published twice a year in microfiche by the ITU, as the International Frequency 26.2.4 Elimination of interference List (IFL). A list of newly notified national assignments, together with an up-dating of the IFL, is circulated weekly to If all the necessary preliminary checks and consultations have been administrations by the IFRB. carried out effectively before a new assignment is brought into 26/6 Radio spectrum management operation, interference should not arise. However, radio propaga- covers the frequency range 9kHz to 275GHz, divided into hundreds tion predictions are imperfect, the use that will be made of fre- of frequency bands, allocated for 33 different services. quency assignments is not always clearly foreseen at the outset and Different countries need the various kinds of radio facilities in the need grows every year to squeeze more and more systems into different proportions. Consequently, a rigid and uniform global the most desirable frequency bands. Interference does arise. pattern of frequency allocation would not be acceptable. The need If the station suffering interference provides what is called a safety for flexibility has been met in three ways: service, typically a communication or radio navigation system upon which the safety of human life may depend, the interfering station 1. Many frequency bands have been allocated, not for one but for stops using the assignment immediately. several services; these bands are said to be shared. Usually all If the assignment suffering interference and the assignment caus- services sharing a band have equal rights of access to it, but ing interference have both been made by the same administration, there are bands in which one service is given primary status and then that administration resolves the problem, typically by assig- another has an inferior, secondary status. As mentioned in ning another frequency to one of the links. section 26.2.4, the status of the al