Abstract: Items of auxiliary information are transmitted in an AM radio broadcast signal by phase angle modulating the AM carrier with digitally encoded data representing the auxiliary information. The items of auxiliary information are allocated to a cyclically recurring number of groups, each group consists of two equal length information blocks. Each information block includes an information word and a check word. Different offset words are superimposed on the respective ones of the check words. The offset words are useful for the synchronization of the information blocks in a receiver.